Establishing the Reaction Pathways of the Catalytic Conversion of Erythrulose to Sulphides of Alpha-Hydroxy Thioesters and Esters

Sulphides of alpha-hydroxy thioesters and esters (SAH(T)Es) are important fine chemicals and have great potential as platform molecules. SAH(T)Es are typically synthesized from fossil sources while little is known regarding their synthesis from carbohydrates. We report our findings about the one-pot chemocatalytic conversion of erythrulose (ERU) to SAH(T)Es. Sn, Mo and W chlorides were the most selective catalysts towards the synthesis of S-butyl-4-butylthio-2-hydroxybutanethioate (BBTHBT) in 1-BuSH. The selectivity towards BBTHBT was impacted by the formation of different thioacetals (TAs). The addition of either KOH, H2O or MeOH was effective to decrease TAs formation and increase selectivity towards BBTHBT (or its ester). A kinetic profile, in situ C-13 NMR measurements and experiments at different temperatures complement our studies to unravel the complicated reaction network involved in the conversion of ERU to SAH(T)Es. This insight provides a solid foundation for future improvements in the sustainable synthesis of SAH(T)Es.