Base- Mediated [2+4] Annulation of Benzothiazolium Salts and 2-Aminobenzaldehydes: Selective Synthesis of 2-Amino and 2-Thio- Substituted Quinolines

Abstract

A transition-metal-free [2+4] cyclization reaction of benzothiazolium salts with 2-aminobenzaldehydes has been developed, enabling the selective synthesis of N-substituted and S-substituted quinoline derivatives. The chemoselectivity is primarily controlled by the choice of base and solvent, which selectively cleave either the C–S or C–N bond in the resulting spirocyclic intermediates. This approach demonstrates excellent chemoselectivity, environmental friendliness, and high step economy.