Enantioselective organocatalytic epoxidation using hypervalent iodine reagents

A rare example of a hypervalent iodine reagent participating in a 1,4-heteroconjugate addition reaction is reported for the organocatalytic, asymmetric epoxidation of alpha, beta-unsaturated aldchydes using imidazolidinone catalyst 1. Development of an 'internal syringe pump' effect via the slow release of iodosobenzene from an iminoiodinane source provides high levels of reaction efficiency and enantiomeric control in the asymmetric epoxidation of electron-deficient olefins. N-15 NMR studies were conducted to elucidate the reaction pathways that lead to catalyst depletion in the presence of prototypical oxidants. These NMR studies also provided the mechanistic foundation for the application of iminoiodinanes as an internal slow release oxidant to circumvent these catalyst depletion pathways. (c) 2006 Elsevier Ltd. All rights reserved.