Boron-Catalyzed Hydrogenative Reduction of Substituted Quinolines to Tetrahydroquinolines with HydrosilanesThis research was supported by the Institute for Basic Science (IBS-R010-D1) in Korea.
Received: 30 March 2017
Accepted after revision: 09 May 2017
23 May 2017 (eFirst)
Published as part of the Cluster Silicon in Synthesis and Catalysis
A metal-free procedure for the hydrogenative reduction of substituted N-heteroaromatics has been developed by using hydrosilanes as reducing agents. The optimized conditions were successfully applied to the reactions of quinolines, quinoxalines, and quinoline N-oxides. They were also effective for the reduction of quinolines bearing amino or hydroxy groups, where H2 was evolved through dehydrogenative silylation of the amine or hydroxy moieties. Preliminary mechanistic studies revealed that the initial step in the catalytic cycle involves 1,4-addition of the hydrosilane to the quinoline to give a 1,4-dihydroquinoline; this is followed by (transfer) hydrogenation to deliver the tetrahydroquinoline as the final product.