The microwave (MW)-assisted addition of dialkyl phosphites to α-oxophosphonates was investigated and optimized under solventless conditions to provide the phenyl- and benzyl-hydroxy-methylenebisphosphonates efficiently by suppressing the rearrangement side reaction. Methyl-hydroxy- methylenebisphosphonates with mixed ester functionalities and an analogous diester-diacid were also synthesized. It was found that the α- oxophosphonates may also be converted to hydroxy-methylenebisphosphonates and/or rearranged products without using dialkyl phosphite as the reagent and with the careful exclusion of water, simply on standing at room temperature, on thermal treatment, or on MW irradiation. These novel reactions taking place via the controlled decomposition of the precursor and resulting in the intermediate formation of dialkyl phosphite were also studied in detail.
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