Synthesis of Aryl and Arylmethyl Phosphonates by Cross-Coupling of Aryl or Arylmethyl Halides (X = I, Br and Cl) with Diisopropyl H-Phosphonate

An efficient and generally applicable protocol for the palladacycle-catalysed arylation or K2CO3-promoted arylmethylation of diisopropyl H-phosphonate has been developed. The remarkable features of the palladacycle-catalysed arylation reaction include wide substrate scope (aryl iodides, bromides and chlorides), significant shortening of the reaction time (2 or 3 h) and a low catalyst loading of 1 mol-%. Note that with the base K2CO3 as promoter, arylmethylation could be achieved without any palladium catalyst. Moreover, the first example of a palladium-catalysed phosphonation of inactive electron-rich aryl chlorides with tBuOK as the base has been realized. This result could be considered an important improvement and complement to earlier work of Montchamp and Han, whose catalytic systems are typically compatible with electron-deficient and electron-neutral aryl chlorides.