Tris(pentafluorphenyl)boran‐katalysierte Erzeugung von Carbenium‐Ionen und autokatalytische Pyrazol‐Synthese – eine theoretische und experimentelle Studie

Abstract

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 highly selective synthesis of Nsubstituted pyrazoles through the generation of carbenium species from the reaction between aryl esters and vinyl diazoacetates in the presence of catalytic tris(pentafluorophenyl)borane [B(C 6 F 5 ) 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 regiospecific formation of N-substituted pyrazoles in good to excellent yields (up to 81 %).

Activation of Diazo Compounds by Fluorinated Triarylborane Catalysts

“…This was found both experimentally and computationally (Figure 1 ). 31 34 35 By DFT studies the C–N bond in the boron-coordinated diazo ester is longer and weaker (1.334 Å) than in the free uncoordinated diazo ester (1.318 Å). 14 In addition, a shortening of the C–C bond length from 1.470 Å to 1.436 Å was also observed for the O→B adduct.…”