Reductive cleavage of the carbon-sulfur bond by samarium/Cp2TiCl2 system for the synthesis of dialkyl disulfides

Methods for the formation of sulfur-sulfur bond are indispensable tools in synthetic chemistry and biochemistry. Their importance stems from the existence of sulfur-sulfur bond in many molecules such as proteins, peptides, natural products and pharmacologically active compounds.' In addition, disulfides are useful synthetic intermediates in a variety of chemical transformations. (2) In recognition of their importance, various methods for the synthesis of disulfides have been reported, (3) for example the oxidation of thiols (3a), the reaction of alkyl bromides with the sodium hydroxide and sulfur, (3b) the reduction of sulfonic acids and sodium sulfortates, (3c) the reaction of sulfur, borohydride exchange resin with halides, (3g) the reaction of benzyltriethylammonium tetraco-sathioheptamolybdate with alkyl halides. (3h) Thus, most of the methods for the synthesis of disulfides usually require expensive, (3i) unstable and foul reagents, 3a strong base 3b or long reaction time.(3j) The reduction of sulfoxides with active halides 4 and reductive cleavage of sulfur-sulfur bond(5) using samarium/CP2TiCl2 system have been reported. Here, a mild and rapid method for the reductive cleavage of carbon-sulfur bond using samariUM/CP2TiCl2 system, which is a novel method for the formation of disulfides, is described. The carbon-sulfur bond in the alkylthiocyanates was reductively cleaved by samarium/Cp2TiCl2 system to give the corresponding dialkyl disulfides in moderate to good yields (Scheme 1).