TCT-DMSO/DMSO- <i>d</i> ₆ Mediated a Mild Thioalkylation and Regioselective Intramolecular Cyclization Cascade to Access 3-Methylthiolated Indoles

A novel and facile method for the synthesis of methylthiolated indole derivatives is presented, relying on the activation of DMSO/DMSO- d 6 by trichlorotriazine (TCT), which is the most cost-efficient, readily available, and stable reagent for DMSO activation to date. In addition, this process is proposed to involve an unprecedented DMSO stabilized methylsulfenium intermediate, derived from the TCT-DMSO/DMSO- d 6 system, promoting metal-free, regioselective intramolecular cyclization.