Ab initio studies on the mechanism of the cycloaddition reaction between ketene imine and formaldehyde — catalytic and solvent effects

Ab initio calculations have been used to study the mechanism of the cycloaddition reaction between ketene imine and formaldehyde. In the gas phase, the reaction proceeds via a concerted but asynchronous way; while in dichloromethane solvent, the reaction becomes a two-step zwitterionic one, with the C-C bond formed firstly. The BH3-catalyzed reaction is predicted to be a concerted process, in which BH3 is bonded to formaldehyde. The energy barrier of this process is 12.22 kcal/mol (in the gas reaction) or 13.81 kcal/mol (in the dichloromethane solvent) respectively. They are much lower than that of the non-catalyzed reactions.