Nanoporous Gold-Catalyzed Selective Reduction Of C-O/C-N Unsaturated Bond And Cycloisomerization Of N-Propargyl Amides

Nanoporous metals,as an amazingly active and selective green heterogeneous catalyst,have three-dimensional bicontinuous structures,controlled feature sizes,low density,high surface area,fine electrical and thermal conductivity and reduced stiffness.The ease of simple preparation in combination with high reactivity and selectivity,rather simple recovery,reusability and long-term stability suggested that nanoporous metals are a green and environment-friendly catalyst and are widely used in organic synthesis field.In the second chapter of this dissertation,AuNPore-catalyzed selective reduction of?,?-unsaturated aldehydes is described by using formic acid(HCO2H)as a hydrogen donor.HCO2H has been proven to be an efficient,safe and economical hydrogen source due to its low cost and renewability.Under the optimized conditions,various ?,?-unsaturated aldehydes were reduced to their corresponding allylic alcohols in 76%-98%yields with high selectivity.This modified protocol exhibits good functional groups tolerance,such as methyl,methoxy,trifluoromethyl,carbonyl,and halides(F,Cl,and Br).No Au leached from AuNPore during the reaction,and the catalyst was easily recycled and reused without losing catalytic activity.The chemoselective hydrogenation of ?,?-unsaturated aldehydes was scaled up to the gram scale,the yield obtained was only slightly decreased,specifying that this protocol has good practicability.The AuNPore-catalyzed chemoselective reduction of quinolines with formic acid as a hydrogen source is described in the third chapter of this dissertation.This AuNPore-catalyzed transfer hydrogenation of quinolines also proceeded very smoothly in the presence of low amounts of HCO2H at a relatively low temperature to produce the desired 1,2,3,4-tetrahydroquinolines(py-THQs)in 74%-94%yields.This modified protocol also showed good tolerance for various functional groups,such as methyl,methoxy,carbonyl,and halides(F,Cl,and Br).Mechanistic studies revealed that the AuNPore-catalyzed transfer hydrogenation of quinolines proceeded via a sequence of 1,4-hydride addition,isomerization,and 1,2-hydride addition.This operationally simple experimental protocol offers a practical and environmentally friendly alternative to the currently known methods for the chemoselective reduction of quinolines.An efficient AuNPore-catalyzed cycloisomerization of N-propargyl amides into solely oxazole derivatives in 1,2-dichlorobenzene is described in the fourth chapter of this dissertation.The AuNPore-catalyst is found to be an active and stable heterogeneous catalyst for the molecular transformation of N-propargyl amides into oxazoles.AuNPore as a catalyst in 1,2-dichlorobenzene at 90? for 22 hours were selected as optimized conditions for exploring the scope of the reaction.N-propargyl amides containing electron-donating groups and electron-withdrawing groups were well tolerated under the optimized condition,and the desired oxazole products were obtained in the range of 74%-96%yields.This is the first example of AuNPore-catalyzed cycloisomerization of N-propargyl amides.