The asymmetric 1,4-addition of Et2Zn to 2-cyclohexen-1-one using a Cu(I) salt/N-heterocyclic carbene (NHC)–Ag complex catalytic system afforded optically active 3-ethylcyclohexanone. The reversal of enantioselectivity using the same catalytic system was achieved by changing the order of the addition of substrates.
