Selective synthesis of cyclic dithiocarbonates using bis-benzimidazolate salts as multifunctional catalysts

Abstract

Cyclic dithiocarbonates of the type 1,3-oxathiolane-2-thione were selectively and efficiently produced from the reaction between epoxides and CS2 using disodium bis-benzimidazolate salts as catalysts. We have designed and synthesized this group of three nucleophilic catalysts from the neutral forms of bis-benzimidazole compounds (BBE-Me, BBE-H and BBE-NO2), through simple and efficient procedures. All three catalysts, with aryl substituents possessing different electronic characteristics, were able to selectively catalyze the production of cyclic dithiocarbonates. BBE-Me proved to be the most effective catalyst in the initial screening with 1,2-epoxy-3-phenoxypropane, converting 95 % of the epoxide with 99 % of selectivity for the cyclic dithiocarbonate 1,3-oxathiolane-2-thione. This catalyst was subsequently used to evaluate various reaction parameters and then several epoxides were selectively converted to the respective cyclic dithiocarbonates, under mild conditions, with a low catalyst loading, short reaction times, and in a solvent- and additive-free system. A mechanistic proposal, supported by high-resolution mass spectrometry, demonstrated for the first time that a nucleophilic catalyst in this system can simultaneously activate both CS2 and the epoxide molecule.