SIMILARITY APPROACH TO CHEMICAL-REACTIVITY - REGIOSELECTIVITY IN PERICYCLIC-REACTIONS

The similarity approach recently proposed as a new universal means of the study of pericyclic reactivity was applied to the study of the phe nomenon of regioselectivity. It has been shown that even within a simp le HMO model the approach is able to predict the preferred regiochemis try of various types of pericyclic reactions like polar and semipolar Diels-Alder reactions, 2 + 2 additions, etc. In contrast to alternativ e perturbational theories of regioselectivity this approach is in most cases able-to predict also whether the reaction proceeds as a concert ed one-step process or whether some biradical or zwitterionic intermed iates are involved.