Abstract: A novel concerted electrocyclic ring opening of a jMithiocyclopropyloxirane is described. Metalation of exo-7-bromobicyclo [4.1. O] hept-2-ene anti-oxide (3) with n- butyllithium at 0 OC afforded exo-bicyclo [3.2. 0] hept-6-en-2-ol (4). A mechanism involving conrotatory ring opening of the metalated cyclopropane (6) to (Z, E)-cycloheptadiene oxide 7 followed by conrotatory ring closure is proposed to explain the formation of 4. Evidence for ...