Photolysis of 2,3-epoxy-7,7-diphenylbicyclo[3.2.0]heptan-6-ones and 2-exo, 3-exo-dihydroxy-7,7-diphenylbicyclo[3.2.0]heptan-6-one

Abstract

Photolysis of 2,3-endo-epoxy-7,7-diphenylbicyclo [3.2.0] heptan-6-one (2) in methanol gave products (4), (8) derived from an oxacarbene intermediate and the products (5)–(7), (9) derived from an initially formed alkenylketene. Photolysis of the same epoxide in benzene containing methanol (0.2M) gave the oxo-ester (10) as a major product whilst photolysis of (2) in benzene alone gave the lactone (11). The isomeric epoxide (3) behaved in a similar fashion giving the oxo-ester (10) on photolysis in benzene–methanol and the lactone (11) on photolysis in benzene alone. The homologous epoxide (13) gave products (14), (15) resulting from photon-induced ring-expansion. The dihydroxy ketone (16) gave the hydroxy lactone (17) in 66% yield by intramolecular trapping of the intermediate ketene.