Patent ID: 7786304

Claim:
A process for preparing (S)-6-(5-chloro-2-pyridinyl)-6,7-dihydro-7-oxo-5H-pyrrolo-[3,4-b]pyrazin-5-yl-4-methyl piperazine-1-carboxylate (eszopiclone), comprising the steps of: a) reacting, in a single pot, 2-amino 5-chloropyridine with pyrazine-2,3-dicarboxylic acid anhydride in a molar ratio of 1.05:1, in a first inert organic solvent, at room temperature to obtain 3-(5-chloropyrid-2-yl)carbamoyl-2-pyrazine-2-carboxylic acid; b) cyclizing, in a single pot, the 3-(5-chloropyrid-2-yl)carbamoyl-2-pyrazine-2-carboxylic acid in a second inert organic solvent in presence of triethyl amine and ethylchloroformate to obtain 6-(5 chloropyrid-2-yl)-5,7-dioxo-5,6-dihydropyrrolo[3,4-b]pyrazine; c) reducing the 6-(5-chloropyrid-2-yl)-5,7-dioxo-5,6-dihydropyrrolo[3,4-b]pyrazine to obtain 6-(5-chloropyrid-2-yl)-5-hydroxy-7-oxo-5,6-dihydropyrrolo[3,4-b]pyrazine; d) reacting 6-(5-chloropyrid-2-yl)-5-hydroxy-7-oxo-5,6-dihydropyrrolo[3,4-b]pyrazine with 1-chlorocarbonyl-4-methylpiperazine hydrochloride in a third organic solvent in a presence of triethyl amine along with a catalytic amount of an acylation catalyst to obtain racemic zopiclone; e) recrystallizing the zopiclone from an alkyl ester solvent followed by purifying in suitable alcohols; and f) resolving the racemic zopiclone by treatment with (+)-O—O′-dibenzoyltartaric acid to obtain eszopiclone.