A Study Of Formation Of Aryl-aryl Bond Catalyzed By Palladium Complexes

Aryl-aryl bond exists in natural products such as alkaloids as well as in numerous biologically active parts of pharmaceutical and agrochemical specialties. The formation aryl-aryl bond using homogenous catalysis is one of the most important methods of modern organic synthesis owing to the mild reaction conditions, very good selectivity and high yield. This accord with the tenet of green chemistry.In this dissertation, the direct C-3 arylation of free (NH)-indoles catalyzed by palladium complexes, Suzuki cross-coupling reaction to synthesize biaryls containing N or S atom and Suzuki cross-coupling reaction in water were investigated. A laconic process of direct C-3 arylation of free (NH)-indoles with bromobenzenes and its derivant catalyzed by palladium complexes has been developed. The trait of this process were: the arylation of nitrogen atom in indole can occur without any protection and the functionality of C-3 (cf, halogenation or stoichiometric metalation) prior to arylation reaction was not needed as in literature. The selectivities of C-3/C-2 arylation (～100/1) were almost achieved. These works were not found in literature.The reaction conditions of C-3 arylation reaction were optimized using indole and bromobenzene. Eighteen kinds of 3-arylindoles were prepared under the optimum conditions, among them seven kinds have not been reported yet. The reaction regularity of direct arylation was discovered and summarized. The mechanism of Pd-catalyzed direct C-3 arylation of free (NH)-indoles was investigated and an plausible S_NAr mechanism was proposed according to the experiment results.It was discovered that microwave promoted obviously Pd-catalyzed direct C-3 arylation of free (NH)-indoles with substituted bromobenzenes. The yield of the target product increased over 20% and the reaction time was shortened to 30-45 minutes from 24 hours under microwave heating compared with the normal heating. The reaction efficiency was greatly enhanced but was not found in literature.POPd-catalyzed Suzuki cross-coupling reactions between phenylboronic acid and aryl halides containing hetero atom were successfully realized. The catalytic system tolerated a broad range of functional groups or substrates containing N or S atom. Suzuki cross-coupling of 3-methylthiophenylboronic acid with bromobenzene was optimized and under these optimum conditions, seven kinds biaryls containing -SMe were prepared in high yields, among them five kinds have not been reported yet. POPd-catalyzed Suzuki cross-couplings of phenylboronic acid with 2-bromopyridine were examined and the reaction conditions were optimized. The findings of Suzuki cross-couplings of three kinds of aryl boronic acid with seven kinds of halogenated pyridines testified that POPd had good properties to tolerate substrates containg N and/or S atoms.The effects of various Pd-catalysts and bases on Suzuki cross-coupling of aryl boronic acid with aryl bromides and reuse of POPd were explored. The reaction conditions of phenylboronic acid with 4-chloronitrobenzene in water as the model were optimized. Taking Suzuki cross-coupling of phenylboronic acid with 2-bromothiophene, the effects of various Pd catalysts, bases, PTCs and the ratio of substrates on the reaction were examined and the optimum reaction conditions got.The effects of solvents on Suzuki cross-coupling reactions of phenylboronic acid with 2-bromopyridine, 3-bromopyridine and 2-bromothiazole were investigated respectively. The results indicated that POPds can effectively catalyze Suzuki cross-coupling of aryl boronic acid with aryl halides or heterocyclic halides in water.