Ligand-Controlled Ni(0)–Al(III) Bimetal-Catalyzed C3–H Alkenylation of 2-Pyridones by Reversing Conventional Selectivity

Palladium-Catalyzed Weak Chelation-Assisted Site-Selective C-H Arylation of N-Aryl Pyridones via 2-fold C-H Activation

Palladium-catalyzed weak chelation-assisted oxidative cross-dehydrogenative coupling of arenes has been accomplished. The use of medicinally important pyridones as the intrinsic directing group, regioselectivity, 2-fold C-H activation, and late-stage modification of bioactive compounds are the important practical features.

Copper-Catalyzed Regioselective Imidation of 2-Pyridones

We demonstrate a ligand- and glovebox-free regioselective direct C(3)-H imidation of 2-pyridones and also benzylic-type imidation of 2-pyridones bearing a methyl substituent employing Cu(OAc)2·H2O as the catalyst and N-fluorobenzenesulfonimide (NFSI) as an imidating reagent. A broad range of imidated 2-pyridone derivatives is made up to excellent yields. The present strategy operates well on a gram scale, and the ensuing product can be readily subjected to mono- and bis-desulfonylation reactions.

Controllable Skeletal and Peripheral Editing of Pyrroles with Vinylcarbenes

The skeletal editing of azaarenes through insertion, deletion, or swapping of single atoms has recently gained considerable momentum in chemical synthesis. Here, we describe a practical skeletal editing strategy using vinylcarbenes in situ generated from trifluoromethyl vinyl N-triftosylhydrazones, leading to the first dearomative skeletal editing of pyrroles through carbon-atom insertion. Furthermore, depending on the used catalyst and substrate, three types of peripheral editing reactions of pyrroles are also disclosed: α- or γ-selective C-H insertion, and [3+2] cycloaddition. These controllable molecular editing reactions provide a powerful platform for accessing medicinally relevant CF3-containing N-heterocyclic frameworks, such as 2,5-dihydropyridines, piperidines, azabicyclo[3.3.0]octadienes, and allylated pyrroles from readily available pyrroles. Mechanistic insights from experiments and density functional theory (DFT) calculations shed light on the origin of substrate- or catalyst-controlled chemo- and regioselectivity as well as the reaction mechanism.

Intermolecular Carbophosphination of Alkynes with Phosphole Oxides via Ni-Al Bimetal-Catalyzed C-P Bond Activation

Intermolecular carbophosphination reaction of alkynes or alkenes with unreactive C-P bonds remains an elusive challenge. Herein, we used a Ni-Al bimetallic catalyst to realize an intermolecular carbophosphination reaction of alkynes with 5-membered phosphole oxides, providing a series of 7-membered phosphepines in up to 94 % yield.

Pd(II)-Catalyzed Oxidative Naphthylation of 2-Pyridone through N-H/C-H Activation Using Diarylacetylene as an Uncommon Arylating Agent

A Pd(II)-catalyzed straightforward oxidative naphthylation of unmasked 2-pyridone derivatives is described using a twofold internal alkyne as a coupling partner. The reaction proceeds through N-H/C-H activation to provide polyarylated N-naphthyl 2-pyridones. An unusual oxidative annulation at the arene C-H bond of the diarylalkyne leads to the formation of polyarylated N-naphthyl 2-pyridones, where the 2-pyridone-attached phenyl ring of the naphthyl ring is polyaryl-substituted. Mechanistic studies and DFT calculations suggest a plausible mechanism based on N-H/C-H activation. The N-naphthyl 2-pyridone derivatives were studied to explore encouraging photophysical properties.

Site-Selective C-H Alkenylation of N-Heteroarenes by Ligand-Directed Co/Al and Co/Mg Cooperative Catalysis

We report herein the design and development of Co/Al and Co/Mg bimetallic catalysts, supported by a phosphine/secondary phosphine oxide (PSPO) bifunctional ligand, for the site-selective C-H alkenylation of nitrogen-containing heteroarenes with alkynes. These catalysts enable the alkenylation of pyridine, pyridone, and imidazo[1,2-a]pyridine derivatives at the C-H site proximal to the Lewis basic nitrogen or oxygen atom, which represents a selectivity profile distinct from that of the previously developed cobalt-diphosphine/aluminum catalyst. The alkenylated products were obtained in moderate to good yields using various heterocycles and differently substituted internal alkynes. Kinetic isotope effect experiments suggest the irreversibility of the C-H activation step, the relevance of which to the rate-limiting step depends on the reaction conditions. Density functional theory calculations indicate that ligand-to-ligand hydrogen transfer is the common mechanism of C-H activation.

Ni-catalyzed benzylic β-C(sp(3))-H bond activation of formamides

The development of transition metal-catalyzed β-C-H bond activation via highly-strained 4-membered metallacycles has been a formidable task. So far, only scarce examples have been reported to undergo β-C-H bond activation via 4-membered metallacycles, and all of them rely on precious metals. In contrast, earth-abundant and inexpensive 3d transition metal-catalyzed β-C-H bond activation via 4-membered metallacycles still remains an elusive challenge. Herein, we report a phosphine oxide-ligated Ni-Al bimetallic catalyst to activate secondary benzylic C(sp³)-H bonds of formamides via 4-membered nickelacycles, providing a series of α,β-unsaturated γ-lactams in up to 97% yield.

Switching the Reactivity of the Nickel-Catalyzed Reaction of 2-Pyridones with Alkynes: Easy Access to Polyaryl/Polyalkyl Quinolinones

A Ni-catalyzed C6 followed by C5 cascade C-H activation/[2 + 2 + 2] annulation of 2-pyridone with alkynes has been achieved. A change in the reaction pathway was achieved by tuning the reaction conditions and incorporating a directing group. A wide variety of substrates and alkynes are amenable to this transformation. The key to success for this transformation is the use of sodium iodide as an additive. More importantly, we detected the five-membered metallacycle intermediate through HRMS wherein iodide is ligated to the metal.

Ni-catalyzed hydroarylation of alkynes with unactivated β-C(sp2)-H bonds

Hydroarylation of alkynes with unactivated C(sp²)-H bonds via chelated C-H metalation mainly occurs at γ-position to the coordinating atom of directing groups via stable 5-membered metallacycles, while β-C(sp²)-H bond-involved hydroarylation has been a formidable challenge. Herein, we used a phosphine oxide-ligated Ni-Al bimetallic catalyst to enable β-C-H bond-involved hydroarylations of alkynes via a rare 7-membered nickelacycle.

Ru-Catalyzed C-H alkenylation on the arene ring of pirfenidone using pyridone as a directing group

A method to functionalize the arene ring of pirfenidone has been demonstrated using pyridone as a directing group. Unlike the functionalization of the pyridone nucleus, the method demonstrated here is the alkenylation of the N-aryl ring of pirfenidone with internal alkynes using ruthenium catalyst. High functional group tolerance, simple reaction conditions and site-selective functionalization permit the synthesis of new analogues of drugs in a step-economical manner. The data of the control experiments suggest the possibilities of a base-assisted internal electrophilic substitution (BIES) pathway.

Catalytic Transformations of 2-Pyridones by Rhodium-Mediated Carbene Transfer

An enantioselective cyclopropanation reaction of N-substituted 2-pyridones with diazo compounds has been realized by using a chiral rhodium complex as the catalyst, and the corresponding chiral cyclopropanes could be formed in good yields with high enantioselectivities. Moreover, using acceptor-acceptor dimethyl 2-diazomalonate as the carbene precursor, a novel 1,4-rearrangement of a Boc group from N to C has also been discovered under rhodium catalysis.

Nickel-Catalyzed Hydroarylation Reaction: A Useful Tool in Organic Synthesis

This article describes the recent advances in the field of nickel-catalyzed hydroarylation reaction of alkenes, alkynes, and arenes. All reactions proceeded either through internal hydride transfer or in presence of...

Transient Directing Groups in Metal-Organic Cooperative Catalysis

The direct functionalization of C-H bonds is among the most fundamental chemical transformations in organic synthesis. However, when the innate reactivity of the substrate cannot be utilized for the functionalization of a given single C-H bond, this selective C-H bond functionalization mostly relies on the use of directing groups that allow bringing the catalyst in close proximity to the C-H bond to be activated and these directing groups need to be installed before and cleaved after the transformation, which involves two additional undesired synthetic operations. These additional steps dramatically reduce the overall impact and the attractiveness of C-H bond functionalization techniques since classical approaches based on substrate pre-functionalization are sometimes still more straightforward and appealing. During the past decade, a different approach involving both the in situ installation and removal of the directing group, which can then often be used in a catalytic manner, has emerged: the transient directing group strategy. In addition to its innovative character, this strategy has brought C-H bond functionalization to an unprecedented level of usefulness and has enabled the development of remarkably efficient processes for the direct and selective introduction of functional groups onto both aromatic and aliphatic substrates. The processes unlocked by the development of these transient directing groups will be comprehensively overviewed in this review article.

Domino Decarboxylative Arylation and C-O Selective Bond Formation toward Chromeno[2,3-b]pyridine-2-one Skeletons

Practical Pd-catalyzed 2-pyridones were designed to achieve chromeno[2,3-b]pyridine-2-ones. The reaction proceeds through domino nucleophilic addition and decarboxylative arylation, respectively. This methodology offers a moderately efficient approach to construct the bioactive, fused-heterocyclic skeletons via selective C-O bond formation and decarboxylative arylation in a single step with high selectivity and good yields.