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 −40° C. in an atmosphere of nitrogen. A 30 ml portion of 1.0 mol/l toluene solution of ethylaluminum sesquichloride was slowly added to this liquid and stirred at −40° C. for 3 hours, and 10 ml of tetrahydrofuran was added thereto after the stirring. This liquid was slowly dispersed in 160 ml of water cooled at 0° C., and after removing the organic layer, the water layer was washed with 40 ml of toluene and 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. A 40 ml portion of ethanol was added to the thus obtained organic layer 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 1 hour 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 4.98 g of (−)-(R)-5-[(1-methyl-1H-indol-3-yl)carbonyl]-4,5,6,7-tetrahydro-1H-benzimidazole monohydrochloride (yield 78.8%, 99.5% e.e.). FAB-MS (m/z): 280 [M+H+]

Provenance & Evidence