PM3 CALCULATIONS ON CYCLOADDITION REACTIONS OF DIIMIDE

Molecular orbital calculations for the reaction of E-diimide and buzadiene show three stationary points for concerted cycloaddition. The lowest energy transition species is asymmetrical with the forming sigma-bonds sufficiently similar in length for the reaction to be synchronous. exo-Addition of Z-diimide shows a symmetrical synchronous reaction pathway. endo-Addition reveals two valleys for concerted addition which are related by symmetry. The bond lengths of the forming sigma-bonds are markedly different consistent with an asynchronous pathway. The calculations predict that endo addition is the most energetically favoured mode of addition for Z-diimide and butadiene.