Efficient Synthesis of β-Hydroxy-α-Amino Acid Derivatives via Direct Catalytic Asymmetric Aldol Reaction of α-Isothiocyanato Imide with Aldehydes

An easily available and efficient chiral N,N'-dioxide-nickel(II) complex catalyst has been developed for the direct catalytic asymmetric aldol reaction of alpha-isothiocyanato imide with aldehydes which produces the products in morderate to high yields (up to 98%) with excellent diastereo- (up to > 99: 1 d.r.) and enantio- selectivities (up to > 99% ee). A variety of aromatic, heteroaromatic, alpha,beta-unsaturated, and aliphatic aldehydes were found to be suitable substrates in the presence of 2.5 mol% L-proline-derived N,N'-dioxide L5-nickel(II) complex. This process was air- tolerant and easily manipulated with available reagents. Based on experimental investigations, a possible transition state has been proposed to explain the origin of reactivity and asymmetric inductivity.