Mechanism of the Photochemical and Thermal Wolff Rearrangement of 2-Diazo-1,3-dicarbonyl Compounds

Thermolysis and photolysis of 2-diazo-1,3-dicarbonyl compounds were investigated as a function of methanol concentration. As the methanol concentration decreased, methyl group migration increased concomitant with the suppression of O–H insertion into methanol, whereas aryl group migration was essentially unaltered with the methanol concentration. The results are interpreted as indicating that aryl migration occurs directly from the excited state of diazo compounds, but that met hyl migration takes place in the singlet carbene in competition with O–H insertion.