Zopiclone → 3-(5-Chloropyrid-2-yl)carbamoylpyrazine-2-carboxylic acid

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U.S. Pat. No. 3,862,149 describes a process for preparing zopiclone. The process comprises reacting 2-amino-5-chloropyridine with pyrazine 2,3-dicarboxylic acid anhydride to obtain 3-(5-chloropyrid-2-yl)carbamoyl-pyrazine-2-carboxylic acid, which is further treated with thionyl chloride to obtain 6-(5-chloropyrid-2-yl)-5,7-dioxo-5,6-dihydro-5H-pyrrolo[3,4-b]pyrazine 6-(5-chloropyrid-2-yl)-5,7-dioxo-5,6-dihydro-5H-pyrrolo[3,4-b]pyrazine is reduced using potassium borohydride in a mixture of dioxane and water followed by neutralization with acetic acid to obtain 6-(5-chloropyrid-2-yl)-5-hydroxy-7-oxo-5,6-dihydro-5H-pyrrolo[3,4-b]-pyra-zine. The reaction of 6-(5-chloropyrid-2-yl)-5-hydroxy-7-oxo-5,6-dihydro-5H-pyrrolo[3,4-b]pyra-zine with 1-chlorocarbonyl-4-methyl piperazine in anhydrous dimethyl formamide and sodium hydride (50% dispersion in mineral oil) yields the final product, Zopiclone.

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