Cyanoethylations and Michael additions. VIII. The use of preformed enolate ions in Michael additions. Part I

Abstract

Some Michael additions involving preformed enolate ions as nucleophiles were studied. High regioselectivity was observed in the additions of the lithium enolate of 2-methylcyclo-hexanone to ethyl acrylate and to methyl β-chloroacrylates, the latter reactions being by far superior to those involving classical Michael additions. The addition to cis- and trans-β-chloroacrylates proceeded with appreciable stereoselectivity. Michael addition of a preformed enolate ion, derived from a ketone, to a cis-β-chloroacrylate constitutes an efficient pathway to 6-substituted α-pyrones, as exemplified by the synthesis of 5,6,7,8-tetrahydrocoumarin from cyclohexanone.