Dimethyl (2-chloromethyl-2-propenyl)phosphonate (3b) and (tert-butyl)[2-(chloromethyl)-2-propenyl](phenyl)phosphane oxide (3d) were prepared and their reactions with α,β-unsaturatedesters 5a−c and ketone 5d, acting as phosphorylated trimethylenemethane equivalents by a [3+2] strategy, were investigated. With the use of LDA in the presence of DMPU, the Michael addition proceeded with high stereoselectivity