An Update on Direct C–H Bond Functionalization of Nitrogen-Containing Fused Heterocycles

This report highlights the recent advances in direct C–H bond functionalization of 5,5- and 6,5-fused heterocycles containing at least two nitrogen atoms. Besides C–C bond formation, C–N, C–S, C–P, and C–Si bonds can also be created via a metal-catalyzed process. Some examples, where a C–H functionalization approach was applied for the synthesis of drug candidates, will be presented as well. 1 Introduction 2 C–H Functionalization Reactions of N-Containing Heterocycles 2.1 Imidazo[1,2- a ]pyridines 2.2 Pyrrolo[1,2- a ]pyrazines 2.3 Imidazo[1,2- b ]pyrazoles 2.4 Imidazo[1,2- a ]pyrimidines 2.5 Imidazo[1,2- a ]pyrazines and Imidazo[1,5- a ]pyrazines 2.6 Imidazo[1,2- b ]pyridazines 2.7 Imidazo[4,5- b ]pyridines and Imidazo[4,5- c ]pyridines 2.8 Pyrazolo[3,4- b ]pyridines 2.9 Pyrazolo[1,5- a ]pyrimidines 2.10 Pyrrolo[2,3- d ]pyrimidines and Pyrrolo[3,2- d ]pyrimidines 2.11 Imidazo[1,2- b ][1,2,4]triazines 2.12 Imidazo[1,2- b ][1,2,4,5]tetrazines 3 Outlook 4 Conclusion