Regio-and stereoselectivity in the halogenation of methyl tricyclo[4.1.0.02,7]heptane-1-carboxylate

Conjugate halogenation of methyl tricyclo4.1.0.0^2,7]heptane-1-carboxylate by the action of N-iodoand N-bromosuccinimides in the presence of halide ions occurs exclusively at the central bicyclobutane C¹–C⁷ bond via electrophilic attack on the C¹ atom, leading to endo,syn-adducts of the norpinane series. Reactions of the title compound with iodine, dibromotetrachloroethane, and (dichloro-λ³-iodanyl)benzene give not only the corresponding 6,7-endo,syn-dihalonorpinane but also its epimer at C⁶, indicating radical mechanism of the halogenation. The regio-and stereoselectivity observed in these ionic and radical reactions are discussed in terms of the results of nonempirical MP2/STO-3G calculations of appropriate cationic and radical intermediates.