Abstract

Pd/C catalyzed decarboxylation-transfer hydrogenation of quinoline carboxylic acids and transfer hydrogenation of quinolines had been developed for the synthesis of 1,2,3,4- tetrahydroquinolines. These two processes were implemented smoothly using Pd/C (0.9 mol%) as a catalyst with ammonium formate as a hydrogen source in ethanol at 80 °C. The reaction system can also be applied to transfer hydrogenation of benzo[h]quinoline and 2,9-dimethyl-1,10- phenanthroline with good to excellent yields. And the gram scale and recycling of catalyst had been tested with good results. Furthermore, the mechanism of Pd/C catalyzed reduction of quinoline carboxylic acids and quinolines had been proposed.

Keywords: Palladium, Decarboxylation, Transfer hydrogenation, Quinoline carboxylic acids, Tetrahydroquinoline.

Graphical Abstract