Chiral diphosphites derived from (1R,2R)-trans-1,2-cyclohexanediol: a new class of ligands for asymmetric hydrogenations

Abstract

A series of novel chiral diphosphite ligands was easily prepared in a few steps from commercial (1R,2R)-trans-1,2-cyclohexanediol as the chiral source, and successfully employed in the Rh-catalyzed asymmetric hydrogenation of α,β-unsaturated carboxylic acid derivatives and enamides with up to 99% ee for dimethyl itaconate and enamides and with up to 94% ee for α-dehydroamino acid esters. The stereochemically matched combination of (1R,2R)-trans-1,2-cyclohexanediol backbone and (S)-binaphthyl in the ligand (1R,2R)-bis[(S)-1,1′-binaphthyl-2,2′-diyl]phosphitecyclohexanediol, was essential for inducing high enantioselectivity. Moreover, the sense of enantiodiscrimination of the products was mainly determined by the configuration of the binaphthyl moieties.