Nitrogen containing compounds are of great importance because of their interesting and diverse biological activities. The construction of the C–N bond is of significant importance as it opens avenues for the introduction of nitrogen in organic molecules. Despite significant advancements in this field, the construction of the C–N bond is still a major challenge for organic chemists, due to the involvement of harsh reaction conditions or the use of expensive catalysts in many cases. Thus, it is a challenge to develop alternative, milder and cheaper methodologies for the construction of C–N bonds. Herein, we have selected some prime literature reports that may serve this purpose.

C–N bond forming cross-coupling reactions: an overview

As two coexisting and fast-growing research fields in modern synthetic chemistry, the merging of organocatalysis and C–H bond functionalization is well foreseeable, and the joint force along this line has been demonstrated to be a powerful approach in making inert C–H bond functionalization more viable, predictable, and selective. In this review, we provide a comprehensive summary of organocatalysis in inert C–H bond functionalization over the past two decades. The review is arranged by types of inert C–H bonds including alkane C–H, arene C–H, and vinyl C–H as well as those activated benzylic C–H, allylic C–H, and C–H bonds alpha to the heteroatom such as nitrogen and oxygen. In each section, the discussion is classified by the explicit organocatalytic mode involved.

Organocatalysis in Inert C–H Bond Functionalization

The Complementary Competitors: Palladium and Copper in C-N Cross-Coupling Reactions

Primary and N-alkyl arylamine motifs are key functional groups in pharmaceuticals, agrochemicals, and functional materials, as well as in bioactive natural products. However, there is a dearth of generally applicable methods for the direct replacement of aryl hydrogens with NH2/NH(alkyl) moieties. Here, we present a mild dirhodium-catalyzed C-H amination for conversion of structurally diverse monocyclic and fused aromatics to the corresponding primary and N-alkyl arylamines using NH2/NH(alkyl)-O-(sulfonyl)hydroxylamines as aminating agents; the relatively weak RSO2O-N bond functions as an internal oxidant. The methodology is operationally simple, scalable, and fast at or below ambient temperature, furnishing arylamines in moderate-to-good yields and with good regioselectivity. It can be readily extended to the synthesis of fused N-heterocycles.

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Dirhodium-catalyzed C-H arene amination using hydroxylamines.

Metal organic frameworks (MOFs) are fascinating materials for diverse applications due to their adjustability of aperture and structure Herein, a three-dimensional iron-based MOF with BDC linker (BDC = 1,4-benzenedicarboxylate), commonly known as MIL-53(Fe), has been synthesized and successfully composited with anionic resin (Amberlite IRA 200) and cationic resin (Amberlite IRA 900) resulting solid composite photocatalysts, AMIL-53 (Fe) and DMIL-53(Fe), respectively In the novel composite photocatalysts, bulky MIL-53(Fe) MOF solids are used as both a support to anchor the finely ground Amberlite IRA resin powders and as a visible light active component for the degradation of organic pollutants in water In addition to being a traditional support, the resins here were used as a co-catalyst (with loading ration of the resin to MIL-53(Fe) is controlled around 20 wt%) to capture and transfer pollutant molecule from bulk solution into the active centers of the composited catalysts Such an immobilization of the resins significantly alters MIL-53 (Fe) activity and degradation selectivity of dye pollutants; after 120 min of visible light illumination (λ ≥ 420 nm) removal yield of SRB (24%) by the bare MIL-53 (Fe) was apparently improved to 96% after MIL-53 (Fe) was modified by Amberlite IRA 900, DMIL-53(Fe) The tunable degradation order was demonstrated by employing AMIL-53 (Fe) for the selective degradation of cationic dyes while DMIL-53 (Fe) for the degradation of anionic dyes Furthermore, the composites activity was optimized by controlling resin to MOF ratio during immobilization Immobilization also improves ease of separation and recyclability of the original MOF Especially, AMIL-53 significantly reduces iron ion leaching resulting in an enhanced stability The photocatalytic mechanism under visible-light irradiation is also discussed

Resin modified MIL-53 (Fe) MOF for improvement of photocatalytic performance

One-pot aromatic amination based on carbon–nitrogen coupling reaction between aryl halides and azido compounds

Palladium on carbon-catalyzed solvent-free and solid-phase hydrogenation and Suzuki–Miyaura reaction

Solvent-free Huisgen cyclization using heterogeneous copper catalysts supported on chelate resins

10% Palladium on carbon (10% Pd/C) successfully catalyzed the intramolecular C−H amination of various N-mesylated 2-aminobiphenyls in the presence of a catalytic amount of pyridine N-oxide in heated dimethyl sulfoxide (DMSO) under an oxygen atmosphere to afford the corresponding N-mesylcarbazoles. The reaction would proceed via a single-electron transfer process based on its significant suppression by the addition of a single-electron scavenger, tetracyanoquinodimethane (TCNQ), and the substituents on the aromatic rings of the substrate have an insignificant effect on the reaction progress.

Kei Nozaki

Papers

One-pot aromatic amination based on carbon–nitrogen coupling reaction between aryl halides and azido compounds

Palladium on carbon-catalyzed solvent-free and solid-phase hydrogenation and Suzuki–Miyaura reaction

Solvent-free Huisgen cyclization using heterogeneous copper catalysts supported on chelate resins

Palladium on Carbon-Catalyzed C−H Amination for Synthesis of Carbazoles and its Mechanistic Study

Development of chelate resin-supported palladium catalysts for chemoselective hydrogenation