Patent ID: 7125874

Claim:
A method of making a dextrorotatory isomer of zopiclone, 6-(5-chloro-2-pyridyl)-5-[4-methyl-1-piperazinyl) carbonyloxy]-7-oxy-6,7-dihydro-5H-pyrrolo[3,4-b]pyrazine, comprising the steps of: a) forming a first reaction mixture by mixing a solution of an optically active acid in dichloromethane to a solution of zopiclone in dichloromethane; b) concentrating the reaction mixture to dryness under reduced pressure to form a dry salt; c) recrystallizing the salt in acetonitrile to form a first crystallized product; d) dissolving the crystallized product in dichloromethane with reflux; e) adding acetonitrile to form a second reaction mixture; f) maintaining the second reaction mixture to form a second crystallized product and recrystallizing the second crystallized product to obtain a crystallized salt; g) dissolving the crystallized salt in water in the presence of dichloromethane to form a third reaction mixture; h) alkalinizing the third reaction mixture to pH 11, collecting a first organic phase, extracting a remaining aqueous phase at least once with dichloromethane to obtain a second organic phase, collecting the second organic phase, and recombining the first and second organic phases; i) washing the recombined organic phases in water, then drying over magnesium sulfate, then filtering; j) evaporating the solvent and recrystallizing the resulting product in acetonitrile to obtain the dextrorotatory zopiclone isomer.