Selective Synthesis of Non‐Aromatic Five‐Membered Sulfur Heterocycles from Alkynes by using a Proton Acid/N‐Chlorophthalimide System

A multicomponent strategy to achieve two different regioselectivities from alkynes, isothiocyanates and H2O with a proton acid/N‐chlorophthalimide (NCPI) system is described to selectively obtain non‐aromatic five‐membered sulfur heterocycles (1,3‐oxathiol‐2‐imines/thiazol‐2(3H)‐one derivatives) through multiple bond formations. The process features readily available starting materials, mild reaction conditions, broad substrate scope, good functional‐group tolerance, high regio‐ and chemo‐ selectivities, gram‐scale synthesis and late‐stage modifications. Mechanistic studies support the proposal that the transformation process includes a combination of H2O and isothiocyanate, free‐radical formation, carbonation and intramolecular cyclization to give the products. Furthermore, the 1,3‐oxathiol‐2‐imine derivatives possess unique fluorescence characteristics and can be used as Pd2+ sensors with a “turn‐off” response, demonstrating potential applications in environmental and biological fields. Under a proton acid/N‐chlorophthalimide (NCPI) system, two classes of important non‐aromatic heterocycles (1,3‐oxathiol‐2‐imine and thiazol‐2(3H)‐one) are selectively obtained from alkynes, isothiocyanates, and water by slightly changing the reaction conditions. Readily available starting materials, broad substrate scope, gram‐scale synthesis, late‐stage modification, and the potential of 1,3‐oxathiol‐2‐imine derivatives as Pd2+ sensors demonstrate the utility of this method.