Quinaphos and Dihydro‐Quinaphos Phosphine–Phosphoramidite Ligands for Asymmetric Hydrogenation

Abstract

New derivatives of the Quinaphos ligands and the related Dihydro-Quinaphos ligands based on the more flexible 1,2,3,4-tetrahydroquinoline backbone have been prepared and fully characterised. A general and straightforward separation protocol was devised, which allowed for the gram-scale isolation of the R(a),S(c) and S(a),R(c) diastereomers. These new phosphine-phosphoramidite ligands have been applied in the Rh-catalysed asymmetric hydrogenation of functionalised olefins with the achievement of excellent enantioselectivities (> or = 99%) in most cases and turnover frequency (TOF) values of up to > or = 20,000 h(-1). These results substantiate the practical utility of readily accessible Quinaphos-type ligands, which belong to the most active and selective category of ligands for Rh-catalysed hydrogenation known to date.