Reactions and Rearrangements of 5,6-Disubstituted Bicyclohexenes

Article abstract of DOI:10.1021/jo01294a009

Halogenation of benzvalene (I) with either Br2 or Cl2/CCl4 gives only one adduct, anti,syn-5,6-dihalobicyclo<2.1.1>hexene, IIa or IIb.This adduct is thermally unstable and rearranges to exo,anti-4,6-dihalobicyclo<3.1.0>hexene, IIIa or IIIb (half-life at 50 deg C for IIa = 18 min; for IIb = 77 min).Treatment of IIb with 1 equiv of KCN in aqueous acetonitrile gives anti,syn-5-chloro-6-cyanobicyclo<2.1.1>hexene (IIc) and endo,endo-3,5-dicyanotricyclo<2.2.0.0^2.6>hexane (IVa).IIc slowly rearranges to 6-anti-chloro-4-exo-cyanobicyclo<3.1.0>hexene (IIIc) (calculated half-l ife at 50 deg C = 1E5 min).The mechanism of the rearrangement of IIa-c to IIIa-c in light of kinetic and deuterium-labeling data as well as the mechanism of formation of IIc is discussed.When treated with KOAc in aqueous acetonitrile or AgOAc in benzene, IIb gives endo,endo-3,5-diacetoxytricyclo<2.2.0.0^2.6>hexane (IVb).When IVb is treated with HCl/CCl4, it rearranges to anti,syn-5,6-diacetoxybicyclo<2.1.1>hexene (IId).When heated, both IId and IVb rearrange to exo,anti-4,6-diacetoxybicyclo<3.1.0>hexene (IIId).In contrast, IVa is thermally stable and does not rearrange in acid.