Controlled monohalogenation of phosphonates: Part IV. Selective synthesis of monohalogenomethylenediphosphonates

The preparation of monohalogenated tetraalkyl methylenediphosphonates 5 has been studied. Upon electrophilic halogenation lithiated chloro-, bromo- and iodomethylenediphosphonates 4a–c are selectively prepared from unprotected lithiated methylenediphosphonates 2 whereas the protected ones 3 are unreactive. Condensation of lithiated dihalogenomethanes with diethyl chlorophosphate 7 leads to the formation of lithiated chloro-, and bromomethylenediphosphonates 4a,b. A possible reaction pathway via intermediate carbenoids is proposed.