Tandem reduction–olefination for the stereoselective synthesis of (Z)-α-fluoro-α,β-unsaturated esters

A tandem stereoselective reduction–olefination reaction of ethyl 2-acyl-2-fluoro-2-diethylphosphonoacetate employing NaBH4 in EtOH was developed. The one-pot reaction gave α-fluoro-α,β-unsaturated esters with excellent (Z)-selectivity. A plausible mechanism involving a diastereoselective reduction predicted by the Felkin–Anh model, followed by olefination similar to the Horner–Wadsworth–Emmons reaction, has been proposed.