Oxidation of 2,2,3,3-Tetramethyl-1,4-diphenyl-5,6-dithiabicyclo[2.1.1]hexane and Its Oxidation Products: An Important Role of 1,3-Transannular Interaction in the 1,3-Dithietane Part

Oxidation of 2,2,3,3-tetramethyl-1,4-diphenyl-5,6-dithiabicyclo[2.1.1]hexane with m-chloroperbenzoic acid gives two isomeric endo- (4a) and exo-sulfoxides (4b), three S,S′-dioxides (endo, exo-5a, exo, exo-5b, and endo, endo-5c), and an S,S,S′-trioxide (6). The relative reactivity to further oxidation is 4b >> 4a and 5b > 5a, which suggests that the attractive 1,3-transannular interaction operative in 1,3-dithietane part of 4a and 5a decreases the reactivity of 4a and 5a. 4b isomerizes to 4a on standing over silica gel at room temperature and also 5b is converted to 5a on heating. Heating 6 in refluxing toluene yields 3,3,4,4-tetramethyl-1,2-diphenylcyclobutene, 2,5-dimethyl-3,4-diphenyl-2,4-hexadiene, and the isomeric trioxide.