1,2-Dimethoxyethane → Ramosetron hydrochloride

Participants

Reaction Conditions

Reaction Steps

By heating a mixture of 4.05 g of (R)-4,5,6,7-tetrahydro-1H-benzimidazole-5-carboxylic acid monohydrochloride (99.4% e.e.), 120 ml of dimethoxyethane and 5.47 g of thionyl chloride at 70° C. for 2 hours, (R)-4,5,6,7-tetrahydro-1H-benzimidazole-5-carbonyl chloride was synthesized, and the solvent was evaporated under a reduced pressure. A 80 ml portion of toluene was added to the residue and again evaporated under a reduced pressure, and the residue was mixed with 120 ml of toluene and 5.24 g of 1-methyl-1H-indole and cooled to −25° C. in an atmosphere of nitrogen. A 33 ml portion of 1.8 mol/l toluene solution of diethylaluminum chloride was slowly added to this liquid and stirred at −25° C. for 2 hours, and 8 ml of tetrahydrofuran was added thereto after the stirring. This liquid was slowly dispersed in 100 ml of water which was cooled at 0° C., and then heated to 45° C. After removing the organic layer, the water layer was washed with 40 ml of toluene, and this was extracted by adding 80 ml of 2-butanone and 50 ml of 20% sodium hydroxide aqueous solution thereto. The water layer was washed with 40 ml of 2-butanone, and the organic layers were combined and washed twice with 20 ml of 10% brine and then with 4 ml of water. The thus obtained organic layer was evaporated under a reduced pressure, 40 ml of ethanol was added to the resulting residue and evaporated under a reduced pressure, and 40 ml of ethanol was again added to the residue and evaporated under a reduced pressure. A 120 ml portion of a mixed solvent of ethanol and ethyl acetate (1:3) was added to the residue, and this was heated at 70° C. for 12 hours by adding 5 ml ethyl acetate solution of 4 mol/l hydrogen chloride and then slowly cooled to 0° C. The precipitated crystals were filtered, and the crystals were washed with an ethanol-ethyl acetate mixed solvent and then dried in vacuo at 50° C., thereby obtaining 5.45 g of (−)-(R)-5-[(1-methyl-1H-indol-3-yl)carbonyl]-4,5,6,7-tetrahydro-1H-benzimidazole monohydrochloride (yield 86.3%, 99.2% e.e.). FAB-MS (m/z): 280 [M+H+]

Provenance & Evidence