Construction of Heterocycle Scaffolds via Transition Metal‐ Catalyzed sp2 CH Functionalization

Abstract

AbstractRecently, the CH functionalization strategy for the construction of heterocycles has received substantial attention because of its economic, sustainable and environmentally benign features. Many kinds of heterocycles have been synthesized via transition metal‐catalyzed sp2 CH functionalization. The new strategy for the construction of heterocycle scaffolds includes intramolecular cyclizations and intermolecular cyclizations, namely multicomponent reactions (MCRs) that achieve the formation of multiple bonds in one operation. This review introduces the synthesis of carbazoles, benzoxazoles, benzimidazoles, 2‐substituted benzothiazoles, 3‐aryl/alkylindazoles, indoles, oxindoles, indolines, benzolactams, phthalimides, dibenzofurans and bridgehead unsaturated bicyclic enamines by the new strategy. The orientation of the cyclizations depends mainly on steric factors in cases where two regioisomers can be obtained. The regioselectivity of cyclizations is high in most cases, the cyclizations are even exclusive to give one sole product without the regioisomer in some cases. The functional group tolerance is good in most cases, halogen atoms and even iodine atoms are tolerated by the new strategy in some cases, providing a handle for further functionalization. The described strategy is being rapidly developed. Versatile features of the strategy have emerged, this review tries to classify the reported methods and inspire further investigations.