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

Abstract The 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 ).