Synthesis of lactones and lactams via C(sp³)-H bond functionalization

The field of directing group-assisted, transition-metal-catalyzed functionalization has undergone a significant transformation, evolving from the use of auxiliary group attachment for the exploitation of native functional groups in novel organic reactions. In particular, coordination-assisted C(sp³)-H bond functionalization has revolutionized synthetic planning to build molecular complexity. Recently, the use of native directing groups in transition-metal-catalyzed reactions has allowed a step-economic process for increased access to biologically important lactones and lactams. Accordingly, lactones and lactams are unavoidable structural motifs with widespread presence in many biological and pharmaceutical arenas, encouraging researchers to access and modify their structures for improved biological properties. In this review, we showcase the diverse aspects of transition metal catalysis, biocatalysis, and photocatalytic C(sp³)-H bond functionalization to access lactones and lactams assisted by carboxylic acid and amines/amides with auxiliary or transient directing groups or unique ligands. This article also emphasizes the role of specially designed complexes, artificial metalloenzymes, and biocatalysts in assembling lactones and lactams. Besides, three-component reactions involving CO as a C1 synthon play a vital role in developing these heterocycles. Importantly, the crucial role of ligands in determining regioselectivity and enhancing enantioselectivity is discussed thoroughly. For better clarity, this review is divided into twelve sections based on the catalysts involved, with subsections categorized by the type of bond activation or formation. Overall, this review aims to inspire the growth of C(sp³)-H bond functionalization, leading to the integration of lactams and lactones in organics.