Photochemical Reactions of Regioisomeric 2,2‐Dimethyl‐5,5‐diphenyl‐ and 5,5‐Dimethyl‐2,2‐diphenyl‐Substituted Diazo Ketones of a Tetrahydrofuran Series

Abstract

Abstract The principal direction of conventional photolysis of the regioisomeric 2,2‐dimethyl‐5,5‐diphenyl‐ and 5,5‐dimethyl‐2,2‐diphenyl‐substituted 4‐diazodihydrofuran‐3(2 H )‐ones 1a and 1b , respectively, is the Wolff rearrangement, while other photochemical processes, which are giving rise to the formation of CH‐insertion, 1,2‐alkyl‐ or ‐aryl‐shifts, as well as H‐atom‐abstraction products occur to a much lower degree ( Schemes 2 and 3 ). The ratio of similar reaction products from both regioisomers 1a and 1b is essentially independent of their structure, and a substantial effect of the relative position of the Ph and diazo group to each other on the yield of CH‐insertion products does not occur. Based on stereochemical considerations, the Wolff rearrangement of diazodihydrofuran‐3(2 H )‐ones apparently proceeds in a concerted manner, whereas the appearance in the reaction mixture of 1,2‐shift and H‐atom‐abstraction products points to the parallel generation during photolysis of singlet and triplet carbenes ( Schemes 4 and 5 ).