Asymmetric Rh-catalyzed hydrogenation using a furanoside phosphite–phosphoroamidite and diphosphoroamidite ligand library

Abstract

A furanoside phosphite–phosphoroamidite and diphosphoroamidite ligand library L1–L5a–f was tested in the asymmetric Rh-catalyzed hydrogenation of α,β-unsaturated carboxylic acid derivatives and enamides. Enantioselectivity depended strongly on the ligand parameters. High enantioselectivities were obtained in the reduction of dimethyl itaconate (up to >99% ee), α-dehydroamino acid esters (up to 99% ee) and several enamides (up to 92% ee). Kinetic and NMR studies on the intermediates of the catalytic cycle of the reaction indicate that the [Rh(P₁–P₂)(substrate)]⁺ species is the resting state of the reaction and that the rate dependence is first order in rhodium and hydrogen pressure and zeroth order in the substrate.