Chiral diphosphites derived from d-glucose in the copper-catalyzed conjugate addition of diethylzinc to cyclohexenone

A series of diphosphite ligands 1–3 derived from readily available d-(+)-glucose and bisphenol or binaphthol derivatives have been applied as ligands in the Cu-catalyzed 1,4-addition of diethylzinc to cyclohexenone. Excellent reaction rates (TOF>1200 h⁻¹) and good enantioselectivities (e.e. of up to 84%) were achieved. The modular nature of these ligands allows easy systematic variation in the configuration of the stereocenters (C(3), C(5)) at the ligand backbone and in the biaryl substituents, so the optimum configuration for maximum enantioselectivity in the asymmetric 1,4-addition can be determined. The results obtained show that the enantioselectivity induced by the ligand depends strongly on the absolute configuration of the C(3) stereogenic centre, while the sense of the enantiodiscrimination is predominantly controlled by the configuration of the biaryl groups of the phosphite moieties.