Metal-free organocatalytic S-formylation of thiols using CO₂

S-formylation of thiols is achieved via an enzymatic process catalysed by formate dehydrogenase enzyme that fixes CO₂ onto substrates, which plays a crucial role in regulating important biological pathways in living organisms. The achievement of this reactivity through a chemical approach could also be advantageous, which would allow the fixation of CO₂ on a diverse range of thiols. Here we demonstrate a chemical process to prepare S-formyl thiols from CO₂ using a mesoionic N-heterocyclic olefin under metal-free conditions. This catalytic reaction is used to diversify a variety of biologically active thiols obtained from natural terpenoids, fatty alcohols, antioxidants, and commercially accessible analgesic and anti-inflammatory medication molecules, as well as preparation of ¹³C-labelled formyl coenzyme A. Furthermore, we establish a one-pot S-formylation-olefination process for the synthesis of vinyl sulfides under completely metal-free conditions in the presence of CO₂. Overall, this study provides a platform to transform thiols and CO₂ into value-added products.