H-bonding interactions in the epoxidation of alkenylammonium salts with dimethyldioxirane and m-chloroperbenzoic acid:: A kinetic study

The epoxidation rate constants for the reaction of allylic and homoallylic primary and quaternary ammonium salts with DMDO (Ib) and m-CPBA (2), as well as the stereochemical outcome of these reactions, were determined. The presence of an ionic functional group in the substrate complicates the kinetic study of the reaction. However, k(0) can be determined from the k(obs) values measured in solutions with different ionic strengths. The order of magnitude of the rate constants is the same for the epoxidation of primary and quaternary homoallylic ammonium salts, while primary allylic ammonium salts react more than 10 times faster than their quaternary counterparts. High syn-diastereoselectivity is achieved in the epoxidation of the primary allylic salt 3aH(+) while the quaternary allylic ammonium salt 5a(+) gives equimolecular (m-CPBA) or predominantly anti (DMDO) mixtures of diastereomers. These results are consistent with the existence of hydrogen bond interaction between the protic substrates and the oxidant.