An unusual regiochemistry of reactions of a cyclohexenylphosphonate bearing a β-ethoxycarbonyl group with aldehydes

Reactions of lithiated ethyl 6-(dimethoxyphosphoryl)cyclohex-1-enecarboxylate with aliphatic, aromatic, and unsaturated aldehydes were studied and determined to proceed with α or δ regioselectivity. Such an unusual regioselectivity results from the contribution of two allylic carbanions: one, stabilized by the phosphonate moiety and the other stabilized by the carboethoxy group. The course of the reaction depends mainly on the structure of the aldehyde and the reaction conditions. The products of Horner–Wadsworth–Emmons reaction, including an analogue of some retinol metabolites, were formed under kinetic conditions whereas the δ-adducts were obtained as thermodynamic products.