Methyl 2-[(diethoxyphosphoryl)methyl]benzoate reacts with several aldehydes to produce an alkenylphosphonate as the major product, together with varying amounts of the expected Horner–Wadsworth–Emmons product, a 1,2-disubstituted E-alkene. Use of a bulky aldehyde or the tert-butyl ester favours the normal HWE product.