Enantioselective catalytic addition of nitroesters to N-carboalkyloxy imines : a route to quaternary stereocenters

A readily available, low cost bifunctional organic catalyst promoted the addition of nitroesters to imines; in the reaction between 2-nitropropionates and N-Boc protected aldehyde-imines the product bearing a new quaternary stereocenter was obtained in up to 81% ee. The positively charged catalyst was postulated to control the attack of the enolic form of nitroester to imine through a hydrogen bonding network