Photochemistry of two diphenyl β,γ‐enones and a series of methyl‐ and phenyl‐substituted α‐phenyl ketones

Abstract

AbstractThe photochemistry of the diphenyl β,γ‐enones 2 and 3 and the methyl‐ and phenyl‐substituted α‐phenyl ketones 4‐9 has been studied, using mainly benzene as solvent. Irradiation of 2 with λ 300 nm leads to the 1,3‐acyl shift (1,3‐AS) product 17, relatively small amounts of the decarbonylation products 15 and 16, and the photo‐oxidation products benzophenone (18) and the α,β‐unsaturated aldehyde 19. Direct irradiation of the 1,3‐AS product 17 yields 15, 16, 18 and 19, but no 2.Direct irradiation of 3 with λ 350 nm leads mainly to the formation of 1,3‐AS products (E)‐ and (Z)‐22, the decarbonylation products (E)‐ and (Z)‐20 and 21 and, in addition, a small amount of the cis‐di‐π‐methane isomer 23.Direct irradiation of the substituted α‐phenyl ketones 4, 5, 8 and 9 with γ 300 nm leads predominantly to the formation of the radical coupling products 2,3‐butanedione and 24‐27, respectively, whereas 6 and 7 yield 1,2‐diphenyl‐1,2‐ethanedione and the respective 24 and 25. The acetone‐sensitized irradiation of 4 leads to 4‐phenyl‐2‐butanone (33) in addition to 2,3‐butanedione and 1,2‐diphenylethane (24).