Photo-[4+4]-cycloaddition of enynes

ORGN 643

Svitlana Kulyk and Scott McN. Sieburth, Department of Chemistry, Temple University, 1901 N. 13th Street, Philadelphia, PA 19122
1,3-Enynes are well known as 'dienes' in high temperature Diels-Alder reactions, wherein the 1,2,4-cyclohexatriene intermediate isomerizes to benzene derivatives (see Danheiser, et al., J. Org. Chem. 1994, 59, 5514.). We are studying the analogous [4+4] photocycloaddition of enynes with 1,3-dienes to give 1,2,5-cyclooctatrienes, with 2-pyridones as the 1,3-diene component. Pyridones are promiscuous 4+4 cycloaddition partners, photochemically combining with 1,3-dienes, furan, naphthalene and other 2-pyridones. The cyclooctatriene product can be formed as four regio- and diastereomeric isomers. Isolated products are consistent with the intermediacy of these highly strained bicyclic allenes.