Synthesis of Cycloalkanone‐Substituted Ketene Aminals and their Reaction with Ethyl Propiolate

Abstract
2‐[Bis(methylthio)methylene]cycloalkanones 1 react with diamines to give the corresponding 2‐[tetrahydropyrimidin‐2(1H)‐ylidene]cycloalkanones 2a–e and 2‐(2‐imidazolidinylidene)cycloalkanones 2f, g. The ketene aminals 2 react with ethyl propiolate in alcoholic solution to afford 9‐[(alkoxycarbonyl)‐alkyl]pyrido[1,2‐a]pyridines 5a–e, 6c, e, and 8‐[(alkoxycarbonyl)alkyl]imidazo[1,2‐a]pyridines 5f, g 6g via ring cleavage of the cyclic ketones. This facile ring cleavage of cyclic ketones is unusual.

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