PROCESS FOR PREPARING 4-OXO-4,5,6,7-TETRAHYDROBENZOFURAN DERIVATIVE

Abstract: A 4-oxo-4,5,6,7-tetrahydrobenzofuran derivative is pre­ pared by reacting a 1,3-cyclohexanedione derivative with chloroacetaldehyde in the presence of a base while maintain­ ing the reaction mixture at a pH of from 4 to 10, and treating the reaction mixture with an acid. The 4-oxo-4,5,6,7-­ tetrahydrobenzofuran derivatives are useful as an intermedi­ ate for synthesis of various kinds of drugs.

Description: The present invention relates to a process for preparing 4-oxo-4,5,6,7-tetrahydrobenzofuran derivatives. More specifically, the present invention relates to a process for preparing 4-oxo-4,5,6,7-tetrahydrobenzofuran derivatives of the formula (I): wherein R and R¹ are a hydrogen atom or an alkyl group. The benzofuran derivatives of the formula (I) are useful as an intermediate for synthesis of drugs, particularly as an intermediate for synthesis of 4-hydroxyindole which is a key intemediate for synthesis of Pindolol, or as an intermediate for synthesis of various kinds 4-substituted indole drugs (K. Saemeli: Helv. Physiol. Acta, 25 , 221 (1967): Japanese Patent Unexamined Publication No. 103160/1981). As a process for preparing 4-oxo-4,5,6,7-tetrahydrobenzuforan derivatives, there hitherto has been known Feist-Benary synthesis. That is, a process in which 1,3-cyclohexanedione is condensed with chloroacetoaldehyde in the presence of a base (E. Bisagni et al.: Bull. Soc. Chim. Fr., 4041(1971)). The above-mentioned method, however, is not suitable for the industrial production because of low yield of the desired 4-oxo-4,5,6,7-tetrahydrobenzuforan derivative, as is utmost about 40%. It is an object of the present invention to provide a process for preparing 4-oxo-4,5,6,7-tetrahydrobenzofuran derivatives. Another object of the present invention is to provide a process in which 4-oxo-4,5,6,7-tetrahydrobenzofuran derivatives can be easily prepared in a high yield by condensing a 1,3-cyclohexanedione derivative with chloroacetoaldehyde. It has now been found that it is important to adjust the reaction condition for condensing a 1,3-cyclohexanedione derivative and chloroacetoaldehyde so as to maintain the balance between the desired reaction and the dissociation equilibrium between the polymer and monomer of chloroacetaldehyde in order to apply the Freist-Benary synthesis to the above reaction, since chloroacetaldehyde is relatively hard to exist in the reaction mixture as a monomer. In fact, when the reaction mixture is considerably strong acid (1,3-cyclohexanedione derivatives and chloroacetaldehyde are strong acids per se) or strong base, a condensed product is produced from two moles of 1,3-cyclohexanedione derivative and one more of chloroacetaldehyde in a considerably large amount, particularly under a strong basic condition, a product which is partially deprived of hydrogen chloride is produced from the chloroacetaldehyde polymer. In accordance with the present invention, there can be provided a process for preparing a 4-oxo-4,5,6,7-tetrahydrobenzofuran derivative of the formula (I): wherein R and R¹ are a hydrogen atom or an alkyl group, by reacting a 1,3-cyclohexanedione derivative of the formula (II): wherein R and R¹ are as defined above, with chloroacetaldehyde in the presence of a base characterized by a) mixing a 1,3-cyclohexanedione derivative and chloroacetaldehyde in the presence of a base, said base being selected from the group consisting of triethylamine, sodium hydrogencarbonate, potassium carbonate and sodium hydroxide, and being employed in from 1 to 1.2 equimolar amount to the used 1,3-cyclohexanedione derivative, b) maintaining the reaction mixture at a pH of from 5.4 to 10 throughout the reaction, and c) after the completion of the reaction, dehydrating the compound (IV) formed: wherein R and R¹ are as defined above, by acidifying the resultant reaction mixture. Both the 1,3-cyclohexanedione derivatives of the formula (II) and chloroacetaldehyde being the starting materials of the present invention can be easily obtained by industrial processes. Though the process of the present invention preferably carried out in water for smoothly proceeding the reaction, an organic solvent such as ethyl acetate, dichloromethane or toluene can be used in combination with water when the reaction materials and the product are slightly soluble in water. The use of an alcoholic solvent such as methanol having a nucleophilicity is not suitable because such a solvent causes a side reaction. The reaction is easily proceeded at a temperature of from -20° to 100°C, preferably from -10°C to a room temperature for producing the desired compound in good efficiency. After completion of the considering reaction of a 1,3-cyclohexanedione derivative and chloroacetaldehyde, it is necessary to treat the reaction mixture with an acid for dehydrating the following compound (IV), because the reaction is terminated at the following step under the above reaction conditions: wherein R and R¹ are as defined above. Examples of the acid are, for instance, inorganic acids such as sulfuric acid, hydrochloric acid, organic acids such as sulfonic acid, which are usually utilized in the dehydration reaction. The compound (I) can be easily converted into a 4-oxo-4,5,6,7-tetrahydroindole derivative of the formula: by reacting with ammonia. The present invention is more specifically described and explained by means of the following Examples and Reference Example, in which all % are by weight unless otherwise noted. The Reference Example is to illustrate the preparation of 4-oxo-4,5,6,7-tetrahydroindole from 4-oxo-4,5,6,7-tetrahydrobenzofuran. It is to be understood that the present invention is not limited to the Examples. Examples 1 to 5 and Comparative Examples 1 to 8 To 5 ml of water were added 1.12 g (10 mmoles) of 1,3-cyclohexanedione and the each base shown in Table 1, and then 2 ml of 40% aqueous solution of chloroacetaldehyde was added thereto. The resulting mixture was stirred at a room temperature for 2 hours. To the reaction mixture was added about 10 ml of ethyl acetate, and then the reaction mixture was acidified with 0.5 to 1 ml of sulfuric acid and stirred for 30 minutes. The resulting ethyl acetate layer was analyzed by gas-liquid chromatography (hereinafter referred to as "GLC") (SE30 10%, 1.2 m x 3 mm glass column, 130°C) using p-dimethoxybenzene as an internal standard. The obtained each result is shown in Table 1. It was proved from the results of the GLC that 4-oxo-4,5,6,7-tetrahydrobenzofuran was produced in a yield shown in Table 1, in each Example. Comparative Example 1 was carried out in the absence of a base. Example 6 To a mixture of 1.12 g (10 mmoles) of 1,3-cyclohexanedione and 8 ml of water was added 1.38 g (10 mmoles) of potassium carbonate, and then 2 ml of 40% aqueous solution of chloroacetaldehyde was added thereto. The resulting mixture was stirred at a room temperature for 45 hours. The reaction mixture was maintained at a pH of from 7.75 to 9.50 throughout the reaction. After completing the reaction, the obtained reaction mixture was treated and analyzed in the same manner as in Example 1. It was proved from the results of the analysis that 4-oxo-4,5,6,7-tetrahydrobenzofuran was produced in a 68% yield. Example 7 To a mixture of 80 ml of water and 20 ml of 40% aqueous solution of chloroacetaldehyde was added 10.0 g (119 mmoles) of sodium hydrogencarbonate while cooling with ice. To the resulting reaction mixture was added dropwise 90 ml of aqueous solution containing 11.2 g (100 mmoles) of 1,3-cyclohexanedione while cooling with ice at a rate of 0.4 ml/minute. The reaction mixture was maintained at a pH of from 9 to 6 throughout the reaction. After completing the dropping, the reaction mixture was stirred at a room temperature overnight. To the resulting reaction mixture was added about 100 ml of ethyl acetate, and then the reaction mixture was acidified (pH < 1) with sulfuric acid and stirred for about one hour. The ethyl acetate layer was separated, washed with an aqueous solution of potassium carbonate, and dried on magnesium sulfate. After distilling away the ethyl acetate, the obtained residue was distilled under a reduced pressure to give 10.3 g (yield: 76%) of 4-oxo-4,5,6,7-tetrahydrobenzofuran being a colorless oily material (boiling point: 66°C/1,33.10⁻³ bar (1 torr). Example 8 To a mixture of 10 ml of ethyl acetate, 2 ml of 40% aqueous solution of chloroacetaldehyde and about 3 ml of water was added 1.0 g (12 mmoles) of sodium hydrogencarbonate while cooling with ice, and then the resulting mixture was stirred. To the reaction mixture was added dropwise 5 ml of aqueous solution containing 1.12 g of 1,3-cyclohexanedione while cooling with ice at a rate of 0.05 ml/minute. The reaction mixture was maintained at a pH of from 6.2 to 8.7 throughout the reaction. After completing the dropping, the reaction mixture was stirred at a room temperature overnight, and then acidified with sulfuric acid. After stirring the mixture for one hour, the ethyl acetate layer was separated, washed with an aqueous solution of potassium carbonate for removing the unreacted 1,3-cyclohexanedione, and then dried on magnesium sulfate. After distilling away the solvent, the residue was applied to a column of silica gel and eluted with dichloromethane to give 1.09 g (yield: 80%) of 4-oxo-4,5,6,7-tetrahydrobenzofuran. Example 9 To a mixture of 24 ml of water and 6 ml of 40% aqueous solution of chloroacetaldehyde was added 0.7 g (8 mmoles) of sodium hydrogencarbonate while cooling with ice. To the reaction mixture were added dropwise 4.2 g (30 mmoles) of 5,5-dimethyl-1,3-cyclohexanedione and 40 ml of aqueous solution containing 2.3 g (37 mmoles) of sodium hydrogencarbonate while cooling with ice at a rate of 0.4 ml/minute. The reaction mixture was maintained at a pH of from 5.7 to 8.0 throughout the reaction. After completing the dropping, the reaction mixture was stirred at a room temperature overnight, and then treated in the same manne as in Example 1 to give 2.36 g (yield: 48.2%) of 4-oxo--6,6-dimethyl-4,5,6,7-tetrahydrobenzofuran being a colorless oily material (boiling point: 78 C/0.93.10⁻³ bar (0.7 mmHg). Reference Example To a mixture of 3 ml of ethanol and 7 ml of 29% aqueous ammonia was added 1.0 g of 4-oxo-4,5,6,7-tetrahydrobenzofuran, and then the mixture was subjected to reaction in a sealed tube at 150 C for 12 hours. After completing the reaction, the reaction mixture was concentrated. The resulting residue was applied to a column of silica gel and eluted with a mixed solvent of acetone and ethyl acetate to give 950 mg (yield: 96%) of 4-oxo-4,5,6,7-tetrahydroindole being a light yettowish crystal.

Claims: 1. A process for preparing a 4-oxo-4,5,6,7-tetrahydrobenzofuran derivative of the formula (I): wherein R and R¹ are a hydrogen atom or an alkyl group, by reacting 1,3-cyclohexanedione derivative of the formula (II): wherein R and R¹ are as defined above, with chloroacetaldehyde in the presence of a base, characterized by a) mixing a 1,3-cyclohexanedione derivative and chloroacetaldehyde in the presence of a base, said base being selected from the group consisting of triethylamine, sodium hydrogencarbonate, potassium carbonate and sodium hydroxide, and being employed in from 1 to 1.2 equimolar amount to the used 1,3-cyclohexanedione derivative, b) maintaining the reaction mixture at a pH of from 5.4 to 10 throughout the reaction, and c) after the completion of the reaction, dehydrating the compound (IV) formed: wherein R and R¹ are as defined above, by acidifying the resultant reaction mixture.

Inventors: MATSUMOTO, MASAKATSU, WATANABE, NOBUKO
Applicants: SAGAMI CHEMICAL RESEARCH CENTER
Application year: 1983
Main classification: C07D307
IPC codes: C07D307