Transition metal-catalyzed C-H bond activation strategy is a prominent approach towards the synthesis of various drug-like candidates and biologically active scaffolds. Among the various types of transformations involving the C-H bond activation reaction, the Catellani reaction occupied a special space in organometallic chemistry. Catellani reaction was first discovered by Marta Catellani in the year 1990, which uses palladium (Pd) and norbornene (NBE) as co-catalyst. While traditional norbornene was limited to only some methodology, the inherent modification was done later on by the Glorious group and Dong group for the selective o-amidation and o-alkylation of aryl sp2 C-H bonds with rhodium and palladium catalysts. The key feature of norbornene is its rigid structure that restricts β-hydride elimination and facilitates C-H bond activation. Borrowing the concept from Dong’s work, we envisaged whether monocyclic, non-rigid, commercially available, and dead cheap maleimide could serve as a suitable mediator in Catellani reaction or not? In addition, only second and third-row transition metals have been employed in the Catellani reaction that provides an opportunity to demonstrate the uncovered reactivity of earth-abundant, eco-friendly and cheaper first-row transition metal. To uncover this elusive space, we have demonstrated a synthetic protocol, that is ortho amidation of phenol in presence of cationic cobalt catalyst and maleimide as co-catalyst. After several tedious trials, we have successfully demonstrated Catellani reaction was found successful with first-row metal cobalt and monocyclic olefin. Further, detailed mechanistic study, DFT calculation validates the proposed mechanism. It is found that the reaction is operating through a Co(III)-Co(V)-Co(III) manifold. The catalytic system works efficiently with different electronically biased substrates as well as with complex bioactive molecules.

Breaking the monotony: Cobalt/maleimide a new entrant to Catellani reaction in intramolecular C-H amidation of phenol

ACS Spring 2022

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