Studies Of Palladium And Rhodium-Catalyzed C-H Bond Activation

C-H activation has been intensively investigated owing to its atom-economic advantages. In particular, chelation-assisted C-H fuctionalization has emerged as a powerful method for the effective and regioselective construction of a number of pharmaceuticals and bioactive molecules. This dissertation mainly focused on the transition metal-catalyzed chelation-assisted C-H bond functionalization. The contents were listed as follows:1. Thioether as directing group for the palladium-catalyzed direct arylation of arenesThioether is one of the most important functional group and exist in many bioactive compounds, natural products, functional materials and organocatalysts. However, the C-H activation using thioether as dericting group was rarely reported. We reported a practical palladium-catalyzed ortho-arylation of arenes using thioether as the directing group. Importantly, the thioether group can be readily removed or converted to other useful functional groups. The intermolecular kinetic isotopic effect studies reveal that the C-H cleavage of arenes might be the turnover-limiting step.2. Palladium-catalyzed decarboxylative coupling of a-oxocarboxylic acids with2-aryloxypyridinesTransition metal-catalyzed decarboxylative cross-coupling has emerged as a powerful strategy to form carbon-carbon bond. Particularly, a-oxocarboxylic acid is a readily available acyl anion equivalent that is widely utilized in decarboxylative cross-coupling reaction. We reported an efficient palladium-catalyzed decarboxylative ortho-acylation of2-aryloxypyridines with a-oxocarboxylic acids. In this transformation, the aromatic C(sp2)-H bond was successfully acylated to give diverse aromatic ketones regioselectively in moderate to good yields. The pyridine group can be removed easily after the acylation to give the corresponding2-hydroxy aromatic ketones. The intramolecular kinetic isotope effects studies reveal that the C-H cleavage of arenes might be the turnover-limiting step.3. Synthesis of2,3-dihydro-1H-indazoles by Rh(III)-catalyzed C(sp2)-H cleavage of arylhydrazines The indazole is an important heterocycle and the key motif of anti-cancer, anti-inflammatory, anti-HIV, and anti-emetic drugs. Consequently, the diverse approach to indazoles has attracted much attention over the past decades. We reported a rhodium-catalyzed efficient method for the synthesis of2,3-dihydro-1H-indazoles. The reaction of arylhydrazines with olefins results in the corresponding2,3-dihydro1H-indazoles with exclusive regioselectivity via C-H bond activation. The utility of the methodology is illustrated by a rapid synthesis of1H-indazoles under mild reaction conditions.