Atom economical synthesis of di- and trithiocarbonates by the lithium tert-butoxide catalyzed addition of carbon disulfide to epoxides and thiiranes†
Alkali metal alkoxides were studied as catalysts for the addition of CS2 to epoxides. A screening of several commercially available alkoxides revealed lithium tert-butoxide as an active and selective catalyst for this reaction. The influence of different reaction parameters as well as the substrate scope under optimized reaction conditions has been studied. Terminal and highly substituted epoxides as well as thiiranes were converted. In total 28 products were prepared and isolated in yields up to 95%. Notably, the reactions were performed under mild conditions without additional solvents. The regio- and stereoselectivity of the reaction has been studied e.g. by converting (R)-styrene and (R)-propylene oxide. Moreover, the test reaction was monitored by 13C NMR and a plausible mechanism for the conversion of terminal and internal epoxides is given. This proposal is in agreement with the observed regio- and stereoselectivity of the reaction.