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)cyclohexan one was studied in solution and in crystals to determine its photoreactivity and chemoselectivity. Although 1,3-acyl shifts and the oxadi-pi-methane rearrangement products are possible for the beta,gamma-unsaturated chromophore, an efficient intramolecular abstraction of an allylic gamma-hydrogen and small amounts of alpha-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. (C) 2003 Elsevier Ltd. All rights reserved.