This PhD thesis focuses on new C-C or C-X (X = O, N, S etc.) bond formation reactions, including many different strategies, such as new carbene transfer reactions and photoinduced palladium-catalyzed alkylation-alkynylation of aromatic alkynes. Specifically, transition-metal catalyzed selective sigmatropic rearrangement reactions and gem-difluoro olefination reactions are carefully investigated, which provide unique reactivity and chemoselectivity. The first project realized the

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... d chemoselective sigmatropic rearrangement reactions of sulfides with diazo compounds depending on the substitution pattern and solvent. When electron-deficient pyridyl sulfides reacted with aryl diazoacetate using Rh2esp2 as carbene transfer catalyst and ethyl acetate as the solvent, [2,3]-sigmatropic rearrangement products were obtained with high efficiency; however, when THF was used as the solvent, highly chemoselective [1,2]-sigmatropic products were observed. Furthermore, photochemical transition-metal free carbene transfer reactions are also discussed in this thesis, which provide complementary aspects. Different sigmatropic rearrangement and O-H insertion products could be obtained in high yields under mild photochemical conditions. Then we started the investigation of 1-aryl-2,2,2-trifluorodiazoethane as gem-difluoro alkene precursor with electron-rich arenes, such as indoles and anilines, to achieve a highly efficient gem-difluoro olefination reaction under transition-metal catalyzed conditions. Finally, we started our investigation of dicarbofuncitionalization reaction of aryl alkynes by applying commercially available phenylacetylene and unreactive alkyl halides as substrates. To our surprise, we obtained the unique 1,3-enyne products under photoinduced palladium-catalyzed reaction conditions. This protocol could realize catalytic alkylation-alkynylation reaction in one synthetic step with good stereoselectivity and high efficiency.