The Intramolecular Reaction of Acetophenone N-Tosylhydrazone and Vinyl: Brønsted Acid-Promoted Cationic Cyclization toward Polysubstituted Indenes

In the presence of TsNHNH2, a Bronsted acid-promoted intramolecular cyclization of o-(1-arylvinyl) acetophenone derivatives was developed, leading to polysubstituted indenes with complexity and diversity in moderate to excellent yields. In sharp contrast with either the radical or carbene involved cyclization of aldehydic N-tosylhydrazone with vinyl, a cationic cyclization pathway was involved, where N-tosylhydrazone served as an electrophile and alkylation reagent during this transformation.