The photochemistry of a two-carbon ortho-ortho phenyl-bridged 4,4-diphenyl-2-cyclohexen-1-one

Abstract

The synthesis and photochemistry of 10′,11′-dihydrospiro[2-cyclohexene-1,5′-[5H]-dibenzo[ a,d]cyclohepten]-4-one ( 9) are described. The irradiation of 9 resulted in the formation of four photoproducts, three resulting from aryl migration and the fourth deriving from an incomplete type A mechanism. These were identified as the six-ring α,β-enone system 10, the cis- and trans-diphenyl tricyclic systems 11 and 12 and the five-ring β,γ-enone 13. A significant solvent effect on product ratios was observed on irradiation of 9 in tert-butyl alcohol, benzene and cyclohexane. While the α,β-enone 10 was kinetically preferred in tert-butyl alcohol, irradiation in benzene and cyclohexane led preferentially to the trans-diphenyl product 12. The α,β-enone was the photodynamic product in all solvents. Control irradiations suggested that all four photoproducts result from both primary and secondary photoreactions. Mechanisms for both the primary and secondary reactions are discussed. Finally, comparisons are made with the photochemistry of the zero- and three-carbon bridged analogs 4a and 4b, as well as the parent system 4,4-diphenyl-2-cyclohexen-1-one ( 1).