The Studies On Transion-metal-catalyzed C-H Direct Arylation And N-H Oxidative Dehydrogenative Homocoupling

This paper consists of two parts:The first part is the studies on the direct arylation of heterocycles with aryl halides catalyzed by transition metals. The second is about the dehydrogenative homocoupling of N-alkylanilines.In the past decades, studies on transition metal catalyzed direct C-H functionalization have attracted much attentions. By C-H functionalization, C-C or C-hetero bonds can be formed directly with high efficiency, shorter synthetic routes, and minimal environmental impact.In the direct arylation of heterocycles, notable metals such as Pd and Rh catalyst are predominant, and used most frequently. Initially, copper was used as additive in the palladium catalyzed direct arylation of arenas. Now, copper has been employed as catalyst in this field. However, among the numerous copper species, there are no examples of using other copper species except CuI as catalyst in the direct arylation of heteroarenes.Based on previous studies, we developed three cooperative catalytic system:(1) CuX/Pd(OAc)2 cocatalytic system.:In the absence of ligand and addivtive, the direct arylation of heterocycles with aryl iodides can be performed smoothly in the CuX/Pd(OAc)2 catalytic system, affording the desired product with good yields.(2) Cu(II)/Pd(OAc)2/PPh3 cocatalytic system:In this catalytic system, aryl bromides can been used as substrates, and the direct arylation of heterocycles could be undertake under mild conditions. In the absence any of them, the reaction did not occur. (3) Pd/C/Cu heterogeneous catalytic system:Without any ligand and additive, the direct arylation of heterocycles with aryl iodides proceeded smoothly with high yields.The above palladium/copper cocatalytic system have the advantages such as low palladium catalyst loading (1 mol%) as compared to the traditional palladium catalyzed reaction usually requiring 5-10 mol% catalyst loading, ligand and additive free, mild conditions, and high efficiency.The transition metal catalyzed coupling plays an import role in the carbon-carbon bonds formation. In the past decades, studies on this field have greatly improved the efficiency of new bond formation and their applications are also enlarged. The dehydrogenative coupling is superior to the traditional coupling reaction. Various symmetric C-C bonds could be formed by dehydrogenative coupling. Through the dehydrogenative coupling of S-H and Sn-H, the S-S and Sn-Sn bonds can also be formed. However, the N-N bond formation by dehydrogenative coupling is rare.As a main kind of compounds containing N-N bonds, hydrazines are used widely in the field of industry and agriculture, and usually show significant biological activity. Most synthesis of them are based on the compounds containing N-N or N=N bonds, thus suffer from harsh conditions such as multiplicity of steps (protection and deprotection), use of dangerous organolithium agent and low temperature(-78℃). Using CuBr as catalyst, CuO as cocatalyst, TMEDA as ligand, and air as green oxidant, we firstly developed the direct synthesis of hydrazines via N-H bond oxidative dehydrogenation coupling with high efficiency. When 4-methoxyl or ethoxyl alkylanilines were used as substrates, o-semidines were obtained with high yields, it is the first example of direct synthesis o-semidines from N-alkylanilines.