The thermal chemistry of vinyldiazo compounds as a method for the generation of vinylmethylenes

Abstract

The thermal chemistry of a series of substituted 1-aryl-3-methyl-2-phenyl-1-diazobut-2-enes has been examined. These vinyldiazo compounds react in two parallel pathways: cyclization to a 3-aryl-5,5-dimethyl-4-phenyl-5H-pyrazole or loss of nitrogen and cyclization to a 1-aryl-2-phenyl-3,3-dimethylcyclopropene presumably by a vinylmethylene intermediate. The kinetics of these processes reveal quite different substituent effects. The relation of these results to the stability of the vinylmethylene produced and to the singlet photochemistry of cyclopropene derivatives is discussed.