Process for the preparation of lignin analogues and starting materials therefor

Abstract: A process for preparing a compound represented by the formula wherein R¹ is a lower alkyl, cycloalkyl, cycloalkyl-lower alkyl, aryl or aralkyl group which is optionally substituted; R² is a group represented by the formula: -COOR': (wherein R' is a lower alkyl or aralkyl which is optionally substituted), lower alkyl, or halogenated lower alkyl, or, R¹ and R², together with adjacent carbonyl group, form a cyclohexanone ring: R³ is a phenyl group optionally being substituted; and, ring A is a benzene nucleus which is optionally substituted, or a heterocyclic ring containing S or O optionally being substituted; which process is characterized by that a lactone compound represented by the formula: in which R³ and ring A are as defined above, is allowed to react with a compound of a formula: in which R¹ and R² are as defined above in the presence of a base, and then the resulting compound is subject to dehydration and compounds used in the process.

Description: The present invention relates to a process for the preparation of a compound (hereinafter referred as Compound (I) of the present invention) represented by Formula (I): wherein R 1 is a lower alkyl, cycloalkyl, cycloalkyl-lower alkyl, aryl or aralkyl group which is optionally substituted, R 2 is a group represented by the formula: -COOR': (wherein R' is a lower alkyl or aralkyl which is optionally substituted), lower alkyl or halogenated lower alkyl, or, R 1 and R 2 , together with adjacent carbonyl group, form a cyclohexanone ring represented by the formula: R 3 is a phenyl group optionally being substituted, and, ring A is a benzene nucleus which is optionally substituted, or a heterocyclic ring containing S or O optionally being substituted, The present invention also provides starting compounds for the process. Hyperlipemia is believed to be one of the major causes of a geriatric disease arteriosclerosis. Among the hyperlipemic diseases, hypercholesterolemia is particularly in close relationship with arteriosclerosis. Cholesterol is present in blood in either one of the forms of very low density lipoprotein (hereinafter referred as VLDL), low density lipoprotein (LDL) and high density lipoprotein (HDL). VLDL and LDL enhance deposition of cholesterol in an arterial wall whereby causing arteriosclerosis, while HDL prevents the deposition and exhibits therapeutic and prophylactic effects against arteriosclerosis, as reported in Annals of Internal Medicine, 90 , 85, (1979). Accordingly, an anti-hyperlipemic agent capable of reducing selectively VLDL and LDL cholesterols is desired in the field of treatment and prophylaxis of arteriosclerosis. Drugs directed to the purpose described above were disclosed, for example, in Japanese Patent Publication Nos. H3-72422, H3-157351, H2-72136 and H1-135766. Among factors causing atherosclerosis which is most significant in arteriosclerotic diseases, the behavior of LDL cholesterol in blood is quite important. Especially, permeation of LDL into arterial walls and incorporation of LDL by macrophages in the wall, and resulting formation of foam cells and accumulation of cholesterols in intima and blood vessel failures are very important. It is believed that oxidized LDLs are exclusively incorporated into macrophages (D. Steinberg, S. Parthasarathy, T.E.Carew, J.C.Khoo and J.L.Witztum, N.Engl.J. Med., 320 , 915 (1989)). Thus, an anti-hyperlipemic agent having anti-oxidizing effect on LDLs in addition to the ability of reducing VLDL and LDL cholesterols selectively as mentioned above is desirable. However, no such agents have been reported. Compounds (I) and pharmaceutically acceptable salts thereof have anti-oxidizing effect on LDLs in addition to the ability of reducing VLDL and LDL cholesterols selectively. Compounds (I) can readily be converted into desirable salts by a known manner. Pharmaceutically acceptable salts of Compounds (I) include alkaline metal salts such as sodium and potassium salts, alkaline earth metal salts such as calcium and magnesium salts, and quaternary ammonium salts such as tetramethylammoniumsalt. Throughout the specification, the terms have the means as described below. In the definition of group R 1 in Formula (I), "a lower alkyl group which is optionally substituted" means a straight or branched C 1 -C 6 alkyl which may have one or more substituents. "A straight or branched C 1 -C 6 alkyl" includes methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, t-butyl, n-pentyl, i-pentyl, neopentyl, s-pentyl, t-pentyl, l-ethylpropyl, n-hexyl, neohexyl, i-hexyl, s-hexyl and t-hexyl. The substituent may be hydroxyl, halogen atom (F, Cl, Br, I), amino, cyano, nitro, nitroso, hydrazino, hydroxyamino, thiol and lower alkoxy groups. The lower alkoxy groups include methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy, s-butoxy, t-butoxy, n-pentyloxy, i-pentyloxy, neopentyloxy, s-pentyloxy, t-pentyloxy, n-hexyloxy, neohexyloxy, i-hexyloxy, s-hexyloxy and t-hexyloxy. "A cycloalkyl which is optionally substituted" means a C 3 -C 7 cycloalkyl group which may have one or more substituents. The C 3 -C 7 cycloalkyl includes cyclopropane, cyclobutane, cyclopentane, cyclohexane and cycloheptane. The substituent may be hydroxyl, halogen atom (F, Cl, Br, I), amino, cyano, nitro, nitroso, hydrazino, hydroxyamino, thiol and lower alkoxy groups, and the lower alkoxy groups include methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy, s-butoxy, t-butoxy, n-pentyloxy, i-pentyloxy, neopentyloxy, s-pentyloxy, t-pentyloxy, n-hexyloxy, neohexyloxy, i-hexyloxy, s-hexyloxy and t-hexyloxy. "A cycloalkyl-lower alkyl which is optionally substituted" means a lower alkyl defined above which is substituted with a cycloalkyl which may optionally be substituted as defined above, and includes cyclopropylmethyl, cyclobutylpropyl, cyclopentylethyl, cyclohexylpropyl and cyclohexylmethyl. In the definition of group R 1 , "an aryl group which is optionally substituted" means a phenyl or naphthyl which may have one or more substituents. The substituents may be lower alkyl groups listed above, lower alkoxy groups listed above, hydroxyl, halogen atom (F, Cl, Br, I), haloalkyl such as trifluoromethyl, amino, cyano, nitro, nitroso, hydrazino, hydroxyamino and thiol groups. "An aralkyl group which is optionally substituted" means a lower alkyl defined above which is substituted with an aryl which may optionally be substituted as defined above, and includes benzyl, p-methoxybenzyl, phenetyl phenylpropyl and naphthylmethyl. In the definition of group R 2 in Formula (I), "a group represented by the formula: -COOR' wherein R' is a lower alkyl or aralkyl which is optionally substituted" means a carboxylate ester residue containing an alkyl or aralkyl group which may be substituted. "A halogenated lower alkyl group" in group R 2 means a lower alkyl defined above which is substituted by a halogen atom, such as trifluoromethyl (-CF 3 ), pentafluoroethyl and chloroethyl. In the definition of group R 3 , "a phenyl group which is optionally substituted" means a phenyl group optionally having one or more substituents, or a phenyl-containing condensed ring such as 3, 4-ethylenedioxyphenyl group represented by the formula: The substituents may be lower alkyl groups listed above, lower alkoxy groups listed above, hydroxyl, halogen atom (F, Cl, Br, I), amino, cyano, nitro, nitroso, hydrazino, hydroxyamino and thiol groups. In the definition of ring A, "a benzene nucleus which is optionally substituted" means a benzene nucleus which may have one or more substituents, or a benzene-containing condensed ring represented by the formula: The substituents may be lower alkyl groups listed above, lower alkoxy groups listed above, hydroxyl, halogen atom (F, Cl, Br, I), amino, cyano, nitro, nitroso, hydrazino, hydroxyamino and thiol groups. In the definition of ring A, "a heterocyclic ring containing S or O optionally being substituted" means a 5 or 6 membered aromatic heterocyclic ring which may have one or more substituents and which contains one or more of S or O atoms in the ring. Such aromatic heterocyclic ring may include furan and thiophene. The substituents may be ones selected from the group of lower alkyl groups listed above, lower alkoxy groups listed above, hydroxyl, halogen atom (F, Cl, Br, I), amino, cyano, nitro, nitroso, hydrazino, hydroxyamino, thiol and C 1 -C 3 alkylenedioxy groups. Journal of Organic Chemistry, Vol. 22, No. 3, pages 308-312 describes the preparation of various alkyl 4-oxo-2-alkenoates as potential antimicrobial agents. "SYNTHESIS" Journal of Synthetic Organic Chemistry, No. 5, May 1986, pages 378 to 379 also describes various methyl trans-4-oxo-2-alkenoates. "SYNTHESIS" Journal of Synthetic Organic Chemistry, No. 10, October 1987, pages 943 to 944 describes 3-(3,4-dimethoxyphenyl)-4,5-dimethoxy-1(3H)-isobenzofuranone. According to the present invention there is provided a process for preparing a compound represented by the formula (I): wherein R 1 is a C 1 -C 6 alkyl, cycloalkyl, cycloalkyl-C 1 -C 6 alkyl, aryl or aralkyl group which is optionally substituted. R 2 is a group represented by the formula: -COOR' (wherein R' is a C 1 -C 6 alkyl or aralkyl which is optionally substituted), C 1 -C 6 alkyl, or halogenated C 1 -C 6 alkyl, or, R 1 and R 2 , together with adjacent carbonyl group, form a cyclohexanone ring represented by the formula: R 3 is a phenyl group optionally being substituted, and, ring A is a benzene nucleus which is optionally substituted, or a heterocyclic ring containing S or O optionally being substituted, which process is characterized by that a lactone compound represented by the formula (VI): in which R 3 and ring A are as defined above, is allowed to react with a compound of a formula (VII): in which R 1 and R 2 are as defined above in the presence of a base, and then the resulting compound is subject to dehydration. The present invention further provides the above process wherein the compound is represented by the formula (I'): in which R 1 is ethyl, 1-ethylpropyl, or 2-ethylbutyl; R 12 , R 13 and R 14 are methoxy; R 15 and R 16 are methyl; and R 17 is C 1 -C 6 alkyl; which process is characterized in that a lactone compound represented by the formula (VI'); in which R 12 ,R 13 ,R 14 , R 15 , and R 16 are defined above, is allowed to react with a compound of a formula (VII'); in which R 1 and R 17 are as defined above in the presence of a base, and then the resulting compound is subjected to dehydration in the presence of an acid. The invention also provides a starting compound for the above process which is a compound of the formula (VI'); in which R 12 , R 13 and R 14 are methoxy; and R 15 and R 16 are methyl. Also provided is a starting compound of the formula (VII'); in which R 1 is ethyl, 1-ethylpropyl or 2-ethylbutyl; and R 17 is methyl. The method of the present invention is shown in the following reaction scheme. Scheme of steps In the first step, a lactone [VI] and an unsaturated ketone [VII] are subjected to Michael addition and then intramolecular condensation (in situ) is effected to yield Compound (VIII). Although the ratio of Compound (VI) to Compound (VII) is not particularly limited, Compound (VII) is used in excess of Compound (VI), preferably in the ratio of 1 : 1 to 1 : 2. The solvent includes ethers such as tetrahydrofuran, diethylether, dimethoxyethane and dioxane, aromatic solvents such as benzene, toluene and xylene, hydrocarbons such as n-hexane, n-pentane and n-heptane, halogenated hydrocarbons such as dichloromethane and dichloroethane, amides such as N, N-dimethylformamide and hexamethylphosphoric triamide, which may be employed independently or in a mixture. Preferable solvents are tetrahydrofuran, dichloromethane, dichloroethane, N, N-dimethylformamide and hexamethylphosphoric triamide. The bases include dialkyl metal amides such as lithium diisopropylamide, sodium dicyclohexylamide and potassium diethylamide, bis(trialkylsilyl) metal amides such as lithium bis(trimethylsilyl)amide, sodium bis(trimethylsilyl)amides and potassium bis(dimethylphenylsilyl)amide as well as alkoxides such as potassium t-butoxide. A preferable base is lithium bis(trimethylsilyl)amide. The reaction is usually completed within a period from several minutes to several hours at about -100°C to about 100°C, preferably at about -80°C to room temperature. In the second step, Compound (VIII) is dehydrated by acid treatment to yield Compound (I). The reaction solvent includes aromatic solvents such as benzene, toluene and xylene as well as halogenated hydrocarbons such as dichloromethane and chloroform. The acids is, for example, protic acids such as hydrochloric acid, sulfuric acid, trifluoroacetic acid, and sulfonic acids (methanesulfonic acid, p-toluenesulfonic acid) and Lewis acids such as boron trifluoride and titanium tetrachloride, particularly preferred is boron trifluoride. Although the amount employed is not particularly limited, an amount of 1 to 2 equivalents is preferable. The reaction is usually completed within a period from several minutes to several ten hours at -70°C to 100°C, preferably at -20°C to room temperature. The methods of preparation of the starting materials useful in the preparation of the compounds by the process of the present invention are described below, but any other methods can also be employed to obtain each of the starting materials. Starting materials VI and VII can be prepared, for example, by the methods employed in Preparations 1 to 11 described below. The procedure of the process of the present invention is described below. First, the starting materials shown below were prepared. Preparation 1 Synthesis of 3-(3,4-dimethoxyphenyl)-4,5,6-trimethoxy-1(3H)-isobenzofuranone: VI-1 Step-1 (4,4-Dimethyl-2-(3,4,5-trimethoxyphenyl)-2-oxazoline: 18) A solution of 16.2 g (70 mmol) of 3,4,5-trimethoxybenzoyl chloride (17) in 40 ml of dry methylene chloride was added dropwise to a solution of 12.5 g (140 mmol) of 2-amino-2-methyl-1-propanol in 50 ml of dry methylene chloride under cooling in an ice-bath over 30 minutes. After additional stirring for 45 minutes, the reaction mixture was filtered through a glass filter. The filter cake was washed with methylene chloride. The filtrate and the washing were combined and concentrated under reduced pressure. The residue was dissolved in 30 ml of toluene, and then 6.64 ml (91.0 mmol) of thionyl chloride was added dropwise under cooling in an ice-bath. The mixture was allowed to warm to room temperature while being stirred for 45 minutes. To the reaction mixture was added ice (20 g) and aqueous sodium hydroxide (18 g of NaOH in 60 ml of water) and the mixture was extracted with toluene. The extract was washed with water and brine, and dried over anhydrous magnesium sulfate. After concentration under reduced pressure, the residue was crystallized from 70 ml of n-hexane to obtain 16.8 g (90.6%) of desired compound 18. mp: 87-89°C 1 H-NMR:δ(CDCl 3 ) 1.39(6H,s) 3.88(3H,s) 3.91(6H,s) 4.10(2H,s) 7.20(2H,s) ppm. Step-2 (Synthesis of VI-1) To a solution of compound 18 (16.8 g, 63.4 mmol) in 100 ml of dry THF, which was cooled with refrigerant at -30°C, 40.0 ml of 1.68N n-BuLi in n-hexane was added dropwise over 15 minutes under nitrogen flow. After stirring for 45 minutes, the mixture was cooled to -78°C, and a solution of 11.6 g (69.7 mmol) of 3,4-dimethoxybenzaldehyde in 30 ml of dry THF was added dropwise thereto. The mixture was allowed to warm to room temperature while being stirred for 1 hour. After addition of 20 ml of saturated aqueous ammonium chloride and 20 ml of water, the mixture was extracted with ethylacetate. The extract was washed with water and brine, and dried over anhydrous magnesium sulfate. After concentration under reduced pressure, the residue was dissolved in 70 ml of 10% sulfuric acid, and heated under reflux for 30 minutes. To the reaction mixture was added ice and water, and the mixture was extracted with methylene chloride. The extract was dried over anhydrous magnesium sulfate. After concentration under reduced pressure, the residue was crystallized from 80 ml of methanol to obtain 20.6 g (90.4%) of desired compound (VI-1). mp: 141-142°C 1 H-NMR:δ(CDCl 3 ) 3.52(3H,s) 3.83(3H,s) 3.89(3H,s) 3.92(3H,s) 3.95(3H,s) 6.32(1H,s) 6.72(1H,s) 6.86(2H,s) 7.21(1H,s) ppm. Preparations 2 - 5 The reactions were conducted similarly to that of Preparation 1 to obtain compounds VI-5, 6, 7 and 8, whose yields and physical properties are shown below. Preparation 2 (VI-5) ; Yield: 80% (through 2 steps) mp: 107-108°C (ether) 1 H-NMR:δ(CDCl 3 ) 3.60(3H,s) 3.92(3H,s) 3.95(3H,s) 6.29(1H,s) 7.02-7.18(3H,m) 7.20(1H,s) ppm. Preparation 3 (VI-6) ; Yield: 79% (through 2 steps) mp: 125-127°C (ether) 1 H-NMR:δ(CDCl 3 ) 3.62(3H,s) 3.91(3H,s) 3.95(3H,s) 6.28(1H,s) 7.15(1H,dd,J=8.4Hz,2.2Hz) 7.20(1H,s) 7.39(1H,d,J=2.2Hz) 7.45(1H,d,J=8.4Hz) ppm. Preparation 4 (VI-7) ; Yield: 88% (through 2 steps) mp: 119-121°C (ether) 1 H-NMR:δ(CDCl 3 ) 3.56(3H,s) 3.92(3H,s) 3.94(3H,s) 4.24(4H,s) 6.25(1H,s) 6.72-6.88(3H,m) 7.19(1H,s) ppm. Preparation 5 (VI-8) ; Yield: 82% (through 2 steps) mp: 121-122.5°C (ether) 1 H-NMR:δ(CDCl 3 ) 3.56(3H,s) 3.89(3H,s) 3.92(3H,s) 3.95(3H,s) 6.28(1H,s) 6.89-7.09(3H,m) 7.20(1H,s) ppm. Preparation 6 Synthesis of 4,6-dihydro-6-(3,4-dimethoxyphenyl)-3-methyl-4-oxothieno[2,3-c]furan: VI-2 Step-1 (4-Methylthiophen-3-carboxylic acid: 19) A mixture of 8.30 g (67.4 mmol) of 3-cyano-4-methylthiophene [J. W. Terpstra and A. M. von Leusen, J. Org. Chem., 51 , 230 (1986)] and 83 ml of concentrated hydrochloric acid was heated under reflux for 40 hours. After cooling, the mixture was extracted with ethyl acetate. The extract was washed with water and brine, and then dried over anhydrous magnesium sulfate. The solvent was distilled off under reduced pressure and the residue was washed with petroleum ether to obtain 6.40 g of desired compound 19. The solvent in the washings was distilled off, and to the residue was added 5 ml of water, 5 ml of acetic acid and 5 ml of conc. sulfuric acid, and then the mixture was stirred for 3.5 hours at 135°C. After cooling, the mixture was extracted with ether. The ether layer was extracted with 10% aqueous sodium hydroxide. The aqueous layer was acidified with dilute hydrochloric acid, and extracted again with ether. The extract was washed with water and brine, and dried over anhydrous magnesium sulfate. The solvent was distilled off under reduced pressure and the residue was washed with petroleum ether to obtain 1.57 g of desired compound 19 (total yield: 83%). mp: 137-138°C 1 H-NMR:δ(CDCl 3 ) 2.49(3H,d,J=0.8Hz) 6.94-6.98(1H,m) 8.24(1H,d,J=3.6Hz) ppm. Step-2 (VI-2) To a solution of 11.6 g (114 mmol) of diisopropylamine in 150 ml of dry THF cooled at -78°C, 68.9 ml of 1.66M n-BuLi in n-hexane (114 mmol) was added dropwise under nitrogen flow. After addition, the mixture was stirred at 0°C for additional 30 minutes, and then re-cooled to -78°C. To this cooled solution, a solution of 4-methyl-3-thiophenecarboxylic acid 19 obtained above (7.40 g, 52.0 mmol) in 50 ml of dry THF was added dropwise, and the mixture was stirred at 0°C for 30 minutes, and then cooled again to -78°C. To the cooled solution, a solution of 8.65 g (52.1 mmol) of 3,4-dimethoxybenzaldehyde in 50 ml of dry THF was added dropwise over 10 minutes. After addition, the mixture was stirred for 100 minutes at the same temperature. The reaction mixture was acidified by addition of ice and 6N HCl, and then extracted with ethyl acetate. The extract was washed with water and brine, and dried over anhydrous magnesium sulfate. The solvent was distilled off under reduced pressure. The residue was dissolved in 50 ml of dry methylene chloride and to the solution was added 740 mg (3.87 mmol) of p-toluenesulfonic acid monohydride. The mixture was stirred at room temperature for 1 hour. After washing with saturated aqueous sodium bicarbonate and water, the mixture was dried over anhydrous magnesium sulfate. The residue obtained by concentration under reduced pressure was washed with petroleum ether to obtain 13.5 g (89%) of desired lactone VI-2. mp: 155.5-158°C 1 H-NMR:δ(CDCl 3 ) 2.44(3H,d,J=1.2Hz) 3.85(3H,s) 3.89(3H,s) 6.43(1H,s) 6.77-7.04(4H,m) ppm. Preparations 7 - 8 Syntheses of VI-3, 4 Step-1 (Methyl tetrahydro-5-ethyl-4-oxothiophen-3-carboxylate: 21) To a solution of 33.4 g (330 mmol) of diisopropylamine in 300 ml of dry THF cooled at -78°C, 199 ml of 1.66 M n-BuLi in n-hexane (330 mmol) was added dropwise under nitorogen flow. After completion of the addition, the mixture was stirred at 0°C for additional 30 minutes, and then re-cooled to -78°C. To this cooled reaction mixture, a solution of 24.0 g (150 mmol) of methyl tetrahydro-4-oxothiophen-3-carboxylate 20 [O. Hromatka, D. Binder and K. Eichinger, Monatsh. Chem., 104 , 1520 (1973)] in 30 ml of dry THF was added dropwise, and then the mixture was stirred at -30°C for 30 minutes. To this mixture, 23.4 g (150 mmol) of ethyl iodide was added dropwise at the same temperature over 10 minutes. After addition, the mixture was stirred for additional 2 hours at -20°C. The reaction mixture was acidified by addition of ice and 6N hydrochloric acid, and extracted with ethyl acetate. The extract was washed with water and brine, and dried over anhydrous magnesium sulfate. After concentration under reduced pressure, the residue was purified by column chromatography on silica gel (ethyl acetate:n-hexane = 4:1) to obtain 13.6 g (48%) of desired compound 21 as an oil. 1 H-NMR:δ(CDCl 3 ) 1.00(3H,t,J=7.3Hz) 1.63-2.12(2H,m) 3.66-3.70(2H,m) 3.77(3H,s) 4.12-4.22(1H,m) 10.98(1H,s) ppm. Step-2 (Methyl 4-acetoxy-5-ethylthiophen-3-carboxylate: 22) A mixture of compound 21 obtained above (13.6 g, 72.2 mmol), 41 ml of isopropenyl acetate and 50 mg of p-toluenesulfonic acid monohydrate was heated under reflux for 22 hours. Excess isopropenyl acetate and generated acetone were distilled off under reduced pressure, and then the residue was purified by column chromatography on silica gel (ethyl acetate:n-hexane = 4:1) to obtain 17.2 g of an oil. The oil was dissolved in 150 ml of dry methylene chloride, and to the solution 11.7 g (86.6 mmol) of sulfuryl chloride was added at -20°C over 30 minutes. The mixture was stirred for 1 hour at the same temperature, and then allowed to stand at room temperature overnight. The reaction mixture was washed with saturated aqueous sodium bicarbonate and water, dried over anhydrous magnesium sulfate, and evaporated under reduced pressure to obtain 14.7 g (88%) of desired compound 22 as an oil. 1 H-NMR:δ(CDCl 3 ) 1.24(3H,t,J=7.5Hz) 2.35(3H,s) 2.69(2H,q,J=7.5Hz) 3.81(3H,s) 7.89(1H,s) ppm. Step-3 (Methyl 5-ethyl-4-hydroxythiophen-3-carboxylate: 23) To a solution of compound 22 obtained above (14.8 g, 64.9 mmol) in 41 ml of dry methanol was added 250 mg of p-toluenesulfonic acid monohydrate, and the mixture was heated under reflux for 22 hours. After methanol was distilled off under reduced pressure, saturated aqueous sodium bicarbonate was added thereto. The mixture was extracted with ethyl acetate. The extract was washed with water, dried over anhydrous magnesium sulfate, and evaporated under reduced pressure to obtain 10.4 g (86%) of desired compound 23 as an oil. 1 H-NMR:δ(CDCl 3 ) 1.25(3H,t,J=7.5Hz) 2.74(2H,q,J=7.5Hz) 3.90(3H,s) 7.71(1H,s) 8.52(1H,s) ppm Step-4 (Methyl 5-ethyl-4-methoxythiophen-3-carboxylate: 24) To a solution of compound 23 obtained above (10.1 g, 50 mmol) in 100 ml of dry DMF was added 9.71 g (70.3 mmol) of potassium carbonate and 9.97 g (70.2 mmol) of methyl iodide, and the mixture was stirred at 70°C for 2 hours. After cooling, the mixture was poured into dilute hydrochloric acid and ice, and extracted with ethyl acetate. The extract was washed with water and dried over anhydrous magnesium sulfate. The solvent was distilled off under reduced pressure, and the residue was distilled under reduced pressure to obtain 6.36 g (59%) of desired compound 24 as an oil. bp: 86-93°C (3mmHg) 1 H-NMR:δ(CDCl 3 ) 1.26(3H,t,J=7.6Hz) 2.78(2H,q,J=7.6Hz) 3.83(3H,s) 3.86(3H,s) 7.81(1H,s) ppm Step-5 (5-Ethyl-4-methoxythiophen-3-carboxylic acid: 25) To a solution of compound 24 obtained above (6.36 g, 31.8 mmol) in 50 ml of methanol was added 20 ml of 10% aqueous sodium hydroxide, and the mixture was heated under reflux for 35 minutes. After cooling, dilute hydrochloric acid and ice was added, and the resulting mixture was extracted with ethyl acetate. The extract was washed with water and dried over anhydrous magnesium sulfate. The solvent was distilled off under reduced pressure, and the residue was purified by column chromatography on silica gel (methylene chloride:methanol = 19:1) to obtain 4.74 g (80%) of desired compound 25. mp: 109-112°C 1 H-NMR:δ(CDCl 3 ) 1.29(3H,t,J=7.5Hz) 2.72(2H,q,J=7.5Hz) 3.89(3H,s) 7.99(1H,s) ppm Step-6 The reaction was conducted similarly to that of Step-2 in Preparation 6 to obtain VI-3 and VI-4 from 4-methoxy-3-thiophenecarboxylic acid [J. B. Press, C. M. Hofmann and S. R. Safir, J. Org. Chem., 44 , 3292 (1979)] and 5-ethyl-4-methoxythiophen-3-carboxylic acid 25, respectively. Yields and physical properties are shown below. Preparation 7 (VI-3); Yield: 45% (through 2 steps) mp: 158.5-160.5°C (ether) 1 H-NMR:δ(CDCl 3 ) 2.85(3H,s) 3.89(3H,s) 3.94(3H,s) 6.34(2H,s) 6.76-6.96(3H,m) ppm. Preparation 8 (VI-4); Yield: 86% (through 2 steps) 1 H-NMR:δ(CDCl 3 ) 1.24(3H,t,J=7.5Hz) 2.68-2.83(2H,m) 3.86(3H,s) 3.89 (3H,s) 4.13(3H,s) 6.30(1H,s) 6.78-6.94(3H,m) ppm. Preparations of compound (VII) are shown below. Preparation 9 Synthesis of methyl (E)-5-ethyl-4-oxo-2-heptenoate: VII-2 Step-1 ((2-Ethylbutyliden)azanol: 27) A solution of 40.0 g (400 mmol) of (2-ethyl)butyraldehyde in 250 ml of 99% ethanol was added dropwise to a solution of 30.6 g (440 mmol) of hydroxylamine hydrochloride and 33.1 g (240 mmol) of potassium carbonate under cooling in an ice-bath. After the addition, the mixture was allowed to warm to room temperature while being stirred for 1.5 hours, and then the resulting mixture was diluted with 500 ml of ice water and extracted with ether. The extract was washed with water and brine, dried over anhydrous magnesium sulfate, and concentrated under reduced pressure to obtain 48.1 g of desired compound 27 as a crude oily product, which was used in the next reaction without purification. Step-2 (3-(1-Ethyl)propyl-5-(methoxycarbonyl)-2-isooxazoline: 28) To a mixture of 400 ml of about 10% aqueous sodium hypochlorite (about 600 mmol) and a solution of 40.0 ml (440 mmol) of methyl acrylate and 5.57 ml (40 mmol) of triethylamine in 150 ml of methylen chloride, a solution of 48.1 g of crude oxime 27 obtained above in 150 ml of methylene chloride was added dropwise with vigorous stirring under cooling in an ice-bath. After the addition, the mixture was allowed to warm to room temperature with stirring for 2 hours. Ice and water were added, and then the mixture was extracted with methylene chloride. The extract was dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residue was distilled under reduced pressure to obtain 60.2 g (75.7%, through 2 steps) of desired compound 28 as an oil. bp: 95-97°C (1mmHg) 1 H-NMR:δ(CDCl 3 ) 0.88(3H,t,J=7.4Hz) 0.89(3H,t,J=7.4Hz) 1.33-1.71(4H,m) 2.36-2.53(1H,m) 3.13(1H,d,J=9.6Hz) 3.14(1H,d,J=7.8Hz) 3.79(3H,s) 4.99(1H,dd,J=9.6Hz,7.8Hz) ppm. Step-3 (Methyl 5-ethyl-2-hydroxy-4-oxoheptanoate: 29) Isooxazoline 28 obtained above (45.4 g, 228 mmol) was dissolved in a solvent mixture of 200 ml of methanol, 40 ml of water and 40 ml of acetic acid, and the mixture was stirred at room temperture for 5 hours in the presence of 1.36 g of 10% Pd-C under hydrogen atomosphere. After filtering off Pd-C, the mixture was diluted with 200 ml of water, and extracted with ether. The extract was washed with water, saturated aqueous sodium bicarbonate, and brine, dried over anhydrous magnesium sulfate, and concentrated under reduced pressure to obtain 42.3 g of desired compound 29 as a crude oily product, which was subjected to the next reaction without purification. Step-4 (VII-2) To a solution of 42.3 g of crude hydroxyketone 29 obtained above and 139 ml (838 mmol) of triethylamine in 200 ml of dry benzene was added 24.3 ml of methanesulfonyl chloride under cooling in an ice-bath, and the mixture was allowed to warm to room temperature while being stirred overnight. The reaction mixture was diluted with 300 ml of water and extracted with ethyl acetate. The extract was washed with water, 2N HCl, water and brine, successively. The mixture was dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residue was distilled under reduced pressure to obtain 32.1 g (76.5%, through 2 steps) of desired compound VII-2 as an oil. bp: 64-67°C (0.5mmHg) 1 H-NMR:δ(CDCl 3 ) 0.86(6H,t,J=7.4Hz) 1.42-1.80(4H,m) 2.51-2.70(1H,m) 3.82(3H,s) 6.72(1H,d,J=15.8Hz) 7.19(1H,d,J=15.8Hz) ppm. Preparations 10 - 11 VII-1 and VII-3 The reactions were conducted similarly to that of Preparation 9 to obtain compound VII-1 and 3. The physical properties are shown below. Preparation 10 (VII-1) ; bp: 87-90°C (8mmHg) 1 H-NMR:δ(CDCl 3 ) 1.14(3H,t,J=7.2Hz) 2.67(2H,q,J=7.2Hz) 3.81(3H,s) 6.69(1H,d,J=16.0Hz) 7.09(1H,d,J=16.0Hz) ppm. Preparation 11 (VII-3) ; bp: 75-76°C (0.8mmHg) 1 H-NMR:δ(CDCl 3 ) 0.86(6H,t,J=7.2Hz) 1.19-1.50(4H,m) 1.79-1.96(1H,m)2.54(2H,d,J=6.6Hz) 3.82(3H,s) 6.67(1H,d,J=15.8Hz) 7.09(1H,d,J=15.8Hz)ppm. Example 1 Synthesis of compound I-1 1-(3,4-dimethoxyphenyl)-3-(3-ethyl-1-oxopentyl)-4-hydroxy-2-methoxycarbonyl-6,7,8-trimethoxy-naphthalene: Step-1 (1,2-Dihydro-1,4-dihydroxy-1-(3,4-dimethoxyphenyl)-3-(3-ethyl-1-oxopentyl)-2-(methoxycarbonyl)-6,7,8-trimethoxynaphthalene; VIII-1) Under nitrogen flow, 30 ml of 1.68 M n-BuLi in n-hexane (50.4 mmol) was added dropwise to a solution of 10.6 ml (50.4 mmol) of (TMS) 2 NH in 35 ml of dry THF under cooling in an ice-bath. After addition, the mixture was stirred at the same temperature for 20 minutes and then cooled to -78°C. To the cooled solution, a solution of lactone VI-1 obtained in Preparation 16 (9.00 g, 25.0 mmol) in 25 ml of dry methylene chloride was added dropwise over 20 minutes. After stirring for 25 minutes, a solution of unsaturated ketoester VII-3 obtained in Preparation 26 (5.45 g, 27.5 mmol) in 20 ml of dry THF was added dropwise over 20 minutes. After the addition, 8.8 ml (27.5 mmol) of HMPA was added thereto and the mixture was warmed to 0°C. The reaction mixture was stirred under cooling in an ice-bath for 2.5 hours. Ice and 50 ml of 2N HCl were added to the reaction mixture, and the resulting mixture was extracted with ethyl acetate. The extract was washed with water and brine, and dried over anhydrous magnesium sulfate. After concentration under reduced pressure, the residue was crystallized from 35 ml of methanol, and then recrystallized twice from 30 ml of methanol to obtain 8.93 g (63.9%) of desired compound VIII-1. mp: 132-133°C 1 H-NMR:δ(CDCl 3 ) 0.65(3H,t,J=7.2Hz) 0.69(3H,t,J=7.2Hz) 0.80-1.29(5H,m) 2.03(1H,dd,J=14.0Hz,7.0Hz) 2.31(1H,dd,J=14.0Hz,6.4Hz) 3.40(3H,s) 3.67(3H,s) 3.81(3H,s) 3.86(3H,s) 3.88(1H,s) 3.94(3H,s) 3.99(3H,s) 5.73(1H,s) 6.43(1H,dd,J=8.4Hz,2.2Hz) 6.64(1H,d,J=8.4Hz) 7.14(1H,d,J=2.2Hz) 7.54(1H,s) ppm. Step-2 (I-1) Under nitrogen atmosphere, a solution of BF 3 ·OEt 2 (2.56 ml, 208 mmol) in 7 ml of dry methylene chloride was added dropwise under cooling in an ice-bath to a solution of compound VIII-1 obtained above (8.93 g, 160 mmol) in 40 ml of dry methylene chloride over 10 minutes, and the mixture was stirred at the same temperature for 17 minutes. To the reaction mixture was added 4.0 ml (28.8 mmol) of triethylamine, and the resulting mixture was stirred at room temperature for 10 minutes. Water was added to the reaction mixture, which was then extracted with methylene chloride. The extract was washed with 1N hydrochloric acid, water and brine, and dried over anhydrous magnesium sulfate. The mixture was concentrated under reduced pressure and the residue was crystallized from 30 ml of methanol. Further recrystallization from 30 ml of methanol gave 8.32 g (96.3%) of desired compound I-1. mp: 127.5-128.5°C Example 1 Synthesis of compound I-4 1-(3,4-Dimethoxyphenyl)-3-(2-ethyl-1-oxobutyl)-4-hydroxy-2-methoxycarbonyl-6,7,8-trimethoxynaphthalene: Step-1 (1,2-Dihydro-1,4-dihydroxy-1-(3,4-dimethoxyphenyl)-3-(2-ethyl-1-oxobutyl)-2-(methoxycarbonyl)-6,7,8-trimethoxynaphthalene: VIII-4) Under nitrogen flow, 59.6 ml of 1.68 M n-BuLi in n-hexane (50.0 mmol, 2.0 eq) was added dropwise to a solution of 21.2 ml of (TMS) 2 NH (50.0 mmol, 2.0 eq) in 10 ml of dry THF under cooling in an ice-bath. After the addition, the mixture was stirred at the same temperature for 20 minutes and then cooled to -78°C. To the cooled solution, a solution of lactone VI-1 obtained in Preparation 1 (18.0 g, 50.0 mmol) in 80 ml of dry DMF was added dropwise over 30 minutes. After stirring for 20 minutes, a solution of unsaturated ketoester VII-2 obtained in Preparation 9 (11.0 g, 60.0 mmol) in 40 ml of dry THF was added dropwise thereto over 12 minutes. After stirring at the same temperature for 25 minutes, the mixture was warmed to 0°C over 35 minutes. The reaction mixture was stirred under cooling in an ice-bath for 3.5 hours. Ice and 100 ml of 2N HCl was added to the reaction mixture, and the resulting mixture was extracted with ethyl acetate. The extract was washed with water and brine, and dried over anhydrous magnesium sulfate. After concentration under reduced pressure, the residue was crystallized from 100 ml of methanol, and then recrystallized from 100 ml of methanol to obtain 15.1 g (55.4%) of desired compound VIII-4. mp: 156-157°C 1 H-NMR:δ(CDCl 3 ) 0.19(3H,t,J=7.4Hz) 0.75(3H,t,J=7.4Hz) 1.13-1.72(4H,m) 2.35-2.51(1H,m) 3.42(3H,s) 3.65 (3H,s) 3.79(3H,s) 3.86(3H,s) 3.94(3H,s) 3.96(1H,s) 3.99(3H,s) 5.76(1H,s) 6.42(1H,dd,J=8.4Hz,2.2Hz) 6.64(1H,d,J=8.4Hz) 7.14(1H,d,J=2.2Hz) 7.56(1H,s) ppm. Step-2 (Compound I-4) Under nitrogen atmosphere, a solution of 4.43 ml of BF 3 ·OEt 2 (36.0 mmol, 1.3 eq) in 20 ml of dry methylene chloride was added dropwise under cooling in an ice-bath to a solution of compound VIII-4 obtained above (15.1 g, 27.7 mmol) in 150 ml of dry methylene chloride over 7 minutes, and the mixture was stirred at the same temperature for 10 minutes. To the reaction mixture was added 9.64 ml (69.3 mmol, 2.5 eq) of triethylamine, and the resulting mixture was stirred at room temperature for 5 minutes. Water was added to the reaction mixture, which was then extracted with ethyl acetate. The extract was washed with 1N hydrochloric acid, water and brine, and dried over anhydrous magnesium sulfate. The mixture was concentrated under reduced pressure and the residue was crystallized from 60 ml of 90% aqueous ethanol, and then recrystallized from 50 ml of 80% aqueous ethanol to obtain 11.3 g (77.3%) of desired compound I-4. mp: 113-114°C 1 H-NMR:δ(CDCl 3 ) 0.82(3H,t,J=8Hz) 0.83(3H,t,J=8Hz) 1.42-1.60(2H,m) 1.64-1.81(2H,m) 2.78-2.90(1H,m) 3.24(3H,s) 3.42(3H,s) 3.86(3H,s) 3.89(3H,s) 3.93(3H,s) 4.03(3H,s) 6.81-6.87(3H,m) 7.72(1H,s) 14.18(1H,s) ppm. Examples 3 to 12 According to the method in Example 1, the compounds of Examples listed below were synthesized. Example 3 7-(3,4-Dimethoxyphenyl)-4-hydroxy-6-methoxycarbonyl-3-methyl-5-(1-oxopropyl)benzo[b]thiophene Using compound VI-2 (Preparation 6) and compound VII-1 (Preparation 10), the title compound was obtained. Example 4 7-(3,4-Dimethoxyphenyl)-5-(3-ethyl-1-oxopentyl)-4-hydroxy-6-methoxycarbonyl-3-methylbenzo[b]thiophene Using compound VI-2 (Preparation 6) and compound VII-3 (Preparation 11), the title compound was obtained. The structures and the physical properties of the compounds listed above are shown in Table 1 and Table 3 hereinafter, respectively. Example 5 7-(3,4-Dimethoxyphenyl)-4-hydroxy-3-methoxy-6-methoxy-carbonyl-5-(1-oxopropyl)benzo[b]thiophene Using compound VI-3 (Preparation 7) and compound VII-1 (Preparation 10), the title compound was obtained. Example 6 7-(3,4-Dimethoxyphenyl)-5-(3-ethyl-1-oxopentyl)-4-hydroxy-3-methoxy-6-(methoxycarbonyl)benzo[b]thiophene Using compound VI-3 (Preparation 7) and compound VII-3 (Preparation 11), the title compound was obtained. Example 7 7-(3,4-Dimethoxyphenyl)-2-ethyl-4-hydroxy-3-methoxy-6-methoxycarbonyl-5-(1-oxopropyl)benzo[b]thiophene Using compound VI-4 (Preparation 8) and compound VII-1 (Preparation 10), the title compound was obtained. Example 8 7-(3,4-Dimethoxyphenyl)-2-ethyl-5-(3-ethyl-1-oxopentyl)-4-hydroxy-3-methoxy-6-(methoxycarbonyl)benzo[b]thiophene Using compound VI-4 (Preparation 8) and compound VII-3 (Preparation 11), the title compound was obtained. The structures and the physical properties of the compounds listed above are shown in Table 1 and Table 4 hereinafter, respectively. Example 9 1-(3,4-Difluorophenyl)-3-(3-ethyl-1-oxopentyl)-4-hydroxy-2-methoxycarbonyl-6,7,8-trimethoxynaphthalene Using compound VI-5 (Preparation 2) and compound VII-3 (Preparation 11), the title compound was obtained. Example 10 1-(3,4-Dichlorophenyl)-3-(3-ethyl-1-oxopentyl)-4-hydroxy-2-methoxycarbonyl-6,7,8-trimethoxynaphthalene Using compound VI-6 (Preparation 3) and compound VII-3 (Preparation 11), the title compound was obtained. Example 11 1-[3,4-(Ethylenedioxy)phenyl]-3-(3-ethyl-1-oxopentyl)-4-hydroxy-2-methoxycarbonyl-6,7,8-trimethoxynaphthalene Using compound VI-7 (Preparation 4) and compound VII-3 (Preparation 11), the title compound was obtained. Example 12 3-(3-Ethyl-1-oxopentyl)-1-(3-fluoro-4-methoxyphenyl)-4-hydroxy-2-methoxycarbonyl-6,7,8-trimethoxynaphthalene Using compound VI-8 (Preparation 5) and compound VII-3 (Preparation 11), the title compound was obtained. The structures and the physical properties of the compounds listed above are shown in Table 2 and Table 5 hereinafter, respectively.

Claims: A process for preparing a compound represented by the formula (I): wherein R 1 is a C 1 -C 6 alkyl, cycloalkyl, cycloalkyl-C 1 -C 6 alkyl, aryl or aralkyl group which is optionally substituted. R 2 is a group represented by the formula: -COOR' (wherein R' is a C 1 -C 6 alkyl or aralkyl which is optionally substituted), C 1 -C 6 alkyl, or halogenated C 1 -C 6 alkyl, or, R 1 and R 2 , together with adjacent carbonyl group, form a cyclohexanone ring represented by the formula: R 3 is a phenyl group optionally being substituted, and, ring A is a benzene nucleus which is optionally substituted, or a heterocyclic ring containing S or O optionally being substituted, which process is characterized by that a lactone compound represented by the formula (VI): in which R 3 and ring A are as defined above, is allowed to react with a compound of a formula (VII): in which R 1 and R 2 are as defined above in the presence of a base, and then the resulting compound is subject to dehydration in the presence of an acid. A process as claimed in claim 1 wherein the compound is represented by the formula (I'): in which R 1 is ethyl, 1-ethylpropyl, or 2-ethylbutyl; R 12 , R 13 and R 14 are methoxy; R 15 and R 16 are methyl; and R 17 is methyl; which process is characterized in that a lactone compound represented by the formula (VI'); in which R 12 , R 13 , R 14 , R 15 , and R 16 are defined above, is allowed to react with a compound of a formula (VII'); in which R 1 and R 17 are as defined above in the presence of a base, and then the resulting compound is subjected to dehydration in the presence of an acid. A compound of the formula (VI'); in which R 12 , R 13 and R 14 are methoxy; and R 15 and R 16 are methyl. A compound of the formula (VII'); in which R 1 is ethyl, 1-ethylpropyl or 2-ethylbutyl; and R 17 is methyl.

Inventors: ICHIHASHI TERUHISA, KIDA SHIRO, MIZUI TAKUJI, MORI SACHIO, TAKECHI SHOZO, ICHIHASHI, TERUHISA, KIDA, SHIRO, MIZUI, TAKUJI, MORI, SACHIO, TAKECHI, SHOZO
Applicants: SHIONOGI & CO, SHIONOGI & CO., LTD.
Application year: 1992
Main classification: C07C69
IPC codes: C07C69, C07D319, C07D307, C07D317