Oxidation of α-sulfonyl selenides: Formation of selenolesters

Abstract

Treatment of 7-phenylseleno-7,12-dihydrobenzo[5,6][1,3]thiazepino[3,2-a]benzimidazole 6,6-dioxide 7a in CH₂Cl₂ with m-chloroperbenzoic acid (MCPBA) and 28% H₂O₂ at room temperature gave Se-phenyl 2-[(benzimidazol-1-yl)methyl]selenobenzoate 8a. Similarly, the oxidation of sulfone 7a in THF with aqueous Oxone^® at room temperature gave the same selenolester 8a. The formation of selenolesters 8 can be explained by assuming either the involvement of oxaseleniranium cation 13, having a sulfinate group at C-2 of the benzimidazole moiety, as an intermediate which is believed to be formed by an intramolecular nucleophilic attack of the polarized oxygen of the SeO bond of selenoxide 6 to the α-carbon next to the sulfonyl group, or Pummerer-type reactions.