Microwave-Assisted Multicomponent Synthesis of Spirooxindole Dihydropyridine Bisphosphonates

A new, simple, catalyst- and solvent-free microwave (MW)-assisted multicomponent method was elaborated for the synthesis of spirooxindole dihydropyridine bisphosphonates as a new family of compounds by the one-pot reaction of isatins, beta-ketophosphonates and primary amines. The synthesis was carefully optimized in respect of the molar ratio of the starting materials, the heating mode, the temperature, the reaction time and the effect of different catalysts. The substrate scope of the synthesis was also investigated, and the novel title compounds could be prepared in moderate to good yields. A proposed mechanism for the multicomponent reaction was also provided, in which the iminophosphonate compound could mean a key intermediate through the formation of the desired spiro derivatives.