Research On The Synthesis Of Disubstitued Pyridines And Trisubstitued Oxazoles Using NH₄OAc As The Nitrogen Resource

Nitrogen-containing heterocyclic compounds such as pyridines and oxazoles, are the key skeletal structures of many natural products, pharmaceuticals and functional material molecules, as well as reactive intermediates in the synthetic processes. And they have a very wide range of applications in synthetic chemistry, materials chemistry, medicinal chemistry and agricultural chemistry. Therefore, the synthesis of nitrogen-containing heterocyclic compounds such as pyridines and oxazoles attracts widespread interest of chemists, and it has been one of the emphases and hotspots in organic synthesis. With the development of synthetic methodology, a range of synthetic methods of nitrogen-containing heterocyclic compounds with different features have been reported. Still, from the perspective of sustainable development considerations, seeking simple,efficient,economic,green and environmentally friendly synthetic methods which modern synthetic organic chemists have been committed to is still an important research direction. In this context, the present dissertation is mainly focused on cascade reactions and multi-component synthesis of functionalized pyridines and oxazoles derivatives as follows:(1) Research on the synthesis of 2,4-diarylsubstituted-pyridines through a Ru-catalyzed four component reaction. Using ruthenium as the catalyst, the reaction involves two molecules of acetophenone, one molecule of DMF,and one molecule of NH4 OAc. The methyl group of DMF performed as the one carbon source inthe transformation. An ammonium salt NH4 OAc was utilized as the cheap nitrogen resource and oxygen was used as the oxidant. 2,4-diarylsubstituted-pyridines were obtained as the sole products in all cases.(2) Iodine catalyzed three components synthesis of three-aryl-substituted oxazoles. Using iodine as the catalyst, oxygen as the oxidant and acetic acid ammonium as the nitrogen source, diaryl ethyl keone reacted with benzil to get 2,3,5-three-aryl-substituted oxazoles selectively. The reaction may involve condensation of ammonium salt with carbonyl group, benzil C-C bond cleavage to provide benzoyl, and then condensation, oxidation and cyclization to give an oxazole ring. This method is mild and simple, and is easy to operate. We can obtain different 2,3,5-three-aryl-substituted oxazoles selectively through this progress.