&agr;-Lithiated benzylphosphonate esters, XC6H4CH(Li)PO3Et2, add regioselectively to cyclohex-2-enone at the carbonyl group; higher reaction temperatures lead to the reversal to the starting materials, and not to the 1,4-addition. Relative configuration of the C(1) and C&agr;centers in the 1,2-adducts was determined from the13C NMR spectra. For 2-methylcyclohex-2-enone the regioselectivity of the addition is decreased. The lithioderivative of diethyl 1-naphthylmethylphosphonate, C10H7CH(Li)PO3Et2, shows reverse regioselectivity yielding the 1,4-, but not the 1,2- addition product. The crystal and molecular structure of that 1,4-adduct has been determined and demonstrates that the conformation about the C(1)-C&agr;bond is close to that existing in solution, deduced from the value of the1H NMR3JHHvicinal coupling constant of the H(1)-C(1)-C&agr;-H hydrogens. The same conformation was also confirmed as the most stable by molecular modeling.Key words: &agr;-lithiated arylmethylphosphonates, 1,2- vs. 1,4-addition to cyclic enones, steric effects of the cyclohex-2-enone, molecular structure and molecular modelling of the 1,4-adduct of 1-naphthylmethylphosphonate to cyclohex-2-enone.