Acid-catalyzed Isomerization of 3-Indolyl Sulfides to 2-Indolyl Sulfides: First Synthesis of 3-Unsubstituted 2-(Arylthio)indoles. Evidence for a Complex intermolecular Process

Article abstract of DOI:10.1021/jo00035a029

The acid-catalyzed isomerization of 3-indolyl sulfides 1 to the corresponding 2-indolyl sulfides 4 provides the first synthesis of 3-unsubstituted 2-(arylthio)indoles, a hitherto unattainable class of compounds.When catalyzed by trifluoracetic acid, the isomerisation proceeds mainly via an intermolecular mechanism involving initial disproportionation to a 2,3-indolyl bis-sulfide 5 and an unsubstituted counterpart 6 followed by further interaction if these species to yield the rearranged isomer 4.A mechanism is proposed involving a role for the acid tn the sulfenyl-transfer steps.This type of process also occurs, to a lesser extent, in the polyphosphoric acid catalyzed isomerization.