Controlled monohalogenation of phosphonates Part IV. Selective synthesis of monohalomethylenediphosphonates
Résumé
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.
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