Summary: The use of trans-2-phenyl-1-vinylcyclopropane as a hypersensitive probe to study the epoxidation mechanisms of monooxygenases and their models is described; the high yield epoxide formation indicates that the Mn (1II) salen mediated epoxidation of unfunctionalized alkylsubstituted olefins is a concerted process. A stepwise mechanism, however, is suggested for the epoxidation of aryl-substituted olefins.
