Oxirene participation in the photochemical Wolff rearrangement

Evidence obtained by carbon labelling and carbene-scavenging techniques for the establishment of an alpha-oxocarbene-oxirene interconversion in the photolysis of acyclic alpha-diazoketones is summarised. Normal-sized alicyclic alpha-diazoketones and o-quinone diazides react without intervention of the oxirene route, whereas the 12-membered ring system behaves like the acyclic counterparts. The oxirene participation is discussed with reference to stereochemical features of the alpha-diazoketones and predictions derived from high-level theory.