The Pictet-Spengler reaction is one of the most useful methods for synthesizing tetrahydroisoquinoline. This reaction is a kind of Friedel-Crafts reaction. We found that an intramolecular Friedel-Crafts reaction of the iminium cation afforded eight- and nine-membered cyclic amines fused with a benzene ring in high yield. Treatment of sulfonamide derivatives with an aromatic ring possessing one or two methyl groups with TMSOTf gave 1,2,3,4,5,6-hexahydrobenzo[c]azocine derivatives in high yields. Moreover, when sulfonamide derivatives having an acetylene cobalt complex moiety were subjected to the same conditions, not only eight-membered cyclic amine but also nine-membered cyclic amine was obtained in high yield.
