Eleven-membered ring enediyne 1, which incorporates an alpha-diazo-beta-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.