The reaction of the 6-exo-oxide of 2,2,4,4-tetramethyl-1,5-diphenyl-6,7-dithiabicyclo[3.1.1]heptane (2) with 2KHSO5·KHSO4·K2SO4 gave the first isolable dithiirane oxide, (1RS, 3SR)-3-phenyl-3-(1,1,3,3-tetramethyl-4-oxo-4-phenylbutyl)dithiirane 1-oxide (1), while the 6-endo-oxide of 2 gave both 1 and its (1RS, 3RS)-isomer 10. Under similar reaction conditions, 2 yielded the first isolable, unoxidized dithiirane, 3-phenyl-3-(1,1,3,3-tetramethyl-4-oxo-4-phenylbutyl)dithiirane (3). The dithiirane 3 was also obtained by treatment of 2 with NaOCl–NaClO4. The X-ray structure analyses were performed for 1, 3, and 10. Treatment of unsymmetrical 8,8-dimethyl-1,9-diphenyl-10,11-dithiatricyclo[7.1.1.02,7]undeca-2,4,6-triene with NaOCl–NaClO4gave 3-[1-(o-benzoylphenyl)-1-methylethyl]-3-phenyldithiirane selectively in good yield. However, 1,3-dithietanes, prepared from adamantane-2-thiones, failed to give the corresponding dithiiranes by treatment with 2KHSO5·KHSO4·K2SO4 or NaOCl–NaClO4. The dithiirane 3 thermally isomerized to 2,2,4,4-tetramethyl-1,5-diphenyl-8-oxa-6,7-dithiabicyclo[3.2.1]octane probably via 2,2,4,4-tetramethyl-1,5-diphenyl-5-thioxo-1-pentanone S-sulfide.