A significant improvement in enantioselectivity has been achieved in the 1, 4-additions of diethylzinc to 2-cyclopentenone, 2-cyclohexenone and 5, 6-hydro-2H-pyran-2-one (up to 93%, 98% and 94% ee, respectively) by using a chiral diphosphite–copper catalyst under suitable reaction conditions.