Sulfur (VI) Fluoride Exchange (SuFEx) via Glass-Assisted Organocatalysis

An environmentally benign route for the synthesis of sulfonamides via Sulfur (VI) Fluoride Exchange (SuFEx) chemistry utilizing N-methylimidazole, that simultaneously act as a base, precatalyst, HF by-product scavenger, as well as solvent, is described. This one-step sulfonamide synthesis exhibits excellent reactivity toward highly electron-deficient and less nucleophilic anilines as well as aminopyridines while tolerating a wide range of functional groups. In addition to the desired sulfonamide target, we also isolated an ionic salt as the sole side product from the reaction mixture that has been identified as bis[1-methyl-1H-imidazole-3-ium] hexafluorosilicate (IV). The glass surface of reaction vessel is acting as the source of silicon present in the isolated side product. Formation of hexafluorosilicate salt is also facilitating the consumption of sulfonyl fluoride for sulfonamide synthesis. Optimization of the reaction under various conditions, as well as the isolation of the bis[1-methyl-1H-imidazole-3-ium] hexafluorosilicate (IV) salt, highlight the crucial role of N-methylimidazole and support the glass-assisted approach. Besides the first example of glass-assisted SuFEx catalyzed by benign organic bases, this reaction also offers an alternative route for accessing protic hexafluorosilicate-based molten salts without employing external HF. The synthetic utility of this SuFEx route for late-stage functionalization is also demonstrated.