Study On Arylation Of Heterocycle C-H Bonds Catalyzed By CuO Nanospindles

Heterocycles are one of the most important structural motifs of the organic compounds and are ubiquitous in pharmaceuticals, dyes, pesticides and organic materials. Searching efficient methods for the synthesis of heterocycles and their corresponding derivatives have been the goals of many chemists. Transition metals complexes have been widely studied as the efficient and powerful catalysts for the synthesis of heterocycles. The C–H functionalization of the heterocycles is one of the most important methods.This dissertation mainly discussed CuO nanospindles catalyzed arylation of heterocycle C–H bonds. The main contents are just as follow:1. The study on the reactions of heterocycle C–H bonds and aryl iodides catalyzed by CuO Nanospindles.CuO nanospindles were prepared through a simple method using Cu(OAc)2, NH3·H2O and NaOH, and were characterized by XRD,SEM,TEM analysis. Next, we studied the catalytical properties of the CuO nanospindles in the arylation of heterocycle C–H bonds. The optimization of the reaction conditions was performed using benzoxazole and iodobenzene as substrates. The result showed that CuO nanospindles could efficiently catalyze the reaction without ligands using diglyme as solvent and K2CO3 as base under reflux in good yields. Under the optimized reaction conditions, we screened the scope of the substrates, and the results showed that benzoxazole, benzothiazole and 1-methylbenzimidazole can react with aryl iodides containing various functional groups such as OMe, COOEt and CN under the conditions in good yields. 21 corresponding products were obtained and characterized by 1H NMR, 13C NMR, and HRMS.The mechanism for the CuO nanospindles-catalyzed direct arylation of heterocycle was investigated. XRD and EDS analysis of the catalysts after the reaction demonstrated that the catalysts had no change during the reaction process. Leaching of the copper from the CuO nanospindles after the reaction was examined by AAS analysis, and a slight leaching (< 1 ppm) was observed. The H/D exchange of the benzothiazole has also been carried out. The result indicated that the hydrogen at C-2 of the heterocycle can be removed in the presence of K2CO3 without the copper catalyst. Therefore, the reaction was believed to occur on the surface of the CuO nanospindles via a heterogenous process, and undergo through an oxidative addition, subsequent anion substitution, followed by a reductive elimination.Compare to the methods reported in the literatures, more environmentally friendly mild base can be used under a ligand-free catalytic condition, and it not only cuts the cost but also protects the environmental to some extent. It is noteworthy that CuO nanospindles could be recycled and have the potential as an ideal catalyst for the industrial production because of their stability and availability.2. The study on the reactions of heterocycle C–H bonds and aryl bromides catalyzed by CuO nanospindles.We also investigated the reactions of heterocycle C–H bonds and aryl bromides catalyzed by CuO nanospindles based on their good catalytical properties. No desired product was obtained in the absence of the ligands, and the good yields were received using triphenylphosphine as ligand. The further optimizations of the reaction conditions are still under the investigation.