Mechanism of the Photochemical Wolff Rearrangement. The Role of Conformation in the Photolysis of α-Diazo Carbonyl Compounds.

Article abstract of DOI:10.1021/jo01314a010

Investigation of photochemical processes of several α-diazo carbonyl compounds reveals that the Wolff rearrangement to form ketene takes place directly from the singlet excited state of the s-Z conformer whereas the excited state of the s-E conformer dissociates nitrogen to generate singlet carbonyl carbene, which either undergoes characteristic carbenic reactions, e.g., insertion and 1,2-hydrogen shift, or gives rise to ketene.The migratory aptitude as well as the relative efficiency of other competing reactions from singlet carbene is shown to be an important factor in dete rmining which reaction pathway is favored.Substantial amounts of singlet carbene can be formed even under sensitized conditions, presumably via intersystem crossing from initially formed triplet carbene.