Studies on New Cross-Coupling Reactions : The Cleavage and Formation of C-C Bonds

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Recently, effective carbon-carbonbond forming reactions have attracted much attention due to their utility for the synthesis of a variety of organic functional materials and biologically active agents. We have successfully developed a number of new catalytic coupling reactions of aromatic and unsaturated compounds which involve carbon-carbon and/or carbon-hydrogen bond cleavage and carbon-carbon bond formation. The purpose of this study is to improve their efficiency and selectivity and to develop other related new reactions. The catalytic reactions of aromatic substrates possessing carboxyl and bydroxyl groups with alkynes or alkenes were initially examined using various late transitionmetal catalysts. During the treatment of aromatic carboxylic acids with internal alkynes under rhodium catalysis, the oxidative 1:1 coupling efficiently proceeded via carbon-hydrogen bond cleavage to selectively give isocoumarin derivatives. On the other hand, in the reaction of same substrates under iridium catalysis, naphthalene derivatives were exclusively formed by the oxidative 1:2 coupling. The latter reaction appears to involve regioselective carbon-hydrogen bond cleavage directed by the carboxyl group and subsequent decarbaxylation. It was also found that the unique removable functional group can induce new coupling reactions around it. Thus, heteroaromatic carboxylic adds possessing indole and thiophene rings smoothly underwent the regioselective vinylation and mylation accompanied by decarboxylation under palladium catalysis. We also examined a number of other related couplings and succeeded to develop them. The results obtained through this study have been reported widely by academic papers and presentations in domestic and international conferences.