Selective Reduction of Azines to Benzyl Hydrazones with Sodium Borohydride Catalyzed by Mesoporous Silica‐Supported Silver Nanoparticles: A Catalytic Route towards Pyrazole Synthesis

摘要: The catalytic activity of supported silver nanoparticles on mesoporous silica was studied, for the selective reduction azines into benzyl hydrazones using sodium borohydride as mild reducing agent. Different sizes (Ag/HMS) were successfully prepared by two methods, i.e. wet impregnation followed with hydrogen at 350oC and in situ deposition/reduction a mixture amines (ethanolamine ethylenediamine). Ag/HMS (amines) catalyst found to promote 1,2-reduction aryl-substituted azines, compared corresponding 1,4-reduction that occurs general processes. This transfer hydrogenation process be clear, fast quantitative (>99% yields selectivity) towards synthesis under conditions. Of great importance is present conditions reducible functional groups remain intact. Formal kinetics, support formation silver-hydride species being responsible process. presence protic polar methanol enhanced Ag/HMS. Based recycling studies system Ag/HMS-NaBH4 catalyze nine times without significant loss its activity. Finally, one-pot reaction between produced series nitrostyrenes readily provided regioselective 1,3,5,-subtituted pyrazoles, highlighting useful synthetic application protocol.