An efficient and straightforward method has been developed for the synthesis of β-benzyl-substituted 5-membered heterocyclic carbaldehydes via transient directing-group-enabled direct γ-C(sp 3 )−H arylation of 3-methylheteroarene-2-carbaldehydes. A wide range of 3-methylheteroarene carbaldehydes undergo coupling with a variety of aryl iodides, including less reactive iodo pyridine derivatives to provide a library of highly selective functionalized products in good to excellent yields. Some of these products have been successfully utilized in synthesizing useful synthetic intermediates.

The realization of the direct CH bond functionalization has really brought the radical change in planning the organic synthetic strategies via traditional logics. The CH bond functionalization is an art of selective functionalization even in presence of more reactive functional groups. In this article, we have highlighted more challenging intermolecular site‐selective CH bond functionalization of unactivated CH bonds of small organic scaffolds using different diazo carbonyl reagents, substrates, and catalysts‐controlled processes. This article has covered the selective and undirected CH functionalization of alkanes, arenes, N ‐substituted and free aromatic amines, phenols, naphthols, 1,3‐dicarbonyl compounds, and benzofurans with different diazo carbonyl compounds under metal catalysis. This article has been written to serve as a guide for understanding the principle and for accessing newer approaches to achieve the selective CH bond functionalization.