Acetic Anhydride → 6-(5-chloro-2-pyridyl)-5H-pyrrolo[3,4-b]pyrazine-5,7(6H)-dione

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In Indian Published Patent Application No. 645/MUM/2004 discloses the reaction of pyrazine-2,3-dicarboxylic acid with acetic anhydride and concomitant reaction with 2-amino-5-chloro pyridine at a temperature of 120-130° C. in a mole ratio 1.23:1 to obtain 6-(5-chloropyrid-2-yl)-5,7-dioxo-5,6-dihydropyrrolo[3,4-b]pyrazine, which is selectively reduced with sodium borohydride in the presence of organic solvent-water system. The product, 6-(5-chloropyrid-2-yl)-5-hydroxy-7-oxo-5,6-dihydropyrrolo[3,4-b]pyrazine (V) is reacted with 1-chlorocarbonyl-4-methyl piperazine in pyridine and methylene chloride system to yield 6-(5-chloro-2-pyridinyl)-6,7-dihydro-7-oxo-5H-pyrrolo-[3,4-b]pyrazin-5-yl-4-methyl piperazine-1-carboxylate (zopiclone).

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