Sulfur-Sulfur Bond-Driven Synthesis of 3-Thiooxindoles Using Triflic Acid without a Metal or Hydride Source

A triflic acid-catalyzed, metal-free protocol has been developed for the synthesis of 3-thiooxindoles from readily available isatin and thiophenol derivatives under mild conditions, thereby avoiding the use of fluorinated solvents, silanes, and additives. The method exhibits a broad substrate scope with moderate to good yields. In addition, the strategy enables thioether formation from ketones via 3,3-bis(aryl/alkylthio) indolinone, highlighting mechanistic versatility in an acidic medium. Experimental evidence from intermediate and mechanistic investigations substantiates the reaction pathway. Further derivatizations led to antimicrobial compound II, demonstrating synthetic utility.