An Intermolecular Perturbation Approach to the Cycloaddition of Carbenes toward Olefins. Reaction Path and Stereoselectivity

The perturbation theory of Murrell, Randic and Williams for intermolecular interaction has been combined with the assumption of local zero-differential overlaps. The theory has been applied to the cycloadditions of singlet methylene and halocarbenes toward olefins. The results, obtained by use of the CNDO/2 energies and wave functions for isolated molecules, quantitatively assess the roles of various types of energies influencing the stereochemical courses of reaction. The syn/anti stereoselectivities of halocarbenes in their cycloadditions toward cis-butene-2 are found to be governed by the Coulombic, dispersion, charge-transfer and exchange-repulsion energies altogether. Participation of the d orbitals of the chlorine atom in charge transfer is emphasized.