MODEL-CALCULATIONS OF CHEMICAL INTERACTIONS .6. ORIGIN OF DIASTEREOFACIAL SELECTIVITY IN 1,3-DIPOLAR CYCLOADDITION OF FORMONITRILE OXIDE WITH BICYCLO [2.1.0]PENT-2-ENE AND 2,3-DIOXABICYCLO[2.2.2]OCT-5-ENE

The previous paper in this series, Part 5, gave a novel theoretical an alysis of the origin of diastereofacial selectivity in 1,3-dipolar cyc loadditions and discussed the reactions of formonitrile oxide with nor bornene and cis-3,4-dichlorocyclobutene. The present paper both deepen s that analysis by defining new quantities related to facial interacti ons and describes the successful application of the theory to two new examples, the reactions of formonitrile oxide with bicyclo[2.1.0]pent- 2-ene and 2,3-dioxabicyclo[2.2.2]oct-5-ene, which cover qualitatively different results from those considered in the earlier work. Total and facial repulsion, total and facial delocalization and forming-bond de localization, together with the deformation energy of dipolarophiles a nd 1,3-dipoles and the stabilization energy of vicinal bond-bond inter actions, form the conceptual framework for a detailed and coherent acc ount of the geometry and energy differences between the syn and anti t ransition structures. Facial repulsions and vicinal interactions invol ving the forming bonds and the bonds at the allylic positions are the primary controlling factors of the differential activation energy of s yn/anti cycloadditions of 1,3-dipoles with double bonds incorporated i nto rigid cyclic systems.