Iridium catalysts with modular axial-unfixed biphenyl phosphine-oxazoline ligands: asymmetric hydrogenation of alpha,beta-unsaturated carboxylic acids

A series of highly modular chiral axial-unfixed biphenyl phosphine-oxazoline ligands were developed via a simple synthetic route using readily available (S)-(+)-2-phenylglycinol as a starting material. Modular oxazoline motifs can be efficiently constructed through various easily accessible carboxylic acids. These ligands were successfully applied to Ir-catalyzed asymmetric hydrogenation of alpha,beta-unsaturated carboxylic acids to afford chiral alpha-substituted carboxylic acids with excellent results (up to 97% ee, 98% yield, 2000 TON).