Unsupported Nanoporous Gold Catalyst for Highly Selective Hydrogenation of Quinolines

Abstract

For the first time, the highly efficient and regioselective hydrogenation of quinoline derivatives to 1,2,3,4-tetrahydroquinolines using unsupported nanoporous gold (AuNPore) as a catalyst and organosilane with water as a hydrogen source is reported. The AuNPore catalyst can be readily recovered and reused without any loss of catalytic activity.

Reduction of quinolines to 1,2,3,4-tetrahydroquinolines with hydrosilanes/ethanol catalyzed by TiO2-supported gold nanoparticles under solvent free conditions

“…This method complements a recently presented reduction protocol that uses a nanoporous gold catalyst. 20 The hydrogen atoms in the reduction products arise from hydrosilane (2 C-H bonds on C2 and C4) and from EtOH (C-H bond at C3 and N-H bond). Furthermore, an unexpected exchange of Si-H hydride by protons from solvent can occur under the reaction conditions.…”

“…While our research efforts towards this goal using supported Au NPs were in progress and had reached a level of maturity, an efficient method for the reduction of quinolines by hydrosilanes catalyzed by an unsupported nanoporous gold catalyst was reported. 20 Herein, we present our results which employ hydrosilanes/ethanol as the reducing system under solvent free conditions and Au nanoparticles supported on TiO 2 as the most suitable catalyst. In addition, a stepwise pathway was established with an initially fast 1,2-reduction mode to form 1,2-dihydroquinolines, while the new C2 and C4 hydrogen atoms on reduction products arise from the hydrosilane as supported via labelling experiments.…”

Nanoporous Metals as Novel Catalysts for Chemical Transformations☆

“…Inspired with these results, the same group turned attention to the reduction of quinoline separately. 50 Solvents such as dimethyl formamide and acetonitrile, which were successfully utilized in alkyne reduction, were first studied, but the use of these solvents resulted in low yield of 1,2,3,4-tetrahydroquinoline. After screening of solvents, toluene proved to be the best and gave 91% yield of the desired product (Scheme 13).…”

“…The successful reduction of C]N bond incorporated in aromatic ring such as quinoline 50 inspired us to investigate the reduction of C]N bond of imines. 51 We have found that imines can be reduced selectively with AuNPore/H 2 O/silane system.…”

A polymer supported palladium(II) β-ketoesterate complex as active and recyclable pre-catalyst for selective reduction of quinolines in water with sodium borohydride

“…Examples of transfer hydrogenation catalytic systems active in water for promoting the selective reduction of quinolines and quinoxalines are those based on: a Ni-Al alloy [34], an Ir complex with HCOONa as the hydrogen source [35], a Pd/C and Zn mixture [36], being the majority of transfer hydrogenation catalysts active and selective only in commonly used organic solvents (alcohols, toluene, etc.) [37][38][39][40][41][42][43][44]. However, the major problem related to the recyclability of these transfer hydrogenation catalytic systems in water remains unsolved and the development of more effective, recyclable, and handle-convenient catalysts for this transformation is still highly desirable.…”