Tris(pentafluorophenyl)borane Catalyzed Carbenium Ion Generation and Autocatalytic Pyrazole Synthesis - A Computational and Experimental Study.

In recent years, metal-free organic synthesis using triarylboranes as catalysts has become a prevalent research area. Herein we report a comprehensive computational and experimental study for the synthesis of highly selective N-substituted pyrazoles through the generation of carbenium species from the reaction between aryl esters and vinyl diazoacetates in presence of catalytic tris(pentafluorophenyl)borane [B(C6F5)3 ]. DFT studies were undertaken to illuminate the reaction mechanism revealing that the in-situ generation of a carbenium species acts as an autocatalyst to prompt the formation of N-substituted pyrazoles regiospecifically in good to excellent yields (up to 81%).