Functionalizations of Indoles by Intermolecular Interrupted Pummerer Reaction

A sulfonium species generated from sulfoxide and acid anhydride is a useful reagent for organic synthesis owing to its powerful electrophilicity. Among the various sulfonium-mediated reactions, interrupted Pummerer reaction has been well-investigated recently, which progresses the nucleophilic attack of substrate on sulfur atom of sulfonium such as Swern-type oxidation. Although interrupted Pummerer reactions are reported with various substrate such as alcohols, alkenes, enol ethers, the application to aromatics is limited because of the stability of initially generated arylthionium salts. In contrast, we previously developed intramolecular reaction via arylthionium intermediate for installing nucleophile to indole 2 alpha-position in a one-pot procedure. This reaction was proceeded with special substrate by intramolecular reaction, therefore, it was unexplored as a general synthetic method. This article describes the details of the development of sulfonium species mediated reactions to functionalize indoles by intermolecular interrupted Pummerer reaction.