The origin of enantioselectivity in the l-threonine-derived phosphine–sulfonamide catalyzed aza-Morita–Baylis–Hillman reaction: effects of the intramolecular hydrogen bonding

Abstract

L-Threonine-derived phosphine–sulfonamide 4 was identified as the most efficient catalyst to promote enantioselective aza-Morita–Baylis–Hillman (MBH) reactions, affording the desired aza-MBH adducts with excellent enantioselectivities. Density functional theory (DFT) studies were carried out to elucidate the origin of the observed enantioselectivity. The importance of the intramolecular N–H⋯O hydrogen-bonding interaction between the sulfonamide and enolate groups was identified to be crucial in inducing a high degree of stereochemical control in both the enolate addition to imine and the subsequent proton transfer step, affording aza-MBH reactions with excellent enantioselectivity.