Studies On Transition Metal-Catalyzed C-H Bond Activation/Functionalization

Transition-metal catalyzed C-H bond activaton/functionalization to construct carbon-oxygen, carbon-halogen, carbon-nitrogen, carbon-carbon, and other carbon-heteroatom bonds has become a hot topic in the organic chemistry field during the past few years. As a novel synthetic strategy, direct C-H bond activation/functionalization features in high atom-economy and regio-selectivity in comparison with the traditional trasition-metal catalyzed cross-couping approaches. Various functionallizations of this type have been finely developed both in effiecient convertion and excellent regioselectivity, which will find widespread application in future.This dissertation includes six chapters as follows:In chapter 1, advantages and advances in C-H bond activation/ functionaliztion was briefly summarized. In this context, the recent development of transition-metal catalyzed directed C-H bond activation/functionalization to install various bonds including carbon-oxygen, carbon-halogen, carbon-nitrogen, carbon-carbon, and other carbon-heteroatom bond linkages was extensively reviewed, which is very relevant to my Ph. D. studyIn chapter 2, a N-ligand directed palladium-catalyzed ortho C-H bond activation mono-nitation approach was developed, which features in: 1) high regio-selectivity, C-H bond nitration was immune from the substituent effects but only occurred at ortho position of the directing groups; 2) broad substrate scope, especially for the substrates bearing acid-sensitive groups such as hydroxyl (OH) and acetoxy (OAc), etc.were well tolerated. In addition, a general method for the preparing of o-nitro acetophenone derivatives was developed based on the present nitration strategy.In chapter 3, an azaarenes-directed selective C-H bond fluorination was described. A novel Pd (OAc)2/NFSI/TFA system was developed for the highly selective ortho-monofluorination of azaarenes e.g., quinoxaline, pyrazole, benzo[d]oxazole, and pyrazine derivatives; on the other hand, alternative di-fluorinated product was obtained by tunning the reaction condition. Furthermore, the reaction was run without the protection against air and moisture. Finally, a Pd (Ⅱ/Ⅳ) catalytic cycle was proposed based on the ESI-MS/MS experiments.In chapter 4, a selective C-H bond fluorination of O-methyl oximes under mild condition was described. The critical nitrate additive efficiently promoted the ortho monofluorinarion under mild condition, while difluorinated product was obtained with an elevated temperature, thus a temperature-controlled selective fluorination was developed. The present protocol was applicable in various 0-methyl oximes including the fluorination of olefinic sp2 C-H bond under ambient conditions of temperature and air.In chapter 5, a novel iron-catalyzed benzylic methylenenation was developed to transfer the carbon atom in "N,N-dimethyl" moiety of DMA (or DMF) to 2-methyl azaarenes thus generating 2-vinyl azaarenes, which are not easily be synthesized by traditional strategies. The vinylaromatics started from simple propiophenone underwent Heck closure to give benzo[α]phenazines. Preliminary mechanistic studies showed a CDC species between substrates and N,N-dimethyl amides was the key intermediates.In chapter 6, all the experiments sections as well as the characterization of the products were displayed.