2-Thianaphthylium ions (1) underwent a polar cycloaddition with 1,3-dienes to afford benzo-fused bicyclic sulfonium salts (2) bearing sulfur atom at bridge-head in excellent yields. The cycloadducts underwent retro-addition reaction to generate the cation (1), which was easily trapped with other diene. Reaction of the adduct (2d) with several nucleophiles caused the ring-opening of (2d) to afford 1-allyl (6) and 1-homoallyl substituted 2-thiochromenes (7) in good yields.