Cycloaddition Reactions of Allenes with N-Phenylmaleimide. A Two-Step, Diradical-Intermediate Process

Article abstract of DOI:10.1021/ja00377a022

The stereoselectivities, chemoselectivities, relative reactivities, and kinetic isotope effects have been determined in the cycloaddition reactions of substituted allenes with N-phenylmaleimide.The comparison of these results with those derived from the studies of the cycloaddition of 1,1-dichloro-2,2-difluoroethene and the radical-chain addition of benzenethiol to allenes strongly indicates that the cycloadditions with N-phenylmaleimide occur via a two step, diradical-intermediate process.The stereochemical features controlling the formation of the stereoisomeric diradical intermediates and their ring closures are discussed.In addition to the cycloaddition processes, competitive ene reactions occur to produce intermediate dienes, which react further to produce 1:2 adducts or nonreactive alkyne-containing 1:1 adducts.These ene reactions also appear to proceed via diradical intermediates.