It was found that a novel tandem cyclization of sulfonamides 6 possessing an alkene linked to acetylene dicobalt complex and a benzene ring proceeded smoothly to tricyclic compounds containing medium sized cyclic amines. The stereochemistry depends on the substitution pattern of benzene ring. Treatment of 6a having no activating group on benzene ring with BF3-Et2O afforded a trans-tricyclic compound 7 in high yield. On the other hand, the tandem cyclization of 6b with 3',4'-dimethoxy benzene gave a cis-tricyclic compound 9. Subjection of 6c with 3',5'-dimethoxy benzene to the acidic conditions at -78oC resulted in a direct cyclization of benzene to iminium ion producting a 11-menbered cyclic amine 11 in 71 % yield.
