Catalytic effect on the mechanism of [2 + 2] polar cycloadditions

Abstract

The Lewis acid-catalysed reaction between hydroxyethylene and acrylaldehyde has been studied by the MINDO/3 method. The potential barriers for the uncatalysed and catalysed reactions are determined by the second and first transition states respectively. The main effect of the catalyst is to advance the first transition state along the reaction co-ordinate and to increase the zwitterionic character of the intermediate. An insight into the catalytic action is obtained.