Oxirene Participation in the Photochemical Wolff Rearrangementa

Evidence obtained by carbon labelling and carbene-scavenging techniques for the establishment of an α-oxocarbene-oxirene interconversion in the photolysis of acyclic α-diazoketones is summarised. Normalsized alicyclic α-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 α-diazoketones and predictions derived from high-level theory.