Manganese-Catalyzed Hydrogenative Desulfurization of Thioamides

Earth-abundant transition metal catalysis has emerged as an important alternative to noble transition metal catalysis in hydrogenation reactions. However, there has been no Earth-abundant transition metal catalyzed hydrogenation of thioamides reported so far, presumably due to the poisoning of catalysts by sulfur-containing molecules. Herein, we described the first manganese-catalyzed hydrogenative desulfurization of thioamides to amines or imines. The key to success is the use of MnBr(CO)(5) instead of commonly-employed pincer-manganese catalysts, together with simple NEt3 and CuBr. This protocol features excellent selectivity on sole cleavage of the C=S bond of thioamides, in contrast to the only known Ru-catalyzed hydrogenation of thioamides, and unprecedented chemo-selectivity tolerating vulnerable functional groups such as nitrile, ketone, aldehyde, ester, sulfone, nitro, olefin, alkyne and heterocycle, which are usually susceptible to common hydride-type reductive protocols.

Automated summary

Earth-abundant transition metal catalysis has been developed as a viable substitute for noble transition metal catalysis in hydrogenation reactions. However, the hydrogenation of thioamides using earth-abundant transition metals has not been reported due to catalyst poisoning by sulfur-containing molecules. In this study, we successfully achieved manganese-catalyzed hydrogenative desulfurization of thioamides to amines or imines by employing MnBr(CO)(5) instead of commonly-used pincer-manganese catalysts, along with NEt3 and CuBr. This reaction demonstrated excellent selectivity in breaking the C=S bond of thioamides, unlike the only known Ru-catalyzed hydrogenation of thioamides, and it exhibited unprecedented chemo-selectivity towards vulnerable functional groups.