Formation of Seven-Membered Rings by Ring-Closing Metathesis of Vinyl Bromides

A Grubbs II catalyst mediated ring-closing metathesis (RCM) of monobrominated dienes is reported to proceed in moderate to good yields (40-80%) where the linking chain contains five atoms, leading to carbocyclic and heterocyclic seven-membered bromoolefins. Notably, RCM to form five-, six-, or eight-membered bromoolefins was unsuccessful, with the exception of one example where RCM afforded diethyl 3-bromocyclohex-3-ene-1,1-dicarboxylate. In this case, a bromomethyl-substituted cyclohexene was obtained as a byproduct. The utility of selected bromoolefin RCM products was demonstrated through their participation in Suzuki-Miyaura reactions. Vinylic halide exchange (Br -> Cl) was noted as a side reaction under RCM conditions.