Ruthenium Catalyzed Reduction of Nitroarenes and Azaaromatic Compounds Using Formic Acid

Abstract

Various nitroarenes having chloro, methyl, or methoxy substituents were reduced to the corresponding aminoarenes in high yields using formic acid in the presence of a catalytic amount of RuCl₂(PPh₃)₃. For example, 4-chloronitrobenzene was converted in 99% conversion with 98% selectivity at 125 °C for 5 h. 4-Nitroacetophenone was reduced chemoselectively to 1-(4-nitrophenyl)ethanol in 74% isolated yield under the same reaction conditions. Formic acid could also be employed as reductant for hydrogenation of heterocyclic compounds such as quinoline, indole, and quinoxaline in the presence of the ruthenium catalyst. 2-Methylquinoline was hydrogenated to 1,2,3,4-tetrahydro-2-methylquinoline in 93% conversion with 100% selectivity.