阅读说明：本技术 一种4-环己亚胺甲基取代苯并呋喃衍生物的合成方法 (Synthesis method of 4-cyclohexylimine methyl substituted benzofuran derivative ) 是由 赵应伟 汤须崇 于 2021-09-23 设计创作，主要内容包括：本发明提供了一种4-环己亚胺甲基取代苯并呋喃衍生物的合成方法,属于有机合成技术领域。本发明在Lewis酸催化剂的催化下,利用对苯醌与乙酰乙酸乙酯进行缩合反应,得到5-羟基-2-甲基苯并呋喃-3-羧酸乙酯,之后进行甲基化反应,得到5-甲氧基-2-甲基苯并呋喃-3-羧酸乙酯,再在碱性条件下进行水解反应,得到5-甲氧基-2-甲基苯并呋喃-3-羧酸,之后在缩合剂和碱的存在下,与R-苯胺进行缩合反应,得到5-甲氧基-2-甲基-N-R-苯基苯并呋喃-3-甲酰胺,经脱甲基反应后得到5-羟基-2-甲基-N-R-苯基苯并呋喃-3-甲酰胺,最后与甲醛、环己亚胺发生Mannich反应,得到终产物。(The invention provides a synthesis method of a 4-cyclohexylimine methyl substituted benzofuran derivative, belonging to the technical field of organic synthesis. The invention utilizes p-benzoquinone and ethyl acetoacetate to carry out condensation reaction under the catalysis of Lewis acid catalyst to obtain 5-hydroxy-2-methylbenzofuran-3-carboxylic acid ethyl ester, then carries out methylation reaction to obtain 5-methoxy-2-methylbenzofuran-3-carboxylic acid ethyl ester, carries out hydrolysis reaction under alkaline condition to obtain 5-methoxy-2-methylbenzofuran-3-carboxylic acid, then carries out condensation reaction with R-aniline under the existence of condensing agent and alkali to obtain 5-methoxy-2-methyl-N-R-phenylbenzofuran-3-formamide, obtains 5-hydroxy-2-methyl-N-R-phenylbenzofuran-3-formamide after demethylation reaction, finally, the intermediate is subjected to Mannich reaction with formaldehyde and cycloheximide to obtain a final product.)

1. A synthesis method of a 4-cycloheximide methyl substituted benzofuran derivative is disclosed, wherein the 4-cycloheximide methyl substituted benzofuran derivative has a structure shown in a formula 1:

r is m-CH₃、p-CH₃、m-CF₃Or p-CF₃。

The synthesis method of the 4-cyclohexylimine methyl substituted benzofuran derivative comprises the following steps:

(1) under the catalysis of a Lewis acid catalyst, performing condensation reaction on benzoquinone and ethyl acetoacetate to obtain 5-hydroxy-2-methylbenzofuran-3-carboxylic acid ethyl ester;

(2) carrying out methylation reaction on the 5-hydroxy-2-methylbenzofuran-3-carboxylic acid ethyl ester and a methylating agent to obtain 5-methoxy-2-methylbenzofuran-3-carboxylic acid ethyl ester;

(3) carrying out hydrolysis reaction on the 5-methoxy-2-methylbenzofuran-3-carboxylic acid ethyl ester in an alkaline solution, and acidifying to obtain 5-methoxy-2-methylbenzofuran-3-carboxylic acid;

(4) in the presence of a condensing agent and an alkaline compound, carrying out condensation reaction on the 5-methoxy-2-methylbenzofuran-3-carboxylic acid and R-aniline to obtain 5-methoxy-2-methyl-N-R-phenylbenzofuran-3-formamide;

(5) performing demethylation reaction on the 5-methoxy-2-methyl-N-R-phenylbenzofuran-3-formamide and a demethylation reagent to obtain 5-hydroxy-2-methyl-N-R-phenylbenzofuran-3-formamide;

(6) the 5-hydroxy-2-methyl-N-R-phenyl benzofuran-3-formamide has a Mannich reaction with formaldehyde and cycloheximide to obtain the 4-cycloheximide methyl substituted benzofuran derivative with the structure shown in the formula 1.

2. The synthesis method according to claim 1, wherein the molar ratio of p-benzoquinone to ethyl acetoacetate in the step (1) is 1 (1-3);

the condensation reaction is carried out at the temperature of 60-100 ℃ for 8-24 h.

3. The synthesis method according to claim 1 or 2, wherein the Lewis acid catalyst in the step (1) is one or more of aluminum trichloride, boron trifluoride, sulfur trioxide, ferric bromide and zinc chloride.

4. The synthesis method according to claim 1, wherein the methylating agent in the step (2) is one or more of dimethyl sulfate, dimethyl carbonate, methyl iodide, methyl bromide, methyl p-toluenesulfonate and a formaldehyde-formic acid system;

the molar ratio of the 5-hydroxy-2-methylbenzofuran-3-carboxylic acid ethyl ester to the methylating agent is 1 (1-5).

5. The synthesis method according to claim 1, wherein the pH value of the alkaline solution in the step (3) is 10-13.

6. The synthesis method of claim 1, wherein the condensing agent in step (4) is one or more of CDI, EDCI, HATU and HBTU;

the alkaline compound is one or more of N, N-diisopropylethylamine, potassium tert-butoxide, potassium acetate, potassium phosphate and triethylamine.

7. The synthesis method according to claim 1, wherein the molar ratio of the 5-methoxy-2-methylbenzofuran-3-carboxylic acid to the R-aniline in the step (4) is 1 (1-5);

the R group in the R-aniline is m-CH₃、p-CH₃、m-CF₃Or p-CF₃。

8. The synthesis method of claim 1, wherein the demethylating reagent in step (5) is one or more of boron bromide, hydrobromic acid and an aluminum trichloride-pyridine system.

9. The synthesis method according to claim 1 or 8, wherein the molar ratio of the 5-methoxy-2-methyl-N-R-phenylbenzofuran-3-carboxamide to the demethylating agent in the step (5) is 1 (0.5-2).

10. The synthesis method of claim 1, wherein in the step (6), the molar ratio of 5-hydroxy-2-methyl-N-R-phenylbenzofuran-3-carboxamide to formaldehyde to cyclohexylimine is 1 (1-3) to (1-3);

the temperature of the Mannich reaction is 70-110 ℃, and the time is 10-24 h.

Technical Field

The invention relates to the technical field of organic synthesis, in particular to a synthesis method of a 4-cyclohexylimine methyl substituted benzofuran derivative.

Background

The oncogenic transcription factor c-MYC has a pleiotropic role in cells, plays a key role in the development of cancer, and has limited small molecules capable of selectively inhibiting the function or expression of the oncogenic transcription factor c-MYC.

Benzofuran and its derivatives are common building blocks for the construction of drug molecules, widely present in natural products and bioactive molecules. The benzofuran structural molecule can effectively inhibit the expression of c-MYC, wherein DC-34 (4-cyclohexylimine methyl substituted benzofuran derivative, formula 1) is the most effective one (David R Calabrese, Nature Communications, 2018).

The known synthetic route of the 4-cyclohexylimine methyl substituted benzofuran derivative is as follows:

when the 4-cyclohexylimine methyl substituted benzofuran derivative with the structure shown as I is synthesized by adopting the route, R is p-trifluoromethyl, more side reactions occur, and the yield of a final product is low and is only about 50%.

Disclosure of Invention

In view of the above, the present invention aims to provide a method for synthesizing a 4-cyclohexylimine methyl substituted benzofuran derivative. The 4-cyclohexylimine methyl substituted benzofuran derivative obtained by the synthetic method has high yield.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a synthesis method of a 4-cycloheximide methyl substituted benzofuran derivative, wherein the 4-cycloheximide methyl substituted benzofuran derivative has a structure shown in a formula 1:

r is m-CH₃、p-CH₃、m-CF₃Or p-CF₃。

The synthesis method of the 4-cyclohexylimine methyl substituted benzofuran derivative comprises the following steps:

(1) under the catalysis of a Lewis acid catalyst, performing condensation reaction on benzoquinone and ethyl acetoacetate to obtain 5-hydroxy-2-methylbenzofuran-3-carboxylic acid ethyl ester;

(2) carrying out methylation reaction on the 5-hydroxy-2-methylbenzofuran-3-carboxylic acid ethyl ester and a methylating agent to obtain 5-methoxy-2-methylbenzofuran-3-carboxylic acid ethyl ester;

(3) carrying out hydrolysis reaction on the 5-methoxy-2-methylbenzofuran-3-carboxylic acid ethyl ester in an alkaline solution, and acidifying to obtain 5-methoxy-2-methylbenzofuran-3-carboxylic acid;

(4) in the presence of a condensing agent and an alkaline compound, carrying out condensation reaction on the 5-methoxy-2-methylbenzofuran-3-carboxylic acid and R-aniline to obtain 5-methoxy-2-methyl-N-R-phenylbenzofuran-3-formamide;

(5) performing demethylation reaction on the 5-methoxy-2-methyl-N-R-phenylbenzofuran-3-formamide and a demethylation reagent to obtain 5-hydroxy-2-methyl-N-R-phenylbenzofuran-3-formamide;

(6) the 5-hydroxy-2-methyl-N-R-phenyl benzofuran-3-formamide has a Mannich reaction with formaldehyde and cycloheximide to obtain the 4-cycloheximide methyl substituted benzofuran derivative with the structure shown in the formula 1.

Preferably, the molar ratio of p-benzoquinone to ethyl acetoacetate in the step (1) is 1 (1-3);

the condensation reaction is carried out at the temperature of 60-100 ℃ for 8-24 h.

Preferably, the Lewis acid catalyst in step (1) is one or more of aluminum trichloride, boron trifluoride, sulfur trioxide, ferric bromide and zinc chloride.

Preferably, the methylating agent in the step (2) is one or more of dimethyl sulfate, dimethyl carbonate, methyl iodide, methyl bromide, methyl p-toluenesulfonate and a formaldehyde-formic acid system;

the molar ratio of the 5-hydroxy-2-methylbenzofuran-3-carboxylic acid ethyl ester to the methylating agent is 1 (1-5).

Preferably, the pH value of the alkaline solution in the step (3) is 10-13.

Preferably, the condensing agent in the step (4) is one or more of CDI, EDCI, HATU and HBTU;

the alkaline compound is one or more of N, N-diisopropylethylamine, potassium tert-butoxide, potassium acetate, potassium phosphate and triethylamine.

Preferably, the molar ratio of the 5-methoxy-2-methylbenzofuran-3-carboxylic acid to the R-aniline in the step (4) is 1 (1-5);

the R group in the R-aniline is m-CH₃、p-CH₃、m-CF₃Or p-CF₃。

Preferably, the demethylating reagent in the step (5) is one or more of boron bromide, hydrobromic acid and an aluminum trichloride-pyridine system.

Preferably, the molar ratio of the 5-methoxy-2-methyl-N-R-phenylbenzofuran-3-formamide to the demethylating reagent in the step (5) is 1 (0.5-2).

Preferably, the molar ratio of the 5-hydroxy-2-methyl-N-R-phenyl benzofuran-3-formamide to the formaldehyde to the cyclohexylimine in the step (6) is 1 (1-3) to (1-3);

the temperature of the Mannich reaction is 70-110 ℃, and the time is 10-24 h.

The invention provides a synthesis method of 4-cyclohexylimine methyl substituted benzofuran derivatives, which comprises the steps of firstly carrying out condensation reaction on p-benzoquinone and ethyl acetoacetate under the catalysis of a Lewis acid catalyst to obtain 5-hydroxy-2-methylbenzofuran-3-carboxylic acid ethyl ester, then carrying out methylation reaction on the ethyl ester and a methylating agent to obtain 5-methoxy-2-methylbenzofuran-3-carboxylic acid ethyl ester, then carrying out hydrolysis reaction under an alkaline condition to obtain 5-methoxy-2-methylbenzofuran-3-carboxylic acid, and then carrying out condensation reaction on the 5-methoxy-2-methylbenzofuran-3-carboxylic acid and R-aniline in the presence of a condensing agent and alkali to obtain 5-methoxy-2-methyl-N-R-phenyl benzofuran- 3-formamide, obtaining 5-hydroxy-2-methyl-N-R-phenyl benzofuran-3-formamide after demethylation reaction, and finally carrying out Mannich reaction on the 5-hydroxy-2-methyl-N-R-phenyl benzofuran-3-formamide, formaldehyde and cycloheximide to obtain the 4-cycloheximide methyl substituted benzofuran derivative. The method for synthesizing the 4-cyclohexylimine methyl substituted benzofuran derivative by adopting the route has the advantage of less side reaction, and the obtained 4-cyclohexylimine methyl substituted benzofuran derivative has high yield; the invention takes formaldehyde and cycloheximide as raw materials to synthesize 4-cycloheximide methyl, wherein imine positive ions generated in situ by formaldehyde and amine can generate Mannich reaction with 5-hydroxy-2-methyl-N-R-phenyl benzofuran-3-formamide to further generate the 4-cycloheximide methyl substituted benzofuran derivative, thereby further avoiding side reaction. Meanwhile, the p-benzoquinone and the ethyl acetoacetate are used as reaction raw materials, so that the raw materials are wide in source and low in cost, and the method is suitable for industrial batch production.

Drawings

FIG. 1 is a synthetic route of 4-cyclohexylimine methyl substituted benzofuran derivatives;

FIG. 2 shows the preparation of ethyl 5-hydroxy-2-methylbenzofuran-3-carboxylate obtained in example 1¹H-NMR chart;

FIG. 3 is a drawing showing the preparation of ethyl 5-methoxy-2-methylbenzofuran-3-carboxylate obtained in example 1¹H-NMR chart;

FIG. 4 shows the preparation of 5-methoxy-2-methyl-N-p-trifluoromethylphenylbenzofuran-3-carboxamide (7) obtained in example 1¹H-NMR chart;

FIG. 5 shows the preparation of 5-hydroxy-2-methyl-N-p-trifluoromethylphenylbenzofuran-3-carboxamide obtained in example 1¹H-NMR chart;

FIG. 6 shows the preparation of 4-cyclohexyliminomethyl-substituted benzofurans from example 1¹H-NMR chart.

Detailed Description

The invention provides a synthesis method of a 4-cycloheximide methyl substituted benzofuran derivative, wherein the 4-cycloheximide methyl substituted benzofuran derivative has a structure shown in a formula 1:

r is m-CH₃、p-CH₃、m-CF₃Or p-CF₃. In the present invention, the m-CH₃Represents meta-CH₃，p-CH₃Represents para CH₃(ii) a The m-CF₃Represents meta-CF₃，p-CF₃Represents para-CF₃。

The 4-cyclohexylimine methyl substituted benzofuran derivative has a specific structure shown in a table 1:

the synthesis method of the 4-cyclohexylimine methyl substituted benzofuran derivative comprises the following steps:

(1) under the catalysis of a Lewis acid catalyst, performing condensation reaction on benzoquinone and ethyl acetoacetate to obtain 5-hydroxy-2-methylbenzofuran-3-carboxylic acid ethyl ester;

(2) carrying out methylation reaction on the 5-hydroxy-2-methylbenzofuran-3-carboxylic acid ethyl ester and a methylating agent to obtain 5-methoxy-2-methylbenzofuran-3-carboxylic acid ethyl ester;

(3) carrying out hydrolysis reaction on the 5-methoxy-2-methylbenzofuran-3-carboxylic acid ethyl ester in an alkaline solution, and acidifying to obtain 5-methoxy-2-methylbenzofuran-3-carboxylic acid;

(4) in the presence of a condensing agent and an alkaline compound, carrying out condensation reaction on the 5-methoxy-2-methylbenzofuran-3-carboxylic acid and R-aniline to obtain 5-methoxy-2-methyl-N-R-phenylbenzofuran-3-formamide;

(5) performing demethylation reaction on the 5-methoxy-2-methyl-N-R-phenylbenzofuran-3-formamide and a demethylation reagent to obtain 5-hydroxy-2-methyl-N-R-phenylbenzofuran-3-formamide;

(6) the 5-hydroxy-2-methyl-N-R-phenyl benzofuran-3-formamide has a Mannich reaction with formaldehyde and cycloheximide to obtain the 4-cycloheximide methyl substituted benzofuran derivative with the structure shown in the formula 1.

In the invention, under the catalysis of a Lewis acid catalyst, benzoquinone and ethyl acetoacetate are subjected to condensation reaction to obtain 5-hydroxy-2-methylbenzofuran-3-carboxylic acid ethyl ester. In the invention, the Lewis acid catalyst is preferably one or more of aluminum trichloride, boron trifluoride, sulfur trioxide, ferric bromide and zinc chloride. In the present invention, the molar ratio of p-benzoquinone to ethyl acetoacetate is preferably 1 (1-3), more preferably 1 (1-2).

In the invention, the organic solvent used in the condensation reaction is preferably one or more of dichloromethane, chloroform, methanol, ethanol, acetonitrile and tetrahydrofuran.

In the invention, the condensation reaction temperature is preferably 60-100 ℃, and more preferably 70-80 ℃; the time is preferably 10 to 24 hours, and more preferably 15 to 20 hours.

After the condensation reaction, the invention preferably carries out post-treatment on the obtained condensation reaction liquid; in the present invention, the post-treatment preferably comprises the steps of:

removing the organic solvent in the condensation reaction liquid, and sequentially carrying out organic phase extraction, concentration and column chromatography separation on the obtained residue to obtain the pure 5-hydroxy-2-methylbenzofuran-3-carboxylic acid ethyl ester.

In the present invention, the organic solvent in the condensation reaction liquid is preferably removed by rotary evaporation. The residue obtained after removal of the organic solvent was a black viscous mass. In the present invention, the organic solvent used in the organic phase extraction is preferably ethyl acetate. The present invention does not require any particular means for concentration, and may employ any means for concentration known to those skilled in the art. The column chromatography separation is preferably carried out by using a silica gel column, the mobile phase of the column chromatography separation is preferably petroleum ether and ethyl acetate, and the volume ratio of the petroleum ether to the ethyl acetate is preferably 10: 1.

In the invention, the structural formula of the 5-hydroxy-2-methylbenzofuran-3-carboxylic acid ethyl ester is shown as a formula 2.

After the 5-hydroxy-2-methylbenzofuran-3-carboxylic acid ethyl ester is obtained, methylation reaction is carried out on the 5-hydroxy-2-methylbenzofuran-3-carboxylic acid ethyl ester and a methylating agent to obtain the 5-methoxy-2-methylbenzofuran-3-carboxylic acid ethyl ester. In the invention, the methylating agent is preferably one or more of dimethyl sulfate, dimethyl carbonate, methyl iodide, methyl bromide, methyl p-toluenesulfonate and a formaldehyde-formic acid system. In the invention, the molar ratio of the ethyl 5-hydroxy-2-methylbenzofuran-3-carboxylate to the methylating agent is preferably 1 (1-5), and more preferably 1 (2-3).

In the present invention, the organic solvent used in the methylation reaction is preferably acetonitrile; the catalyst used in the methylation reaction is preferably potassium carbonate. In the present invention, the mass ratio of the ethyl 5-hydroxy-2-methylbenzofuran-3-carboxylate to potassium carbonate is preferably 1: 2.

In the invention, the temperature of the methylation reaction is preferably 60-100 ℃, and more preferably 80 ℃; the time is 12-24 h.

In the present invention, after the methylation reaction, the present invention preferably performs a post-treatment on the obtained methylation reaction liquid; in the present invention, the post-treatment preferably comprises the steps of:

and sequentially filtering and separating by column chromatography to obtain the pure 5-methoxy-2-methylbenzofuran-3-carboxylic acid ethyl ester. The column chromatography separation is preferably carried out by using a silica gel column, and the mobile phase of the column chromatography separation is preferably ethyl acetate.

In the invention, the structural formula of the 5-methoxy-2-methylbenzofuran-3-carboxylic acid ethyl ester is shown as a formula 3:

after the 5-methoxy-2-methylbenzofuran-3-carboxylic acid ethyl ester is obtained, carrying out hydrolysis reaction on the 5-methoxy-2-methylbenzofuran-3-carboxylic acid ethyl ester in an alkaline solution, and acidifying to obtain the 5-methoxy-2-methylbenzofuran-3-carboxylic acid. In the invention, the alkaline solution is preferably one or more of aqueous solution of sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate; the pH value of the alkaline condition is preferably 10-13, and more preferably 11-12. In the present invention, it is preferable that the hydrolysis reaction is carried out by dissolving ethyl 5-methoxy-2-methylbenzofuran-3-carboxylate in an organic solvent and adding the solution to an alkaline solution in the form of an organic solution of ethyl 5-methoxy-2-methylbenzofuran-3-carboxylate. In the present invention, the organic solvent is preferably ethanol.

In the invention, the temperature of the hydrolysis reaction is preferably 60-80 ℃, and more preferably 70 ℃; the time is preferably 12 to 24 hours, and more preferably 16 to 20 hours.

In the present invention, after the hydrolysis reaction, the hydrolysis reaction liquid obtained in the present invention is preferably subjected to a post-treatment, and the post-treatment preferably includes the steps of:

removing the organic solvent in the hydrolysis reaction liquid, adjusting the pH value of the obtained residual liquid to 3, and separating out solids;

and sequentially washing the obtained solid, redissolving the solid by using an organic solvent, drying and removing the organic solvent to obtain a pure 5-methoxy-2-methylbenzofuran-3-carboxylic acid product.

In the present invention, the washing is preferably water washing; the organic solvent used for the organic solvent redissolution is preferably ethyl acetate. In the present invention, the drying agent used for drying is preferably anhydrous sodium sulfate; the manner of removing the organic solvent is preferably rotary evaporation.

In the present invention, the structural formula of the 5-methoxy-2-methylbenzofuran-3-carboxylic acid is shown in formula 4:

after the 5-methoxy-2-methylbenzofuran-3-carboxylic acid is obtained, in the presence of a condensing agent and alkali, the 5-methoxy-2-methylbenzofuran-3-carboxylic acid and R-aniline are subjected to condensation reaction to obtain 5-methoxy-2-methyl-N-R-phenylbenzofuran-3-formamide. In the invention, the condensing agent is preferably one or more of CDI, EDCI, HATU and HBTU; the base is preferably one or more of N, N-Diisopropylethylamine (DIEPA), potassium tert-butoxide, potassium acetate, potassium phosphate and triethylamine.

In the present invention, the molar ratio of the 5-methoxy-2-methylbenzofuran-3-carboxylic acid to the R-aniline is preferably 1 (1 to 5), more preferably 1 (2 to 3). In the present invention, the mass ratio of the 5-methoxy-2-methylbenzofuran-3-carboxylic acid to the condensing agent is preferably 1 (4-8), and more preferably 1: 7.

In the present invention, the organic solvent used for the condensation reaction is preferably DMF.

In the invention, the condensation reaction temperature is preferably 70-100 ℃, and more preferably 80-90 ℃; the time is preferably 12 to 48 hours, and more preferably 24 to 36 hours.

After the condensation reaction, the invention preferably carries out post-treatment on the obtained condensation reaction liquid; in the present invention, the post-treatment preferably comprises the steps of:

sequentially carrying out organic solvent dilution, washing, back extraction, drying, concentration and column chromatography on the obtained condensation reaction liquid to obtain a crude product of the 5-methoxy-2-methyl-N-R-phenylbenzofuran-3-formamide;

recrystallizing the crude product of the 5-methoxy-2-methyl-N-R-phenylbenzofuran-3-formamide to obtain a pure product of the 5-methoxy-2-methyl-N-R-phenylbenzofuran-3-formamide.

In the present invention, the structural formula of the 5-methoxy-2-methyl-N-R-phenylbenzofuran-3-carboxamide is shown in formula 5:

after the 5-methoxy-2-methyl-N-R-phenylbenzofuran-3-formamide is obtained, the 5-methoxy-2-methyl-N-R-phenylbenzofuran-3-formamide and a demethylating reagent are subjected to demethylation reaction to obtain the 5-hydroxy-2-methyl-N-R-phenylbenzofuran-3-formamide. In the invention, the demethylating reagent is preferably one or more of boron bromide, hydrobromic acid and an aluminum trichloride-pyridine system. In the present invention, the molar ratio of the 5-methoxy-2-methyl-N-R-phenylbenzofuran-3-carboxamide to the demethylating agent is preferably 1 (0.5 to 2), and more preferably 1 (1 to 1.5).

In the present invention, the organic solvent used for the demethylation reaction is preferably dichloromethane.

In the present invention, the demethylation reaction is preferably carried out under nitrogen conditions; the temperature of the demethylation reaction is preferably-20-room temperature, and the time is preferably 8-12 h. In the present invention, the demethylation reaction is preferably carried out under stirring.

After the demethylation reaction, the present invention preferably performs post-treatment on the demethylation reaction liquid; in the present invention, the post-treatment preferably comprises the steps of:

quenching reaction, removing the organic solvent in the demethylation reaction liquid, adding water into the residual liquid, standing and layering to obtain an organic phase;

and drying, concentrating and recrystallizing the organic phase in sequence to obtain a pure product of the 5-hydroxy-2-methyl-N-p-trifluoromethyl phenyl benzofuran-3-formamide.

In the present invention, the quenching method is preferably: adding ice blocks into the demethoxylation reaction liquid, and adding hydrochloric acid under stirring.

In the present invention, the organic solvent is preferably removed by rotary evaporation; the present invention does not require any particular manner of drying and concentrating, and may be carried out by drying and concentrating means well known to those skilled in the art. In the present invention, the reagent for recrystallization is preferably ethyl acetate and/or petroleum ether.

In the invention, the structural formula of the 5-hydroxy-2-methyl-N- (R) -phenyl benzofuran-3-formamide is shown as a formula 6.

After the 5-hydroxy-2-methyl-N-R-phenylbenzofuran-3-formamide is obtained, the 5-hydroxy-2-methyl-N-R-phenylbenzofuran-3-formamide, formaldehyde and cycloheximide are subjected to Mannich reaction to obtain the 4-cycloheximide methyl substituted benzofuran derivative with the structure shown in the formula 1. In the invention, the molar ratio of the 5-hydroxy-2-methyl-N-R-phenylbenzofuran-3-formamide to the formaldehyde to the cyclohexylimine is preferably 1 (1-3) to (1-3), and more preferably 1 (1-2) to (1-2).

In the present invention, the organic solvent used in the Mannich reaction is preferably ethanol.

In the invention, the temperature of the Mannich reaction is 70-110 ℃, and more preferably 80-100 ℃; the time is 10-20 h, and more preferably 12 h.

After the Mannich reaction, the method preferably carries out post-treatment on the obtained Mannich reaction liquid; in the present invention, the post-treatment preferably comprises the steps of:

sequentially concentrating and separating by column chromatography to obtain a 4-cyclohexylimine methyl substituted benzofuran derivative crude product;

and sequentially carrying out organic solvent redissolution on the crude 4-cyclohexylimine methyl substituted benzofuran derivative, adding hydrochloric acid into the obtained liquid, and concentrating the organic solvent to obtain a pure 4-cyclohexylimine methyl substituted benzofuran derivative.

The present invention does not require any particular means for concentration, and may employ any means for concentration known to those skilled in the art. The column chromatography separation is preferably carried out by using a silica gel column, and the mobile phase of the column chromatography separation is preferably ethyl acetate.

In the present invention, the organic solvent used for the organic solvent redissolution is preferably ethyl acetate.

In the invention, the synthetic route of the 4-cyclohexylimine methyl substituted benzofuran derivative is shown in a figure 1.

The synthesis method of the 4-cyclohexylimine methyl substituted benzofuran derivative provided by the invention is described in detail below with reference to the examples, but the synthesis method is not to be construed as limiting the scope of the invention.

Example 1

The reaction is carried out according to formula I:

1) p-benzoquinone (1) (1.46g), ethyl acetoacetate (2) (1.8g), and anhydrous zinc chloride (2.6g) were dissolved in 250mL of a solvent, followed by a reaction at 80 ℃ under reflux for 12 hours. After the reaction, the solvent was removed by rotary evaporation to obtain a black viscous material. After addition of ethyl acetate, the organic phase was separated and the insoluble material was filtered off. The organic phase was concentrated and chromatographed on silica gel column (petroleum ether/ethyl acetate 10:1) to give 5-hydroxy-2-methylbenzofuran-3-carboxylic acid ethyl ester (3) as a white powdery solid in 86% yield.

The resulting ethyl 5-hydroxy-2-methylbenzofuran-3-carboxylate (3)¹The H-NMR chart is shown in FIG. 2;¹H NMR(500MHz,CDCl₃)δ7.50(s,1H),7.35–7.29(m,1H),6.83(dd,J＝8.7,2.5Hz,1H),5.86(s,1H),4.42(q,J＝7.1Hz,2H),2.76(s,3H),1.46(t,J＝7.1Hz,3H).

2) ethyl 5-hydroxy-2-methylbenzofuran-3-carboxylate (3) (14.8g) was weighed out, dissolved in 200mL of anhydrous acetonitrile, and 28g of anhydrous potassium carbonate and 40mL of methyl iodide were added. The reaction was refluxed at 80 ℃ for 12 h. And (3) tracking the reaction progress by TLC to find that partial raw materials are still not reacted completely, supplementing 12g of anhydrous potassium carbonate and 15mL of methyl iodide, and continuing refluxing for 12h, wherein the TLC shows that the reaction is complete. The KI formed and the unreacted potassium carbonate solid were filtered, and the filtrate was concentrated and subjected to chromatography on a silica gel column to give a pale yellow liquid as ethyl 5-methoxy-2-methylbenzofuran-3-carboxylate (4) in 83% yield.

The resulting ethyl 5-methoxy-2-methylbenzofuran-3-carboxylate (4)¹The H-NMR chart is shown in FIG. 3;¹H NMR(500MHz,CDCl₃)δ7.48(d,J＝2.6Hz,1H),7.33(d,J＝8.9Hz,1H),6.89(dd,J＝8.9,2.6Hz,1H),4.43(dd,J＝14.1,7.0Hz,2H),3.89(s,3H),2.77(s,3H),1.47(t,J＝7.1Hz,3H).

3) the obtained ethyl 5-methoxy-2-methylbenzofuran-3-carboxylate (4) (12.8g) was dissolved in 100mL of ethanol, and 100mL of an aqueous solution of 4.0g of potassium hydroxide was added to conduct a reflux reaction at 80 ℃ for 12 hours. After the TLC tracking reaction is finished, the ethanol is removed by rotary evaporation. 0.8mL of hydrochloric acid solution was added and the pH of the resulting solution was adjusted to 3, whereupon a large amount of yellow solid precipitated. The solid was filtered off with suction and washed three times with 100mL of water. The solid was dissolved in 200mL of ethyl acetate, separated to remove the residual aqueous layer, and dried by adding anhydrous sodium sulfate. Suction filtration and rotary evaporation to remove the solvent to finally obtain a light yellow solid which is 5-methoxy-2-methylbenzofuran-3-carboxylic acid (5) with a yield of 95%. The obtained product is not characterized and is directly put into the next reaction.

4) 0.4g of 5-methoxy-2-methylbenzofuran-3-carboxylic acid (5), 1.37g of p-trifluoromethylaniline (6a), 2.8g of 2- (7-azabenzotriazole) -N, N, N ', N' -tetramethyluronium Hexafluorophosphate (HATU), and 0.8mL of diisopropylethylamine were dissolved in 20mL of anhydrous DMF and reacted at 80 ℃ for 22 hours to obtain a brown solution. After cooling, 100mL of ethyl acetate was added for dilution and washed successively with 50mL of saturated ammonium chloride solution and 50mL of saturated sodium chloride solution. The organic layer was back-extracted with 100mL of saturated sodium chloride solution to remove DMF, which could not be precipitated by recrystallization. After drying and concentration of the solvent, chromatography is carried out with petroleum ether/ethyl acetate (10:1 to 1:1) column, and the crude product obtained contains a portion of 4-trifluoromethylaniline due to the proximity of polarity. Recrystallizing with petroleum ether/ethyl acetate as solvent, standing in a refrigerator at-20 deg.C overnight to obtain white crystal, and recrystallizing the mother liquor to obtain pure product. The total yield of the desired product 5-methoxy-2-methyl-N-p-trifluoromethylphenylbenzofuran-3-carboxamide (7a) is 75%.

Process for the preparation of the 5-methoxy-2-methyl-N-p-trifluoromethylphenylbenzofuran-3-carboxamide (7)¹The H-NMR chart is shown in FIG. 4;¹H NMR(500MHz,CDCl₃)δ7.78(d,J＝8.4Hz,2H),7.74(s,1H),7.66(d,J＝8.5Hz,2H),7.41(d,J＝8.9Hz,1H),7.18(d,J＝2.3Hz,1H),6.94(dd,J＝8.9,2.4Hz,1H),3.89(s,3H),2.76(s,3H).

5) 1.8g of 5-methoxy-2-methyl-N-p-trifluoromethylphenylbenzofuran-3-carboxamide (7a) are dissolved in 20mL of anhydrous dichloromethane. The reaction flask was placed in a-20 ℃ ice salt bath under nitrogen, 2.6mL of boron tribromide was carefully and rapidly added in one portion, and quickly added to an oil bubbler, maintaining an inert atmosphere. Stirring was maintained overnight, during which time the ice salt bath was allowed to slowly return to room temperature. After the reaction was complete, the ice was added back to the water bath and 0.8mL of hydrochloric acid was added dropwise slowly with vigorous stirring. After no bubble was generated, methylene chloride in the reaction mixture was removed by rotary evaporation, ethyl acetate was added (to absorb the boron compound coordinated to the product), water was added, and the layers were separated. The organic phase was washed with saturated sodium bicarbonate solution. After drying and concentration, it was recrystallized directly from ethyl acetate/petroleum ether without column chromatography. This gave 5-hydroxy-2-methyl-N-p-trifluoromethylphenylbenzofuran-3-carboxamide (8a) as an off-white solid (85% yield).

Process for preparing 5-hydroxy-2-methyl-N-p-trifluoromethylphenylbenzofuran-3-carboxamide (8)¹The H-NMR chart is shown in FIG. 5;¹H-NMR(500MHz,CDCl₃)δ7.92(d,J＝8.5Hz,2H),7.69(d,J＝8.5Hz,2H),7.31(d,J＝8.8Hz,1H),7.14(d,J＝2.2Hz,1H),6.81(dd,J＝8.8,2.3Hz,1H),2.66(s,3H).

6) 2.8g of 5-hydroxy-2-methyl-N-p-trifluoromethylphenylbenzofuran-3-carboxamide (8a), 0.8mL of 37% aqueous formaldehyde solution and 1.1mL of cyclohexylimine were dissolved in 50mL of absolute ethanol and reacted at 80 ℃ under reflux for 12 hours. TLC detection of the reaction process, after the reaction is finished, concentrating the solvent, and performing chromatography on a silica gel column. The crude product of the target amine is obtained and is sticky. Dissolving the precipitate in ethyl acetate, dropwise adding 0.3mL concentrated hydrochloric acid, concentrating the solvent under heating to separate out a large amount of white precipitate, filtering to obtain solid, washing with excessive ethyl acetate, and removing water in a vacuum drying oven for 4 h. The final 4-cyclohexyliminomethyl substituted benzofuran (9a) was obtained as the hydrochloride in 75% yield as a white solid.

Process for preparing 4-cyclohexyliminomethyl substituted benzofuran derivatives¹The H-NMR chart is shown in FIG. 6.¹H-NMR(500MHz,DMSO)δ11.30(s,1H),10.53(s,1H),9.30(s,1H),8.04(d,J＝8.3Hz,2H),7.78(d,J＝8.6Hz,2H),7.57(d,J＝8.9Hz,1H),7.13(d,J＝8.9Hz,1H),4.48(d,J＝5.2Hz,2H),3.30(dd,J＝8.4,5.3Hz,2H),3.20–3.10(m,2H),2.63(s,3H),1.76(d,J＝4.2Hz,4H),1.61–1.45(m,4H).

Example 2

Carrying out a reaction according to formula I;

1) p-benzoquinone (1) (1.51g), ethyl acetoacetate (2) (2.1g) and anhydrous zinc chloride (2.68g) were dissolved in 250mL of a solvent in the stated order of addition and then reacted at 80 ℃ under reflux for 12 hours. After the reaction, the solvent was removed by rotary evaporation to obtain a black viscous material. After addition of ethyl acetate, the organic phase was separated and the insoluble material was filtered off. The organic phase was concentrated and chromatographed on silica gel column (petroleum ether/ethyl acetate 10:1) to give 5-hydroxy-2-methylbenzofuran-3-carboxylic acid ethyl ester (3) as a white powdery solid in 85% yield.

2) Ethyl 5-hydroxy-2-methylbenzofuran-3-carboxylate (3) (15.2g) was weighed out, dissolved in 200mL of anhydrous acetonitrile, and 30g of anhydrous potassium carbonate and 42mL of methyl iodide were added. The reaction was refluxed at 80 ℃ for 12 h. The TLC tracks the reaction progress and finds that partial raw materials still remain unreacted, 14g of anhydrous potassium carbonate and 17mL of methyl iodide are added to the mixture to continue the reflux reaction for 12 hours, and the TLC shows that the reaction is complete. The KI formed and the unreacted potassium carbonate solid were filtered, and the filtrate was concentrated and subjected to chromatography on a silica gel column to give a pale yellow liquid as ethyl 5-methoxy-2-methylbenzofuran-3-carboxylate (4) in 83% yield.

3) The obtained ethyl 5-methoxy-2-methylbenzofuran-3-carboxylate (4) (13.0g) was dissolved in 100mL of ethanol, and 100mL of an aqueous solution of 4.2g of potassium hydroxide was added to conduct a reflux reaction at 80 ℃ for 12 hours. After the TLC tracking reaction is finished, the ethanol is removed by rotary evaporation. 0.9mL of hydrochloric acid solution was added and the pH of the resulting solution was adjusted to 3, whereupon a large amount of yellow solid precipitated. The solid was filtered off with suction and washed three times with 100mL of water. The solid was dissolved in 200mL of ethyl acetate, separated to remove the residual aqueous layer, and dried by adding anhydrous sodium sulfate. Suction filtration and rotary evaporation are carried out to remove the solvent, and light yellow solid which is 5-methoxy-2-methylbenzofuran-3-carboxylic acid (5) is finally obtained with the yield of 97%. The obtained product is not characterized and is directly put into the next reaction.

4) 0.6g of 5-methoxy-2-methylbenzofuran-3-carboxylic acid (5), 1.42g of p-trifluoromethylaniline (6a), 3.0g of 2- (7-azabenzotriazole) -N, N, N ', N' -tetramethyluronium Hexafluorophosphate (HATU), and 1.0mL of diisopropylethylamine were dissolved in 20mL of anhydrous DMF and reacted at 80 ℃ for 22 hours to obtain a brown solution. After cooling, 100mL of ethyl acetate was added for dilution and washed successively with 50mL of saturated ammonium chloride solution and 50mL of saturated sodium chloride solution. The organic layer was back-extracted with 100mL of saturated sodium chloride solution to remove DMF, which could not be precipitated by recrystallization. After drying and concentration of the solvent, chromatography is carried out with petroleum ether/ethyl acetate (10:1 to 1:1) column, and the crude product obtained contains a portion of 4-trifluoromethylaniline due to the proximity of polarity. Recrystallizing with petroleum ether/ethyl acetate as solvent, standing in a refrigerator at-20 deg.C overnight to obtain white crystal, and recrystallizing the mother liquor to obtain pure product. The total yield of the desired product, 5-methoxy-2-methyl-N-p-trifluoromethylphenylbenzofuran-3-carboxamide (7a), was 87%.

5) 2.0g of 5-methoxy-2-methyl-N-p-trifluoromethylphenylbenzofuran-3-carboxamide (7a) are dissolved in 20mL of anhydrous dichloromethane. The reaction flask was placed in a-20 ℃ ice salt bath under nitrogen, 2.8mL of boron tribromide was carefully and rapidly added in one portion, and quickly added to an oil bubbler, maintaining an inert atmosphere. Stirring was maintained overnight, during which time the ice salt bath was allowed to slowly return to room temperature. After the reaction was complete, the ice was added back to the water bath and 0.9mL of hydrochloric acid was added dropwise slowly with vigorous stirring. After no bubble was generated, methylene chloride in the reaction mixture was removed by rotary evaporation, ethyl acetate was added (to absorb the boron compound coordinated to the product), water was added, and the layers were separated. The organic phase was washed with saturated sodium bicarbonate solution. After drying and concentration, it was recrystallized directly from ethyl acetate/petroleum ether without column chromatography. This gave 5-hydroxy-2-methyl-N-p-trifluoromethylphenylbenzofuran-3-carboxamide (8a) as an off-white solid (86% yield).

6) 3.0g of 5-hydroxy-2-methyl-N-p-trifluoromethylphenylbenzofuran-3-carboxamide (8a), 1.0mL of 37% aqueous formaldehyde solution, and 1.3mL of cyclohexylimine were dissolved in 50mL of absolute ethanol and reacted at 80 ℃ under reflux for 12 hours. TLC detection of the reaction process, after the reaction is finished, concentrating the solvent, and performing chromatography on a silica gel column. The crude product of the target amine is obtained and is sticky. Dissolving the precipitate in ethyl acetate, dropwise adding 0.4mL concentrated hydrochloric acid, concentrating the solvent under heating to obtain a large amount of white precipitate, filtering to obtain solid, washing with excessive ethyl acetate, and removing water in a vacuum drying oven for 4 h. 4-Cyclohexaneiminomethyl-substituted benzofuran (9a) was obtained as the hydrochloride salt in 77% yield.

Example 3

The reaction is carried out according to formula I:

1) p-benzoquinone (1) (1.55g), ethyl acetoacetate (2) (2.3g) and anhydrous zinc chloride (2.70g) were dissolved in 250mL of a solvent in the stated order of addition and then reacted at 80 ℃ under reflux for 12 hours. After the reaction, the solvent was removed by rotary evaporation to obtain a black viscous material. After addition of ethyl acetate, the organic phase was separated and the insoluble material was filtered off. The organic phase was concentrated and chromatographed on silica gel column (petroleum ether/ethyl acetate 10:1) to give 5-hydroxy-2-methylbenzofuran-3-carboxylic acid ethyl ester (3) as a white powdery solid.

2) Ethyl 5-hydroxy-2-methylbenzofuran-3-carboxylate (3) (15.4g) was weighed out, dissolved in 200mL of anhydrous acetonitrile, and 32g of anhydrous potassium carbonate and 44mL of methyl iodide were added. The reaction was refluxed at 80 ℃ for 12 h. The TLC tracks the reaction progress and finds that partial raw materials still remain unreacted, 16g of anhydrous potassium carbonate and 19mL of methyl iodide are added to the mixture to continue the reflux reaction for 12 hours, and the TLC shows that the reaction is complete. The KI formed and the unreacted potassium carbonate solid were filtered, and the filtrate was concentrated and subjected to chromatography on a silica gel column to give a pale yellow liquid as ethyl 5-methoxy-2-methylbenzofuran-3-carboxylate (4) in 87% yield.

3) The obtained ethyl 5-methoxy-2-methylbenzofuran-3-carboxylate (4) (13.2g) was dissolved in 100mL of ethanol, and 100mL of an aqueous solution of 4.4g of potassium hydroxide was added to conduct a reflux reaction at 80 ℃ for 12 hours. After the TLC tracking reaction is finished, the ethanol is removed by rotary evaporation. 1.0mL of hydrochloric acid solution was added and the pH of the resulting solution was adjusted to 3, whereupon a large amount of yellow solid precipitated. The solid was filtered off with suction and washed three times with 100mL of water. The solid was dissolved in 200mL of ethyl acetate, separated to remove the residual aqueous layer, and dried by adding anhydrous sodium sulfate. Suction filtration and rotary evaporation to remove the solvent gave a pale yellow solid as 5-methoxy-2-methylbenzofuran-3-carboxylic acid (5) in 94% yield. The obtained product is not characterized and is directly put into the next reaction.

4) 0.8g of 5-methoxy-2-methylbenzofuran-3-carboxylic acid (5), 1.44g of p-trifluoromethylaniline (6a), 3.2g of 2- (7-azabenzotriazole) -N, N, N ', N' -tetramethyluronium Hexafluorophosphate (HATU), and 1.2mL of diisopropylethylamine were dissolved in 20mL of anhydrous DMF and reacted at 80 ℃ for 22 hours to obtain a brown solution. After cooling, 100mL of ethyl acetate was added for dilution and washed successively with 50mL of saturated ammonium chloride solution and 50mL of saturated sodium chloride solution. The organic layer was back-extracted with 100mL of saturated sodium chloride solution to remove DMF, which could not be precipitated by recrystallization. After drying and concentration of the solvent, chromatography is carried out with petroleum ether/ethyl acetate (10:1 to 1:1) column, and the crude product obtained contains a portion of 4-trifluoromethylaniline due to the proximity of polarity. Recrystallizing with petroleum ether/ethyl acetate as solvent, standing in a refrigerator at-20 deg.C overnight to obtain white crystal, and recrystallizing the mother liquor to obtain pure product. The total yield of the target product 5-methoxy-2-methyl-N-p-trifluoromethylphenylbenzofuran-3-carboxamide (7a) was 69%.

5) 2.2g of 5-methoxy-2-methyl-N-p-trifluoromethylphenylbenzofuran-3-carboxamide (7a) are dissolved in 20mL of anhydrous dichloromethane. The reaction flask was placed in a-20 ℃ ice salt bath under nitrogen, 3.0mL of boron tribromide was carefully and rapidly added in one portion, and quickly added to an oil bubbler, maintaining an inert atmosphere. Stirring was maintained overnight, during which time the ice salt bath was allowed to slowly return to room temperature. After the reaction was complete, the ice was added back to the water bath and 1.0mL of hydrochloric acid was added dropwise slowly with vigorous stirring. After no bubble was generated, methylene chloride in the reaction mixture was removed by rotary evaporation, ethyl acetate was added (to absorb the boron compound coordinated to the product), water was added, and the layers were separated. The organic phase was washed with saturated sodium bicarbonate solution. After drying and concentration, it was recrystallized directly from ethyl acetate/petroleum ether without column chromatography. This gave 5-hydroxy-2-methyl-N-p-trifluoromethylphenylbenzofuran-3-carboxamide (8a) as an off-white solid (86% yield).

6) 3.3g of 5-hydroxy-2-methyl-N-p-trifluoromethylphenylbenzofuran-3-carboxamide (8a), 1.0mL of 37% aqueous formaldehyde solution and 1.36mL of cyclohexylimine were dissolved in 50mL of absolute ethanol and reacted at 80 ℃ under reflux for 12 hours. TLC detection of the reaction process, after the reaction is finished, concentrating the solvent, and performing chromatography on a silica gel column. The crude product of the target amine is obtained and is sticky. Dissolving the precipitate in ethyl acetate, dropwise adding 0.5mL concentrated hydrochloric acid, concentrating the solvent under heating to separate out a large amount of white precipitate, filtering to obtain solid, washing with excessive ethyl acetate, and removing water in a vacuum drying oven for 4 h. The final 4-cyclohexyliminomethyl substituted benzofuran (9a) was obtained as the hydrochloride in 63% yield as a white solid.

Example 4

The reaction is carried out according to formula II:

1) p-benzoquinone (1) (1.57g), ethyl acetoacetate (2) (2.5g) and anhydrous zinc chloride (2.78g) were dissolved in 250mL of a solvent in the stated order of addition and then reacted at 80 ℃ under reflux for 12 hours. After the reaction, the solvent was removed by rotary evaporation to obtain a black viscous material. After addition of ethyl acetate, the organic phase was separated and the insoluble material was filtered off. The organic phase was concentrated and chromatographed on silica gel column (petroleum ether/ethyl acetate 10:1) to give ethyl 5-hydroxy-2-methylbenzofuran-3-carboxylate (3) as a white powdery solid in 83% yield.

2) Ethyl 5-hydroxy-2-methylbenzofuran-3-carboxylate (3) (15.6g) was weighed out, dissolved in 200mL of anhydrous acetonitrile, and 36g of anhydrous potassium carbonate and 46mL of methyl iodide were added. The reaction was refluxed at 80 ℃ for 12 h. The TLC tracks the reaction progress and finds that partial raw materials still remain unreacted, 18g of anhydrous potassium carbonate and 20mL of methyl iodide are added to continue the reflux reaction for 12h, and the TLC shows that the reaction is complete. The KI formed and the unreacted potassium carbonate solid were filtered, and the filtrate was concentrated and subjected to chromatography on a silica gel column to give a pale yellow liquid as ethyl 5-methoxy-2-methylbenzofuran-3-carboxylate (4) in 78% yield.

3) The obtained ethyl 5-methoxy-2-methylbenzofuran-3-carboxylate (4) (13.4g) was dissolved in 100mL of ethanol, and 100mL of an aqueous solution of 4.46g of potassium hydroxide was added to conduct a reflux reaction at 80 ℃ for 12 hours. After the TLC tracking reaction is finished, the ethanol is removed by rotary evaporation. 1.2mL of hydrochloric acid solution was added and the pH of the resulting solution was adjusted to 3, whereupon a large amount of yellow solid precipitated. The solid was filtered off with suction and washed three times with 100mL of water. The solid was dissolved in 200mL of ethyl acetate, separated to remove the residual aqueous layer, and dried by adding anhydrous sodium sulfate. Suction filtration and rotary evaporation are carried out to remove the solvent, and light yellow solid which is 5-methoxy-2-methylbenzofuran-3-carboxylic acid (5) is finally obtained with the yield of 90%. The obtained product is not characterized and is directly put into the next reaction.

4) 1.0g of 5-methoxy-2-methylbenzofuran-3-carboxylic acid (5), 1.48g of p-methylaniline (6b), 3.26g of 2- (7-azabenzotriazole) -N, N, N ', N' -tetramethyluronium Hexafluorophosphate (HATU), and 1.4mL of diisopropylethylamine were dissolved in 20mL of anhydrous DMF and reacted at 80 ℃ for 22 hours to obtain a brown solution. After cooling, 100mL of ethyl acetate was added for dilution and washed successively with 50mL of saturated ammonium chloride solution and 50mL of saturated sodium chloride solution. The organic layer was back-extracted with 100mL of saturated sodium chloride solution to remove DMF, which could not be precipitated by recrystallization. After drying and concentration of the solvent, chromatography is carried out with petroleum ether/ethyl acetate (10:1 to 1:1) column, and the crude product obtained contains a portion of 4-trifluoromethylaniline due to the proximity of polarity. Recrystallizing with petroleum ether/ethyl acetate as solvent, standing in a refrigerator at-20 deg.C overnight to obtain white crystal, and recrystallizing the mother liquor to obtain pure product. The total yield of the desired product, 5-methoxy-2-methyl-N-p-methylphenylbenzofuran-3-carboxamide (7b), was 72%.

5) 2.4g of 5-methoxy-2-methyl-N-p-methylphenylbenzofuran-3-carboxamide (7b) was dissolved in 20mL of anhydrous dichloromethane. The reaction flask was placed in a-20 ℃ ice salt bath under nitrogen, 3.4mL of boron tribromide was carefully and rapidly added in one portion, and quickly added to an oil bubbler, maintaining an inert atmosphere. Stirring was maintained overnight, during which time the ice salt bath was allowed to slowly return to room temperature. After the reaction was complete, the ice was added back to the water bath and 1.2mL of hydrochloric acid was added dropwise slowly with vigorous stirring. After no bubble was generated, methylene chloride in the reaction mixture was removed by rotary evaporation, ethyl acetate was added (to absorb the boron compound coordinated to the product), water was added, and the layers were separated. The organic phase was washed with saturated sodium bicarbonate solution. After drying and concentration, it was recrystallized directly from ethyl acetate/petroleum ether without column chromatography. This gave 5-hydroxy-2-methyl-N-p-methylphenylbenzofuran-3-carboxamide (8b) as an off-white solid (88% yield).

6) 3.5g of 5-hydroxy-2-methyl-N-p-methylphenylbenzofuran-3-carboxamide (8), 1.2mL of 37% aqueous formaldehyde solution and 1.4mL of cyclohexylimine were dissolved in 50mL of absolute ethanol and reacted at 80 ℃ under reflux for 12 hours. TLC detection of the reaction process, after the reaction is finished, concentrating the solvent, and performing chromatography on a silica gel column. The crude product of the target amine is obtained and is sticky. Dissolving the precipitate in ethyl acetate, dropwise adding 0.7mL concentrated hydrochloric acid, concentrating the solvent under heating to separate out a large amount of white precipitate, filtering to obtain solid, washing with excessive ethyl acetate, and removing water in a vacuum drying oven for 4 h. 4-Cyclohexaneiminomethyl-substituted benzofuran (9b) was obtained as the hydrochloride salt in 62% yield.

Example 5

The reaction is carried out according to formula III:

1) p-benzoquinone (1) (1.6g), ethyl acetoacetate (2) (2.8g) and anhydrous zinc chloride (2.82g) were dissolved in 250mL of a solvent in the stated order of addition and then reacted at 80 ℃ under reflux for 12 hours. After the reaction, the solvent was removed by rotary evaporation to obtain a black viscous material. After addition of ethyl acetate, the organic phase was separated and the insoluble material was filtered off. The organic phase was concentrated and chromatographed on silica gel column (petroleum ether/ethyl acetate 10:1) to give 5-hydroxy-2-methylbenzofuran-3-carboxylic acid ethyl ester (3) as a white powdery solid.

2) Ethyl 5-hydroxy-2-methylbenzofuran-3-carboxylate (3) (15.7g) was weighed out, dissolved in 200mL of anhydrous acetonitrile, and 39g of anhydrous potassium carbonate and 48mL of methyl iodide were added. The reaction was refluxed at 80 ℃ for 12 h. And (3) tracking the reaction progress by TLC to find that partial raw materials are still not reacted completely, supplementing 20g of anhydrous potassium carbonate and 24mL of methyl iodide, and continuing refluxing for 12h, wherein the TLC shows that the reaction is complete. The KI formed and the unreacted potassium carbonate solid were filtered, and the filtrate was concentrated and subjected to chromatography on a silica gel column to give a pale yellow liquid as ethyl 5-methoxy-2-methylbenzofuran-3-carboxylate (4) in 77% yield.

3) The obtained ethyl 5-methoxy-2-methylbenzofuran-3-carboxylate (4) (13.8g) was dissolved in 100mL of ethanol, and 100mL of an aqueous solution of 4.5g of potassium hydroxide was added to conduct a reflux reaction at 80 ℃ for 12 hours. After the TLC tracking reaction is finished, the ethanol is removed by rotary evaporation. 1.5mL of hydrochloric acid solution was added and the pH of the resulting solution was adjusted to 3, whereupon a large amount of yellow solid precipitated. The solid was filtered off with suction and washed three times with 100mL of water. The solid was dissolved in 200mL of ethyl acetate, separated to remove the residual aqueous layer, and dried by adding anhydrous sodium sulfate. Suction filtration and rotary evaporation to remove the solvent to finally obtain a light yellow solid which is 5-methoxy-2-methylbenzofuran-3-carboxylic acid (5) with a yield of 89%. The obtained product is not characterized and is directly put into the next reaction.

4) 1.4g of 5-methoxy-2-methylbenzofuran-3-carboxylic acid (5), 1.5g of m-methylaniline (6c), 3.3g of 2- (7-azabenzotriazole) -N, N, N ', N' -tetramethyluronium Hexafluorophosphate (HATU), and 1.6mL of diisopropylethylamine were dissolved in 20mL of anhydrous DMF and reacted at 80 ℃ for 22h to give a brown solution. After cooling, 100mL of ethyl acetate was added for dilution and washed successively with 50mL of saturated ammonium chloride solution and 50mL of saturated sodium chloride solution. The organic layer was back-extracted with 100mL of saturated sodium chloride solution to remove DMF, which could not be precipitated by recrystallization. After drying and concentration of the solvent, chromatography is carried out with petroleum ether/ethyl acetate (10:1 to 1:1) column, and the crude product obtained contains a portion of 4-trifluoromethylaniline due to the proximity of polarity. Recrystallizing with petroleum ether/ethyl acetate as solvent, standing in a refrigerator at-20 deg.C overnight to obtain white crystal, and recrystallizing the mother liquor to obtain pure product. The total yield of the desired product, 5-methoxy-2-methyl-N-m-methylphenylbenzofuran-3-carboxamide (7c), was 53%.

5) 2.5g of 5-methoxy-2-methyl-N-m-methylphenylbenzofuran-3-carboxamide (7c) are dissolved in 20mL of anhydrous dichloromethane. The reaction flask was placed in a-20 ℃ ice salt bath under nitrogen, 3.8mL of boron tribromide was carefully and rapidly added in one portion, and quickly added to an oil bubbler, maintaining an inert atmosphere. Stirring was maintained overnight, during which time the ice salt bath was allowed to slowly return to room temperature. After the reaction was complete, the ice was added back to the water bath and 1.5mL of hydrochloric acid was added slowly dropwise with vigorous stirring. After no bubble was generated, methylene chloride in the reaction mixture was removed by rotary evaporation, ethyl acetate was added (to absorb the boron compound coordinated to the product), water was added, and the layers were separated. The organic phase was washed with saturated sodium bicarbonate solution. After drying and concentration, it was recrystallized directly from ethyl acetate/petroleum ether without column chromatography. This gave 5-hydroxy-2-methyl-N-m-methylphenylbenzofuran-3-carboxamide (8c) as an off-white solid (87% yield).

6) 3.6g of 5-hydroxy-2-methyl-N-p-trifluoromethylphenylbenzofuran-3-carboxamide (8c), 1.5mL of 37% aqueous formaldehyde solution, and 1.8mL of cyclohexylimine were dissolved in 50mL of absolute ethanol and reacted at 80 ℃ under reflux for 12 hours. TLC detection of the reaction process, after the reaction is finished, concentrating the solvent, and performing chromatography on a silica gel column. The crude product of the target amine is obtained and is sticky. Dissolving the precipitate in ethyl acetate, dropwise adding 1mL concentrated hydrochloric acid, concentrating the solvent under heating condition to precipitate a large amount of white precipitate, filtering to obtain solid, washing with excessive ethyl acetate, and removing water in a vacuum drying oven for 4 h. The final 4-cyclohexyliminomethyl substituted benzofuran (9c) was obtained as the hydrochloride in 41% yield as a white solid.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.