Reaction of carbanions generated from arylmethylphosphonates with cyclic enones. Regio- and stereoselectivity of addition

alpha-lithiated benzylphosphonate esters, XC6H4CH(Li)PO3Et2, add regioselec tively to cyclohex-2-enone at the carbonyl group; higher reaction temperatu res lead to the reversal to the starting materials, and not to the 1,4-addi tion. Relative configuration of the C(1) and C-alpha centers in the 1,2-add ucts was determined from the C-13 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 regi oselectivity yielding the 1,4-, but not the 1,2-addition product. The cryst al and molecular structure of that 1,4-adduct has been determined and demon strates that the conformation about the C(1)-C-alpha bond is close to that existing in solution, deduced from the value of the H-1 NMR (3)J(HH) vicina l coupling constant of the H(1)-C(1)-C-alpha-H hydrogens. The same conforma tion was also confirmed as the most stable by molecular modeling.