Transition Metal Catalyzed Free-Amine (−NH<inf>2</inf>) Directed C−H Bond Activation and Functionalization for Biaryl Frameworks

Transition-metal-catalyzed direct transformation of inert C−H bond has revolutionized the arsenal of main-stream organic synthesis, providing a new upfront to forge structurally enriched and biologically relevant scaffolds in a step- and atom-economical way. Past decades have accounted for the major developments in this realm, proclaiming excellent site-selectivity by exploiting a variety of coordinating directing groups (DGs). Consideration of versatile, abundant, sp3-hybridized free-amine (−NH2) functionality for the same purpose has always been a formidable task owing to its innate reactivity. In recent years, free-amine functionality has emerged as a potent DG for a wide range of C−C and C-heteroatom bonds formations and annulation cascades. In this review article, we have discussed the advancements of free-amine directed C−H activation/functionalization reactions towards biaryl frameworks made within a decade (2012 to 2021).