Several γ, δ-unsaturated sulfinyl compounds were prepared and their reactions with p- toluenesulfonic acid were examined. Conformationally rigid γ, δ-unsaturated sulfinyl compounds such as endo-(alkylsulfinyl) norbornene or 1-(alkylsulfinyl)-2- isopropenylbenzene derivatives afforded 1, 3-oxathianes through intramolecular Pummerer rearrangement.