Lewis acid- or base-catalysed double ring closure of diacetylenic compounds with activated olefins

Abstract

Conformationally rigid 1,6- or 1,7-dialkynes, terminally substituted with one or two alkyl groups, react with activated olefins in the presence of Lewis acids or bases to give a double ring closure to alkylidenecyclohexene compounds. The new reaction involves isomerization of the dialkyne to a cyclic ene-allene, which in its turn reacts with activated olefins regioselectively to give condensed rings.