H-abstraction prevails over α-cleavage in the solution and solid state photochemistry of cis-2,6-di(1-cyclohexenyl)cyclohexanone

The photochemistry of cis-2,6-di(1-cyclohexenyl)cyclohexanone was studied in solution and in crystals to determine its photoreactivity and chemoselectivity. Although 1,3-acyl shifts and the oxadi-π-methane rearrangement products are possible for the β,γ-unsaturated chromophore, an efficient intramolecular abstraction of an allylic γ-hydrogen and small amounts of α-cleavage and decarbonylation were observed. The mechanism of the Norrish type-II reaction and the selectivity of product formation were analyzed in terms of structural information obtained by X-ray diffraction analysis.