Copper-Catalyzed Intramolecular C(sp3)H and C(sp2)H Amidation by Oxidative Cyclization

A practical copper-catalyzed approach to β-lactams via radical carboamination of alkenyl carbonyl compounds

Functionalized β-lactams are highly important motifs in synthetic chemistry. We report an efficient and novel approach to the synthesis of β-lactams via a copper(i)-catalyzed cascade process involving C(benzyl)-H radical abstraction, intermolecular alkene addition, and intramolecular amination reaction. Variously substituted alkenes were synthesized from vinylacetic acid, leading to the corresponding β-lactams in moderate to good yields. Preliminary studies indicate that the reaction undergoes a free radical mechanism via a Cu(i)/Cu(ii)/Cu(iii) catalytic cycle.

Site-selective C(sp3)–H amination of thioamide with anthranils under Cp*CoIII catalysis

Synthetically versatile anthranils as a bifunctional amino source have been employed for the first time to enable direct amination on unactivated C(sp³)–H bonds of thioamides under Cp*Co^III catalysis.

Cobalt-catalysed unactivated C(sp3)–H amination: two-state reactivity and multi-reference electronic character

A remarkable two-state reactivity scenario and an unusual multi-reference character have been computationally found in Co-catalysed C(sp³)–H amination. In addition, the investigation on the additive, aminating reagent, metal center, and auxiliary ligand provides implications for development of new catalytic C–H functionalization systems.

3d Transition Metals for C-H Activation

C-H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C-H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C-H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C-H activation until summer 2018.

European Restrictions on 1,2-Dichloroethane: C-H Activation Research and Development Should Be Liberated and not Limited

Plan B: 1,2-Dichloroethane was recently subject to regulatory controls in the European Union that will severely limit its commercial use. The practitioners of innovative synthetic methods, particularly C-H bond activation, need to investigate alternative solvents if their chemistry is to stay relevant.

Palladium-catalyzed intermolecular amination of unactivated C(sp3)-H bonds via a cleavable directing group

Palladium-catalyzed intermolecular amination of unactivated C(sp³)-H bonds was developed. Using NFSI as both the amino source and the oxidant, this protocol operates under mild conditions with excellent terminal selectivity and a broad substrate scope. Moreover, the directing group can be easily removed to produce 1,2-amino alcohols.

Mechanistic Unveiling of C═C Double-Bond Rotation and Origins of Regioselectivity and Product E/Z Selectivity of Pd-Catalyzed Olefinic C-H Functionalization of (E)-N-Methoxy Cinnamamide

Density functional theory (DFT) calculations have been performed to study the Pd-catalyzed C-H functionalization of (E)-N-methoxy cinnamamide (^E1), which selectively provides the α-C-H activation products (^EP as minor product and its C═C rotation isomer ^ZP' as major product). Three crucial issues are solved: (i) The detailed mechanism leading to ^ZP' is one issue. The computational analyses of the mechanisms proposed in previously experimental and theoretical literature do not seem to be consistent with the experimental findings due to the high barriers involved. Alternatively, we present a novel oxidation/reduction-promoted mechanism featuring the Pd(0) → Pd(II) → Pd(0) transformation. The newly proposed mechanism involves the initial coordination of the active catalyst PdL₂ (L = t-BuCN) with the C═C bond in ^EP, followed by the oxidative cyclization/reductive decyclization-assisted C═C double-bond rotation processes resulting in ^ZP' and regeneration of PdL₂. (ii) The origin of the product E/Z selectivity is the second issue. On the basis of the calculated results, it is found that, at the initial stage of the reaction, ^EP is certainly completely generated, while no ^ZP' formation occurred. Once ^E1 is used up, ^EP immediately acts as the partner of the new catalytic cycle and sluggishly evolves into ^ZP'. A small amount of generated ^ZP' would reversibly transform to ^EP due to the higher barrier involved. (iii) The intrinsic reasons for the regioselectivity are the third issue. The calculated results indicate that the regioselectivity for α-C-H activation is mainly attributed to the stronger electrostatic attraction between the α-C and the metal center.

Rhodium(iii)-catalyzed directed amidation of unactivated C(sp3)–H bonds to afford 1,2-amino alcohol derivatives

A rhodium-catalyzed directed C(sp³)–H amidation to afford 1,2-amino alcohol oxime derivatives has been developed.

Recent advances in β-lactam synthesis

During the past century, β-lactams have been identified as the core of penicillin and since then several strategies have been developed for their synthesis.

Highly mono-selective ortho-methylthiolation of benzamides via cobalt-catalyzed sp2 C–H activation

A highly mono-selective ortho-methylthiolation of benzamides was achieved via Co-catalyzed coupling of benzamides with DMSO.

Nickel-catalyzed regioselective arylation of aromatic amides with aryl iodides enabled by an N,O-bidentate directing group

A bidentate directing group enabled ortho-arylation of C(sp²)–H bonds in aromatic carboxamides with aryl iodides under nickel-catalysis was developed.

Copper-catalyzed α-C–H amidation of simple ethers through C(sp3)–H/N–H cross dehydrogenative coupling

An efficient copper-catalyzed α-C–H amidation of simple ethers with N-(8-quinolyl)amides through C(sp³)–H/N–H cross dehydrogenative coupling was developed.

Copper-Catalyzed Direct Acyloxylation of C(sp2)-H Bonds in Aromatic Amides

Copper-catalyzed ortho-acyloxylation of the sp² C-H bond of aryl amides with carboxylic acids is reported. Benzoic acids, cinnamic acids, and aliphatic acids can be involved, and the desired products were obtained in moderate to good yields. This procedure is compatible with a wide range of functional groups and heteroarenes without the use of any ligands or additives. This method provides an operationally simple approach for the synthesis of benzoate and cinnamate.

Identification of monodentate oxazoline as a ligand for copper-promoted ortho-C-H hydroxylation and amination

The use of a weakly coordinating monodentate directing group for copper mediated ortho-hydroxylation and amination reactions allows for the identification of an external oxazoline ligand as a promoter.

Transition Metal-Catalyzed C-H Amination: Scope, Mechanism, and Applications

Catalytic transformation of ubiquitous C-H bonds into valuable C-N bonds offers an efficient synthetic approach to construct N-functionalized molecules. Over the last few decades, transition metal catalysis has been repeatedly proven to be a powerful tool for the direct conversion of cheap hydrocarbons to synthetically versatile amino-containing compounds. This Review comprehensively highlights recent advances in intra- and intermolecular C-H amination reactions utilizing late transition metal-based catalysts. Initial discovery, mechanistic study, and additional applications were categorized on the basis of the mechanistic scaffolds and types of reactions. Reactivity and selectivity of novel systems are discussed in three sections, with each being defined by a proposed working mode.

Palladium-catalyzed sequential monoarylation/amidation of C(sp3)–H bonds: stereoselective synthesis of α-amino-β-lactams and anti-α,β-diamino acid

Stereoselective synthesis of α-amino-β-lactams via Pd-catalyzed sequential C(sp³)–H monoarylation/amidation is described.

Efficient syntheses of 3-hydroxyimino-1-isoindolinones and 3-methylene-1-isoindolinones via Cu-promoted C–H activation–nitroalkylation–intramolecular cyclization tandem processes

Efficient and selective syntheses of 3-hydroxyimino-1-isoindolinones and 3-methylene-1-isoindolinones were achieved via 8-aminoquinoline assisted Cu-promoted coupling of benzamides with nitroalkanes.

2,4-Diamino-1,3,5-triazine-enabled Cu-catalyzed direct sulfonamidation of aromatic C–H bonds

An efficient copper acetate catalyzed sulfonamidation of arenes via C–H bond activation directed by a 2,4-diamino-1,3,5-triazine chelating group under oxygen as a terminal oxidant has been developed. The reaction shows good regioselectivity and can be performed with a good yield at the gram scale.