Enantioselective annulation reactions through C(sp2)–H activation with chiral CpxMIII catalysts

Chiral poly(hetero)cyclic compounds are extensively found in numerous bioactive molecules, natural products, and even functional materials. Synthesis of this class of molecules follows tedious classical synthetic procedures in general. Recent advancement of the transition-metal-catalyzed directed C–H bond activation followed by an intra-/intermolecular cyclization reaction provides an upfront approach to the construction of numerous poly(hetero)cyclic compounds. However, synthesis of chiral annulated products remains challenging. In general, chiral annulated products are synthesized by a conventional organocatalytic pathway employing suitable chiral ligand systems. Lack of suitable chiral ligands and difficulties in the design and synthesis of appropriate ligands constrain the exploration of the chemistry. Remarkably, recent advances on chiral transition-metal catalysis and chiral ligand-controlled asymmetric C(sp2)–H bond functionalization chemistry demonstrate a way forward to access chiral annulated products. This review provides an overview of recent advancements in chiral CpxM(III)-catalyzed asymmetric annulation reactions, emphasizing the mechanistic understanding of the developed protocols.