Regio- and Chemoselective 1,2-Reduction of Quinolines Mediated by Borane and a Base

Selective reduction of readily available quinolines has gained continuous interest in both academia and industry. Described herein is a simple borane (THF·BH3)-mediated 1,2-selective reduction of quinolines in the presence of a simple base under transition-metal-free conditions with high functional group tolerance. Furthermore, this method allows for the facile preparation of N-protected 1,2-dihydroquinolines from commercially available acyl chlorides. The experimental and theoretical studies reveal a reaction mechanism of selective reduction via an intermolecular process that contrasts with the intuitive expectation and traditional concepts. These investigations demonstrate that coordination of borane enables reactivity distinct from that observed in well-studied metal catalysis.