A new procedure for oxidative coupling of aromatic and acrylic acids with alkynes has been developed using abundant, nontoxic, and air stable Cp*Co(III) catalyst. The coupling involves initial cyclometalation via weak chelation-assisted C-H bond activation followed by alkyne coordination, insertion, and reductive elimination leading to diverse isocoumarins (α-pyranones) in good yields under mild conditions.

Transition-metal-catalyzed C–H bond functionalizations have had an enormous influence on organic synthesis in recent times. However, the use of low-abundance 4d and 5d metals is almost inevitable, and they are in high demand. This will be a cause of concern, and hence, it is important to develop methods based on 3d metals, which are widely present in the Earth’s crust. In this regard, the use of 3d metal catalysts or their precursors for catalysis, in general, and C–H bond functionalizations, in particular, has gained significant momentum in the recent times. The major development in catalytic C–H bond functionalizations with 3d metals has been achieved predominantly with strongly coordinating directing groups such as pyridyl, pyrimidinyl, pyrazolyl, and 8-amino-quinolinyl groups. Thus, prefunctionalization of substrates with these directing groups is necessary, which contradicts the step- and atom-economy of C–H bond activation. However, commonly available functional groups such as aldehyde, ketone, carboxylic acid, amide, hydroxy, and N-oxides loosely bind to metals through weak-coordination. These weakly coordinating directing groups orient the metal to activate C–H bond regioselectively without the need for preinstalled strongly coordinating directing groups. Although it is challenging, this contemporary topic has been actively pursued by many researchers in recent times. Through this article, we provide a comprehensive overview of 3d metal-catalyzed, weakly coordinating, directing-group-enabled C–H bond functionalizations reported until March 2021.

A novel protocol for ortho-C-H alkylation of aromatic and heteroaromatic ketones and esters under Cp*Co(III) catalysis has been developed for the first time. The reaction proceeds through initial cyclometalation via weak chelation-assisted C-H bond activation, followed by coordination of activated alkene, insertion between Co-C, and protodemetalation.

Cp*Co -catalyzed highly regioselective mono- and bis-annulation of arylamides with 1,3-diynes using N-OMe as an internal oxidant is demonstrated. This atom-economical transformation does not require any external oxidant and tolerates many functional groups. Various symmetrical and unsymmetrical heterocycles (homo and hetero) are accessed with predictable regio- and chemoselectivity.

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