Exploration of alpha-Diazocarbonyl Compounds for Transition-Metal Catalyzed Carbon-Carbon Bond Formations. Development of Palladium-Catalyzed Stereoselective Synthesis of Trisubstituted Alkenes and the Synthesis of Quaternary alpha,alpha-Heterodiaryl Carb

Transition-metal catalyzed cross-coupling reactions with alpha-diazocarbonyl compounds for C-C bond formation have been explored. Our study demonstrated that alpha-diazocarbonyl compounds can effectively couple with organopalladium(II) complexes, and a reactive palladium-carbene would be formed. It is believed that highly reactive metal-carbene complexes would undergo migratory carbene insertion to afford new organopalladium complexes. In this research, the diazoesters cross-coupling reactions have been exploited for stereoselective synthesis of (E)-alpha,beta-diarylacrylates, which are important scaffolds for some bioactive compounds. In Chapter 2, we developed the Pd-catalyzed cross-coupling of benzyl bromides with diazoesters, and the (E)-alpha,beta-diarylacrylates were obtained in up to 92% yield and >20:1 E-selectivity. The cross-coupling reaction is mediated by the benzylpalladium(II) complexes, which were formed by the classical oxidative addition of the bromides. However, the benzyl bromide reactions suffered from the excessive usage of the diazo reagents and the phosphine ligand.;To develop a more general and environmentally friendly diazoesters coupling reactions, we accomplished the Pd-catalyzed oxidative arylboronic acids coupling of diazoesters to furnish (E)-alpha,beta-diarylacrylates in excellent yields and stereoselectivity. Notably, this reaction exhibits excellent efficiency involving the use of 1.2 equiv arylboronic acids and dioxygen as the sole oxidant. Mechanistically, this catalytic coupling reaction involves arylpalladium(II) intermediates, which were produced by transmetallation with arylboronic acids. Sequential diazoesters coupling and beta-hydride elimination produced the product acrylate and palladium-hydride species, which should be transformed by the action of dioxygen to some catalytically active palladium(II) complexes.;Apart from alkene formation, tandem C-C bond formation at the carbenic center has also been achieved with catalytic diazoesters cross-coupling reaction as the principal step. Analogous to Pd(II) center, d8 arylrhodium(I) complexes would undergo diazoesters coupling reactions. Our study showed that [Rh(cod)OH]2 can effect catalytic cross-coupling of arylboronates and diazoesters to afford oxa-pi-allylrhodium(I) complexes. In the presence of KOtBu and alkyl halides, tandem alkylation of the allyl complexes were achieved leading to the formation of a quaternary stereocenter at the carbenic carbon. Our study demonstrates the versatility of metal-carbene in the development of highly efficient cascade C-C bond formations, which would be useful for creating molecular structures of higher complexity.