Studies On The Acetyloxylation And Dimethoxymethylation Of N-Heterocyclic C-H Bonds

Nitrogen-containing heterocycles have enormous practical importance in many fields, including medicines, pesticides, functional materials, and so on. Direct C-H activation and functionalization of nitrogen heterocycles have received widely attention due to their great advantages, such as excellent regioselectivity, minimized reaction steps, low cost, and high atom-economy. In this thesis, recent developments in the direct C-H activation and functionalization of N-heterocycles were summarized, including those transition metal-catalyzed or transition-metal-free C-H activation and functionalization. On the basis of previous studies, this thesis focuses on the exploration of direct C-H functionalization reactions of N-heterocycles in the presence of palladium catalysis or under transition-metal-free conditions. Thus, this dissertation includes the following two parts:1. A synthesis of quinoxaline derivatives through palladium-catalyzed quinoxalinyl group-directed acetyloxylation of ortho C-H bonds has been developed. This method provides a procedure for the synthesis of quinoxaline derivatives based on the direct C-H acetyloxylation from simple and easy availability starting materials, which exhibits high regioselectivity with excellent yields.2. Then, a K2S2O8-mediated direct dimethoxymethylation of nitrogen heterocycles by methanol has been developed, thus allowing for a concise and regiospecific synthesis of N-heterocycle carbaldehyde dimethyl acetals. This method has some advantages, such as transition-metal-free, aldehyde-free, acid-free, and high yield. The mechanistic studies demonstrated that the reaction may proceed via oxygen-participated radical process involving multi-fold bond cleavage of C-H, C-O, and O-H bonds. In addition, the structure of the resulting N-heterocycle carbaldehyde dimethyl acetals has been confirmed by X-ray diffraction analysis.