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■ Photochemistry of Bridged Stilbene Oxides

Kazuyoshi Nishiyama, Kiyoyasu Ishikawa, Ila Sarkar, David C. Lankin, and Gary W. Griffin*

*Department of Chemistry, University of New Orleans, New Orleans, LA 70148, U.S.A.

Abstract

The photochemistry of a pair of stilbene oxides in which the 2,3-positions are bridged by three and four methylene groups has been studied and compared with a lower homolog. Evidence is provided that cyclic ylides are produced upon photolysis of these oxiranes in solution at 254 nm. The primary photoproducts derived from the ylides in turn are β-styrylpropio- and β-styrylbutyrophenones, respectively. In the latter case Norrish type I1 cleavage then occurs to give as final products, 1-phenylbutadiene and acetophenone. The bridged oxiranes were shown to be more photostable than their open chain analogs and on the basis of double irradiation experiments it was established that a carbene rather than a conventional diradical process is operative or competes in the ylide photocleavage and ketone formation.