MNDO-Cl theoretical study of [2 + 2] cycloaddition of cyclopentyne with ethylene

Abstract

The [2 + 2] cycloaddition reactions of cyclopentyne and acetylene with ethylene have been studied by the MNDO method with a 3 × 3 configuration interaction. Both reactions are predicted to take place stepwise through diradical intermediates. The observed stereospecificity of the cycloadditions of cyclopentyne with olefins is explained on the basis of the extremely short lifetime predicted for the reaction intermediates.