Synthesis of diethyl 2-(aryl)vinylphosphonate by the Heck reaction catalysed by supported palladium catalysts

The synthesis of diethyl 2-(aryl)vinylphosphonate through direct Heck coupling reaction of the diethyl vinylphosphonate with aryl or heteroaryl halides catalysed by solid materials ([Pd(NH3)4]/NaY, Pd/C, PdO/SiO2) is reported. After optimising the reaction conditions (1.3mol% [Pd(NH3)4]/NaY, DMF, K2CO3, 110–140°C), various aryl and heteroaryl halides were engaged in this reaction leading in all cases good to high yields. Interestingly, when using activated aryl bromides the palladium loading could be lowered to only 0.25mol%. While highly active when coupling aryl iodides (i.e. only 0.15mol% required), the PdO/SiO2 catalyst was found to be inactive when considering aryl bromides. Deep study of this catalytic material revealed that in the case of aryl bromides, absence of in situ reduction of the catalyst precursor prevents the cross-coupling reaction with this latter material.