Application of a transient directing strategy in cyclization reactions via C–H activation

Abstract

This review introduces the application of a transient directing strategy in cyclization reactions via C–H activation. The types of cyclization reactions include C–H activation/intramolecular C(sp³)–H arylation, C–H activation/intramolecular hydroarylation of alkenes, C–H activation/intramolecular alkene hydroacylation, cyclization through C–C activation and C–H activation in turn, cascade reactions via C–H activation/functionalization and intramolecular nucleophilic addition, cascade reactions via C–H activation/functionalization and intramolecular electrophilic aromatic substitution, and cascade reactions via C–H activation/functionalization and C–N oxidative coupling. These cyclization reactions are catalyzed by Pd, Rh, Ru or Re catalysts. Reactions of the substrates (aldehydes, ketones, a phenol derivative, anilines, etc.) with transient directing groups/reagents (aliphatic amines, aromatic amines, a phosphinite, a secondary amide, an alkyl nitrite, etc.) in situ form directing groups as mono-, bi-, or tridentate ligands assisting C–H activation. Many kinds of carbo-/heterocyclic scaffolds of four-, five-, six-, or seven-membered rings have been constructed. Regio-, chemo- or diastereoselectivities are excellent in most cases. Enantioselectivities are also excellent in some cases where chiral transient directing groups are used. The synthesized cyclic compounds will find applications in pharmaceutical chemistry, material chemistry and synthetic chemistry.