Photochemical behaviour of biased homo-conjugated ketones: details of an oxa-di-π-methane rearrangement

Abstract

The acetone sensitized irradiation of the three spiro [5.5]undeca-1,3-dien-7-ones (1),(2), and (3) leads to two types of annelated bicyclo[3.1.0.]hexen-2-yl ketone products, the structures of which were assigned by n.m.r. spectroscopy and confirmed by X-ray crystallography; the results are interpreted in terms of a substitution-influenced 1,2-acyl shift, involving one or both double bonds, with an oxa-di-π-methane type mechanism.