Base‐free Synthesis of S‐Alkyl Isothioureas Through Ring‐opening Reaction of Sulfonium Salts with Isothiocyanates and Amines

A convenient and base‐free three‐component reaction has been developed for the synthesis of S‐alkyl substituted isothioureas from cyclic sulfonium salts, isothiocyanates, and amines. This protocol provides an alternative avenue to access a series of S‐alkyl substituted isothioureas in moderate to good yields through ring‐opening reaction of aryl, alkenyl and alkynyl sulfonium salts. The present strategy features operational simplicity, good functional group tolerance, gram‐scale synthesis and high reaction efficiency.