Unsupported Nanoporous Gold‐Catalyzed Chemoselective Reduction of Quinolines Using Formic Acid as a Hydrogen Source

Abstract The unsupported nanoporous gold (AuNPore) is demonstrated to be an active and stable heterogeneous catalyst for chemoselective transfer hydrogenation of quinolines using bio‐renewable formic acid (HCO 2 H) as hydrogen source. The AuNPore‐catalyzed transfer hydrogenation of quinolines proceeded smoothly in the presence of low amounts of HCO 2 H at a relatively low temperature to produce the desired 1,2,3,4‐tetrahydroquinolines (py‐THQs) in good to excellent yields. Mechanistic studies revealed that the AuNPore‐catalyzed transfer hydrogenation of quinolines proceeded through a sequence of 1,4‐hydride addition, isomerization, and 1,2‐hydride addition. This operationally simple protocol offers a practical alternative to the currently known methods for chemoselective quinoline reduction.