Cu(II)-Catalyzed Functionalizations of Aryl C-H Bonds Using O_2 as an Oxidant

摘要

The development of transition-metal-catalyzed C-H activation reactions directed by functional groups has witnessed substantial progress in the past three decades.A wide range of metal catalysts,including Ru,Rh,Pt,and Pd,has been exploited with varying degrees of success.From the viewpoint of the practicality of these types of reactions in laboratory synthesis and industrial applications,tremendous challenges lie ahead in controlling selectivity and identifying inexpensive oxidants and metal catalysts.In light of the remarkable progress made in the development of Cu-catalyzed C-heteroatom bond forming reactions that were previously catalyzed predominantly by Pd~(II)catalysts,we turned our attention to Cu-catalyzed C-H functionalization reactions.H-abstraction of allylic C-H bonds using Cu(I)/tert-butyl hydroperoxide has been successfully exploited in peroxidation and alkylation reactions.Since the pyridyl group has been extensively used to direct C-H activation reactions,we launched our effort to develop C-H functionalization reactions directed by a pyridyl group (Py)using Cu(II)catalysts.Herein,we report a Cu(II)-catalyzed acetoxylation and halogenation of aryl C-H bonds.This newly discovered reaction is also shown to be applicable to cyanation,amination,etherification,and thioetherification of C-H bonds.