Acylation of enamines with phosgene and the synthesis of heterocycles

Abstract

Enamine acylation with phosgene yields a chlorocarbonyliminium salt or an enamino-acyl chloride depending on whether the enamine does or does not bear a β-hydrogen atom. The reaction, which occurs under milder conditions than methoxycarbonylation with methyl chloroformate, provides reactive intermediates for the synthesis of β-keto-acid derivatives and heterocyclic compounds. In particular, enamino-esters have been obtained by methanolysis of enamino-acyl chlorides and used in the preparation of several new polycyclic pyrimidones derived structurally from pyrido[1,2-a]pyrimidin-4-one. The configurations of two enamino-esters and their corresponding amides are discussed.