One-Pot Intermolecular C-S Self-Coupling of Dimethyl Sulfoxide Promoted by Molybdenum Pentachloride

The reactions between MoCl5 and 1-2 equiv. of a selection of sulfoxides at room temperature in dichloromethane as solvent were studied. The 1: 1 molar reaction between MoCl5 and dimethyl sulfoxide (DMSO) afforded the C-S coupling product [Me2SCH2SMe][MoOCl4] (1), which was isolated in 46 % yield and characterized by analytical and spectroscopic methods and by X-ray diffraction. MoOCl3, SMe2 and HCl were identified as side products. The reactions between MoCl5 and tetrahydrothiophene 1-oxide, nBu(2)SO, MePhSO or (PhCH2)(2)SO yielded the corresponding sulfides and, in the cases of (PhCH2)(2)SO and MePhSO, also C-S activation compounds. According to DFT calculations, the unusual formation of 1 is the consequence of thermodynamically feasible Cl/O interchange between MoCl5 and DMSO, this being a prerequisite for successive C-H bond activation.