Triggering of the Bergman cyclization by photochemical ring contraction. Facile cycloaromatization of benzannulated cyclodeca-3,7-diene-1,5-diynes

Abstract

Eleven-membered ring enediyne 1, which incorporates α-diazo-β-diketone moiety, undergoes efficient light-induced ring contraction to produce two isomeric ten-membered ring enediyne compounds. The latter undergo spontaneous facile Bergman cyclization at or below room temperature. In the photochemical or thermal Wolff rearrangement of 1 the alkyl substituent migrates ca. 2 times faster than the alkynyl group.