Access to 4-substituted isothiazoles through three-component cascade annulation and their application in C-H activation.

The use of potassium ethyl xanthate (EtOCSk) as a sulfur atom donor enabled the transition-metal-free [3 + 1 + 1] cascade annulation of isopropene derivatives with NHI in DMSO/HO, affording various 4-substituted isothiazoles in moderate to good yields with good functional group compatibility. Furthermore, Pd and Ag-catalyzed C5-H-selective direct oxidation dimerization of 4-substituted isothiazoles afforded 5,5'-bisisothiazoles. This series of reactions included the formation of new C-S, C-N, N-S, and C-C bonds via cascade addition, annulation, and direct C-H activation under mild conditions.