Cobalt–Nitrenoid Insertion-Mediated Amidative Carbon Rearrangement via Alkyl-Walking on Arenes

Abstract

We herein disclose the Cp*Co­(III)­(LX)-catalyzed amidative alkyl migration using 2,6-disubstituted phenyl azidoformates. Upon the cobalt–nitrenoid insertion toward the substituted ortho carbon, an arenium cationic species bearing a quaternary carbon is generated, and a subsequent alkyl migration process is suggested to occur through an unforeseen alkyl-walking mechanism. A quinolinol ligand of the cobalt catalyst system is proposed to facilitate the final product-releasing rearomatization process by serving as an internal base. This new mechanistic mode enabled both [1,2]- and [1,4]-alkyl rearrangements to allow the structural variation of N-heterocyclic compounds.

Alcohol-Incorporating Diels–Alder Dimerization ofIn SituFormedortho-Quinamine via Co-Nitrenoid Insertion

“…To our best knowledge, this result represents the first example of using metal-nitrenoid as a tool to empower the amidative DA dimerization. It should be also emphasized that this outcome is in stark contrast to the previously reported alkyl migratory behavior of the same starting material 1 giving rise to a bicyclic carbamate 2a (60%) in nonafluoro- tert -butanol (NFTB) solvent (entry 2) . Reaction without cobalt catalyst did not proceed at all, and the starting material 1 remained intact (entry 3).…”

“…Recently, our group reported a Co-catalyzed amidative alkyl migration by utilizing 2,6-disubstituted phenyl azidoformates, where cationic arenium species, formed by the putative Co-nitrenoid insertion, was the key intermediate to induce the alkyl migration reactivity (Scheme b) . Meanwhile, Meth-Cohn and co-workers showcased that substituted phenyl azidoformate can undergo a dearomatic DA dimerization through the insertion of pyrolytically generated free nitrene .…”

Multidimensional Screening Accelerates the Discovery of Rhodium Catalyst Systems for Selective Intra- and Intermolecular C–H Amidations

“…Then, the vials were placed under vigorous shaking at room temperature for 10 min for the in situ formation of the premised Cp*M­(LX)Cl complexes. For cobalt catalyst systems, however, separately prepared Cp*Co­(LX)­Cl complexes − were employed instead of using the premixing conditions. The subsequent addition of a solution of substrates 1a – 1c (1.0 equiv) allowed us to set up the multidimensional optimization conditions in a small reaction scale (10 μmol of 1a – 1c ).…”

“…On the other hand, outer-sphere amination reactions featuring C–H insertion or stepwise hydrogen atom transfer and radical rebound process were achieved by engaging an additional LX-type ancillary in the half-sandwich metal complexes. Indeed, our group and others have successfully utilized such piano-stool Ir, − Ru, − and Co − complexes for the selective transfer of in situ generated metal nitrenoids , to enable the outer-sphere C–H aminations. In contrast, to the best of our knowledge, catalytic reactivity of Cp X Rh­(III)­(LX)-type complexes has been unexplored, especially toward the outer-sphere C–H amination reactions (Scheme b, left).…”

Breaking the Monotony: Cobalt and Maleimide as an Entrant to the Olefin-Mediated Ortho C–H Functionalization

“…β-H elimination from intermediate III has been restricted due to the absence of a synperiplanar arrangement of β-H and the metal. Thus, the rigidity of maleimide allows intermediate III to persist and undergo oxidative addition of Co­(III) to the O–N bond, leading to the formation of the Co­(V) nitrene intermediate IV . At this stage, electrophilic addition of nitrogen to the ortho C–H bond generates a dearomatized spirocyclic intermediate V and reduces Co­(V) to Co­(III).…”