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 wel l as the stereochemical outcome of these reactions, were determined. The pr esence of an ionic functional group in the substrate complicates the kineti c study of the reaction. However, k(0) can be determined from the k(obs) va lues measured in solutions with different ionic strengths. The order of mag nitude of the rate constants is the same for the epoxidation of primary and quaternary homoallylic ammonium salts, while primary allylic ammonium salt s react more than 10 times faster than their quaternary counterparts. High syn-diastereoselectivity is achieved in the epoxidation of the primary ally lic salt 3aH(+) while the quaternary allylic ammonium salt 5a(+) gives equi molecular (m-CPBA) or predominantly anti (DMDO) mixtures of diastereomers. These results are consistent with the existence of hydrogen bond interactio n between the protic substrates and the oxidant.