Asymmetric Aza-Morita-Baylis-Hillman Reaction Catalyzed by a Phenol-Bearing Phosphine

Significance

A new chiral phosphine Lewis base bearing several phenol groups is described as catalyst for the asymmetric aza-Morita-Baylis-Hillman reaction. It promotes the reaction between N-tosylaldimines and simple Michael acceptors (acrolein, methyl- and ethylvinylketone) with high yields and enantioselectivities under mild reaction conditions. The increase in reactivity and selectivity compared to previously described catalysts is reasoned to originate from multiple stabilizing hydrogen-bonding interactions between the phenolic hydroxy groups and the oxy-anion created by 1,4-addition of the phosphorus. In addition to the catalyst synthesis, this full paper also compares several other catalysts of similar types and reports NMR studies on the reaction intermediates.