A DFT study of the Huisgen 1,3-dipolar cycloaddition between hindered thiocarbonyl ylides and tetracyanoethylene

The mechanism for the 1,3-dipolar cycloaddition between the hindered thiocarbonyl ylide and tetracyanoethylene has been studied at the B3LYP/6-31G∗ level. Formation of the [3+2] cycloadduct takes place through a stepwise mechanism that is initiated by the nucleophilic attack of the thiocarbonyl ylide to the ethylene derivative to give a zwitterionic intermediate . The subsequent cyclization of yields a seven-membered cyclic ketene imine , which equilibrates with the thermodynamically more stable [3+2] cycloadduct . The computed free energies are in agreement with the experimental outcomes.