TRIALKYLSULFONIUM AND TETRAALKYLAMMONIUM SALTS AS HYDROGEN-BONDING CATALYSTS IN AN AZA-DIELS-ALDER REACTION: EXPERIMENTAL AND COMPUTATIONAL STUDIES

Hydrogen-bonding catalysis by cyclic trialkylsulfonium and tetraalkylammonium salts Among the examined in an onium aza-Diels-Alder reaction salt catalysts, cyclic tetrakis[3,5-bis(trifluoromethyl)phenyl]borate possessing a was investigated. trialkylsulfonium non-coordinating counter anion was the most effective. Details of the activation modes of cyclic trialkylsulfonium and tetraalkylammonium salts were discussed on the basis of DFT calculation.