Absorption spectra of ketones. Part X. Photochemical rearrangement of bicyclo[2,2,1]hepten-2-ones to bicyclo[3,2,0]hept-2-en-7-ones and their ultraviolet and circular-dichroic spectra

Abstract

Irradiation at the wavelength of the intense n→π* transition of the bornenones (IV to VII) interconverts them with the isomeric bicyclo[3,2,0]hept-2-en-7-ones by migration of the carbonyl group from one end to the other of the allyl system. Longer irradiation causes dissociation into keten and the appropriate trimethylcyclopentadiene, as with the parent system.

The photoketones are optically active, showing similar intensified ultraviolet absorption and circular dichroism of the n→π* transition to those of the precursors. The complementary π→π* transitions are again of opposite sign in the circular dichroism.