New developments in the synthesis of heterotopic atropisomeric diphosphines via diastereoselective aryl coupling reactions

Abstract

The new heterotopic atropisomeric diphosphine ( R)-5,6-benzo-2,2′-bis(diphenylphosphino)-4′,5′,6′-trimethylbiphenyl has been prepared. The key step of this synthesis is a diastereoselective, intramolecular aryl–aryl coupling reaction via oxidation of a suitable, chiral diarylcuprate. The catalytic properties of the diphosphine in ruthenium promoted hydrogenations of model substrates and in rhodium promoted 1,4-additions of boronic acids to α,β-unsaturated ketones are fully comparable to those of reference ligands such as BINAP. This seems to indicate that C 2-symmetry is not a structural prerequisite for atropisomeric chiral diphosphines to obtain high enantioselectivities in 1,4-addition reactions as well as in hydrogenation reactions.