The reaction of 1,2-diols with dimethyl sulfoxide-catalytic molybdenum peroxide in refluxing toluene generally resulted in monoprotection of diols to give 2-methylthiomethoxy-l-ols (Course A) Exceptionally, a) cis-1,2-cyclooctanediol and benzopinacol, and b) 1,2-cyclododecanediol caused C–C bond cleavage (Course B) and monooxidation (Course C), respectively as Scheme 1.