Studies On Transition Metal Catalytic Reactions Of Nitrogen-containing Aromatic Compounds

Nitrogen-containing aromatic compounds are important family in organic chemistry and have important applications in the preparations of natural products, drugs and chemical materials. Therefore, development of synthetic methods for nitrogen-containing aromatic compounds is an important and interesting project. In past decades, great progesses have been made for this purpose. In this dissertation, several novel synthetic methods were studied, by which nitrogen-containing aromatic compounds including ortho-arylated pyridines, arylated piperidines, aryl-substituted indolizines and triarylamines were prepared. We have obtained some important results as follows:A novel Pd-catalyzed direct ortho-arylation of N-phenacylpyridinium bromide was developed. Its unique feature is that the activating group can depart from the arylated pyridines automatically. A kinetic isotope effect study proved that the reaction went through a C-H bond activation pathway. The results from experiments and DFT calculations indicated that the N-phenacyl group played two crucial roles: 1) activation of the pyridine ring by forming an ylid and 2) regioselective control of the arylation by coordination with Pd at the ortho-position of pyridine.A simple and efficient Pd/C-PtO₂ bimetallic catalytic hydrogenation system for the hydrogenation of arylated pyridines was developed. In the present of geminal dichloroalkane, Pd/C has strong ability in hydrodechlorination reactions and PtO₂ is an ideal catalyst for the reduction of pyridine nuclei. Thus, a series of arylated piperidines were prepared by hydrogenation of arylated pyridines smothly under mild conditions.A novel catalytic method for the synthesis of 2,3-diaryl-substituted indolizines was developed. Thus, a series of 2,3-diaryl-substituted indolizines were prepared from 2-methyl-N-phenacylpyridinium bromide and bromo-aromatics in the present of Pd(OAc)₂/PPh₃ in one-pot reaction. The method characterized with simple procedures, mild conditions, and high yields, which is an important addition for the existed methods in the synthesis of indolizines.A convenient synthestic method for triarylamines was developed, by which highly steric triaryl amines were prepared smoothly at room temperature by using Cu(OAc)₂ as catalyst and o-aminophenol and aromatic bronic acids as substrates. The contional experiments proved that the hydroxyl group in o-aminophenol is necessary.Finally, a general and efficient procedure for the preparation of phenols was developed by a copper-catalyzed direct hydroxylation of arylboronic acids at room temperature in water. The method is characterized by the use of a cheap catalyst, mild conditions, simple performance, short reaction time and high yield results.