Catalytic CH Amination with Unactivated Amines through Copper(II) Amides

Transition-Metal-Catalyzed 1,2-Diaminations of Olefins: Synthetic Methodologies and Mechanistic Studies

1,2-Diamines are synthetically important motifs in organo-catalysis, natural products, and drug research. Continuous utilization of transition-metal based catalyst in direct 1,2-diamination of olefines, in contrast to metal-free transformations, with numerous impressive advances made in recent years (2015-2023). This review summarized contemporary research on the transition-metal catalyzed/mediated [e. g., Cu(II), Pd(II), Fe(II), Rh(III), Ir(III), and Co(II)] 1,2-diamination (asymmetric and non-asymmetric) especially emphasizing the recent synthetic methodologies and mechanistic understandings. Moreover, up-to-date discussion on (i) paramount role of oxidant and catalyst (ii) key achievements (iii) generality and uniqueness, (iv) synthetic limitations or future challenges, and (v) future opportunities are summarized related to this potential area.

Copper-Catalyzed C(sp3 )-Amination of Ketone-Derived Dihydroquinazolinones by Aromatization-Driven C-C Bond Scission

Herein, we describe the development of a copper-catalyzed C(sp³ )-amination of proaromatic dihydroquinazolinones derived from ketones. The reaction is enabled by the intermediacy of open-shell species arising from homolytic C-C bond-cleavage driven by aromatization. The protocol is characterized by its operational simplicity and generality, including chemical diversification of advanced intermediates.

One-Pot Synthesis of Primary and Secondary Aliphatic Amines via Mild and Selective sp3 C-H Imination

The direct replacement of sp3 C-H bonds with simple amine units (-NH2) remains synthetically challenging, although primary aliphatic amines are ubiquitous in medicinal chemistry and natural product synthesis. We report a mild and selective protocol for preparing primary and secondary aliphatic amines in a single pot, based on intermolecular sp3 C-H imination. The first C-H imination of diverse alkanes, this method shows useful site-selectivity within substrates bearing multiple sp3 C-H bonds. Furthermore, this reaction tolerates polar functional groups relevant for complex molecule synthesis, highlighted in the synthesis of amine pharmaceuticals and amination of natural products. We characterize a unique C-H imination mechanism based on radical rebound to an iminyl radical, supported by kinetic isotope effects, stereoablation, resubmission, and computational modeling. This work constitutes a selective method for complex amine synthesis and a new mechanistic platform for C-H amination.

Simple Synthetic Routes to Carbene-M-Amido (M=Cu, Ag, Au) Complexes for Luminescence and Photocatalysis Applications

The development of novel and operationally simple synthetic routes to carbene‐metal‐amido (CMA) complexes of copper, silver and gold relevant for photonic applications are reported. A mild base and sustainable solvents allow all reactions to be conducted in air and at room temperature, leading to high yields of the targeted compounds even on multigram scales. The effect of various mild bases on the N−H metallation was studied in silico and experimentally, while a mechanochemical, solvent‐free synthetic approach was also developed. Our photophysical studies on [M(NHC)(Cbz)] (Cbz=carbazolyl) indicate that the occurrence of fluorescent or phosphorescent states is determined primarily by the metal, providing control over the excited state properties. Consequently, we demonstrate the potential of the new CMAs beyond luminescence applications by employing a selected CMA as a photocatalyst. The exemplified synthetic ease is expected to accelerate the applications of CMAs in photocatalysis and materials chemistry.

The Persistent Radical Effect in Organic Synthesis

Radical-radical couplings are mostly nearly diffusion-controlled processes. Therefore, the selective cross-coupling of two different radicals is challenging and not a synthetically valuable transformation. However, if the radicals have different lifetimes and if they are generated at equal rates, cross-coupling will become the dominant process. This high cross-selectivity is based on a kinetic phenomenon called the persistent radical effect (PRE). In this Review, an explanation of the PRE supported by simulations of simple model systems is provided. Radical stabilities are discussed within the context of their lifetimes, and various examples of PRE-mediated radical-radical couplings in synthesis are summarized. It is shown that the PRE is not restricted to the coupling of a persistent with a transient radical. If one coupling partner is longer-lived than the other transient radical, the PRE operates and high cross-selectivity is achieved. This important point expands the scope of PRE-mediated radical chemistry. The Review is divided into two parts, namely 1) the coupling of persistent or longer-lived organic radicals and 2) "radical-metal crossover reactions"; here, metal-centered radical species and more generally longer-lived transition-metal complexes that are able to react with radicals are discussed-a field that has flourished recently.

Nickel-Catalyzed Alkylarylation of Activated Alkenes with Benzyl-amines via C-N Bond Activation

A nickel-catalyzed alkylarylation of active alkenes with tertiary benzylamines was achieved by charge-transfer-complex promoted C-N bond activation. The reaction proceeded through initial Ni-catalyzed C-N bond activation, followed by sequential radical addition, redox and proton abstraction with cleaved amine moiety in the absence of oxidant, and provides an efficient method to prepare various alkyl-substituted oxindoles and dihydroquinolinones in good yields.

Copper-Catalyzed Oxidative Dehydrogenative C(sp3 )-H Bond Amination of (Cyclo)Alkanes using NH-Heterocycles as Amine Sources

A copper-catalyzed oxidative C(sp³ )-H/N-H coupling of NH-heterocycles with affordable (cyclo)alkanes has been developed. This procedure involves C(sp³ )-N bond formation through a radical pathway generated by homolytic cleavage of di-tert-butyl peroxide and trapping of the radical(s) by copper catalysts. The reaction tolerates a series of functional groups, such as bromo, fluoro, ester, ketone, nitrile, methyl, and methoxy. free-NH-containing indoles, pyrroles, pyrazoles, indazoles, and benzotriazoles are successfully N-alkylated.

A Stable Aminyl Radical Coordinated to Cobalt

A family of cobalt complexes bearing the trop₂ NH [bis(5-H-dibenzo[a,d]cyclohepten-5-yl)-amine] and 2,2'-bpy (2,2'-bipyridine) chelate ligands were prepared and fully characterized. The compounds [Co(trop₂ N)(bpy)], [Co(trop₂ NH)(bpy)]⁺ , and [Co(trop₂ N)(bpy)]⁺ are cobalt complexes interrelated by one-electron redox processes and/or proton transfer. Two limiting resonance structures can be used to describe the paramagnetic complex [Co(trop₂ N)(bpy)]⁺ : [Co^II (trop₂ N^- )(bpy)]⁺ (Co^II amido) and [Co^I (trop₂ N^⋅ )(bpy)]⁺ (Co^I -aminyl radical). Structural data, DFT calculations, and reactivity toward H-abstraction indicate a slightly higher contribution of the aminyl radical form to the ground state of [Co(trop₂ N)(bpy)]⁺ . The results described here complete the series of Group 9 metal aminyl radical complexes bearing the diolefin amine ligand trop₂ NH.

Recent Trends in Copper-Catalyzed C-H Amination Routes to Biologically Important Nitrogen Scaffolds

Nitrogen-containing heterocycles have found remarkable applications in natural product research, material sciences, and pharmaceuticals. Although the synthesis of this interesting class of compounds attracted the interest of generations of organic chemists, simple and straightforward assembly methods based on transition-metal catalysis have regularly been elusive. The recent advancements in the development of C-H functionalization have helped in accomplishing the synthesis of a variety of complex heterocycles from simple precursors. This Focus Review summarizes the recent advances in one particular field: the copper-catalyzed C-N bond formation reactions via C-H bond functionalization to furnish a comprehensive range of nitrogen heterocycles. Applicability and synthetic feasibility of a particular reaction represent major requirements for the inclusion in this review.

Copper-mediated aerobic oxidative synthesis of benzimidazo fused quinazolines via a multicomponent approach

First copper mediated aerobic oxidative multi-component synthesis of benzimidazo[1,2-c]quinazolines has been developed from 2-(2-halophenyl)benzoimidazoles, aldehydes and sodium azide as nitrogen source.

Copper(II) triflate catalyzed amination of 1,3-dicarbonyl compounds

A method to prepare α,α-acyl amino acid derivatives efficiently by Cu(OTf)(2)+1,10-phenanthroline (1,10-phen)-catalyzed amination of 1,3-dicarbonyl compounds with PhI=NSO(2) Ar is described. The mechanism is thought to initially involve aziridination of the enolic form of the substrate, formed in situ through coordination to the Lewis acidic metal catalyst, by the putative copper-nitrene/imido species generated from the reaction of the metal catalyst with the iminoiodane source. Subsequent ring opening of the resultant aziridinol adduct under the Lewis acidic conditions then provided the α-aminated product. The utility of this method was exemplified by the enantioselective synthesis of a precursor of 3-styryl-2-benzoyl-L-alanine.

Evidence for a one-electron mechanistic regime in dirhodium-catalyzed intermolecular C-H amination

Swift and energy efficient conversion of chemical feedstocks to pharmaceuticals and agrochemicals requires the development of new methods to add nitrogen functionality to unfunctionalized organic substrates. Dirhodium-catalyzed insertion of nitrene species into C-H bonds is a promising new method, the main drawback of which is the currently limited understanding of the catalytic mechanism. Herein, cyclic voltammetry and controlled potential electrolysis measurements have enabled us to solve many of the mechanistic mysteries of intermolecular C-H amination catalyzed by [Rh(2)(esp)(2)] (esp=α,α,α',α'-tetramethyl-1,3-benzenedipropanoate). The primary result is that, in addition to a simple nitrene-transfer mechanism that dominates the early stages of the reaction, another mechanism is available that relies on sequential proton-coupled electron transfer steps. Whereas the nitrene-transfer mechanism requires the use of expensive, atom-inefficient oxidants, we show that simple one-electron oxidants such as Ce(4+) may be used to achieve catalytic C-H amination via the one-electron mechanistic regime.