Use of Vinyl Sulfides in Fischer Indole Reactions

Abstract Vinyl sulfides accessed via Wittig olefination with thioalkylphosphonium salts are used as aldehyde- or ketone surrogates in Fischer indole reactions. These vinyl sulfides react with arylhydrazines in the presence of TsOH·H2O in refluxing ethanol or dichloroethane to yield diverse 3-substituted and 2,3-disubstituted indoles or azaindoles. The utility of this chemistry is highlighted with the efficient preparation of three biomedically relevant compounds: 4-aza-melatonin, a furoindoline, and an indomethacin-like CRTh2 antagonist.