Oxidation of 6-tert-butyl-6-phenylpentathiane with trifluoroperacetic acid gave the pentathiane 3-oxide mainly as the monooxide. The 3-oxide takes a twist conformation both in the crystalline state and in solution. Thermal decomposition of the 3-oxide in the presence of 2, 3-dimethyl-1, 3-butadiene yielded both S2O-and S2-transferred products.