Copper-Catalyzed Oxidative Cross-Coupling of N,N-Dimethylanilines with Heteroarenes under Molecular Oxygen

Recent Advances in Aerobic Oxidative of C-H Bond by Molecular Oxygen Focus on Heterocycles

Aerobic oxidative cross-coupling represents one of the most straightforward and atom-economic methods for construction of C-C and C-X (X=N, O, S, or P) bonds using air as a sustainable external oxidant. The oxidative coupling of C-H bonds in heterocyclic compounds can effectively increase their molecular complexity by introducing new functional groups through C-H bond activation, or by formation of new heterocyclic structures through cascade construction of two or more sequential chemical bonds. This is very useful as it can increase the potential applications of these structures in natural products, pharmaceuticals, agricultural chemicals, and functional materials. This is a representative overview of recent progress since 2010 on green oxidative coupling reactions of C-H bond using O2 or air as internal oxidant focus on Heterocycles. It aims to provide a platform for expanding the scope and utility of air as green oxidant, together with a brief discussion on research into the mechanisms behind it.

Recent developments in the green synthesis of biologically relevant cinnolines and phthalazines

Both cinnolines and phthalazines are heterocyclic compounds which have a wide range of biological activities and pharmacological profiles. This work represents the recent advances in the green synthesis of cinnolines and phthalazines as 1,2 and 2,3-diazanaphalenes were cited. The docking studies and mode of action for key scaffolds were also reported.

Cross-dehydrogenative Coupling of N-Aryl Tetrahydroisoquinolines Catalyzed by an Anthraquinone-containing Polymeric Photosensitizer

This work reports the photocatalytic application of an anthraquinone-containing polymeric photosensitizer (AQ-PHEMA) in the visible light-induced cross-dehydrogenative-coupling of N-aryl tetrahydroisoquinolines with several nucleophiles, including nitromethane, 1-methyl-2-alkyl ketone and dialkyl (aryl) phosphine oxide. The results revealed that the reaction could be catalyzed by AQ-PHEMA efficiently to afford a series of 1-substituted-2-aryl-1,2,3,4-tetrahydroisoquinolines in good to excellent yields with nice substrate tolerance under aerobic conditions at room temperature. The practical application potential was also showcased by a gram-scale synthesis. More importantly, the utilization of AQ-PHEMA as a heterogeneous photosensitizer also showed nice recyclability and reusability of the catalyst, whereas AQ-PHEMA can be easily separated and reused for at least 8 times without significant loss of photocatalytic activity.

Anticancer potential of new 3-nitroaryl-6-(N-methyl)piperazin-1,2,4-triazolo[3,4-a]phthalazines targeting voltage-gated K+ channel: Copper-catalyzed one-pot synthesis from 4-chloro-1-phthalazinyl-arylhydrazones

A series of six 3-aryl-6-(N-methylpiperazin)-1,2,4-triazolo[3,4-a]phthalazines were prepared through a facile and efficient one-pot copper-catalyzed procedure from 4-chloro-1-phthalazinyl-arylhydrazones with relatively good yields (62-83%). The one-pot copper-catalytic procedure consists of two simultaneous reactions: (i) a direct intramolecular dehydrogentaive cyclization between ylidenic carbon and adjacent pyrazine nitrogen to form 1,2,4-triazolo ring and, (ii) a direct N-amination on carbon-chlorine bond. Then, an in vitro anticancer evaluation was performed for the synthesized compounds against five selected human cancer cells (A549, MCF-7, SKBr3, PC-3 and HeLa). The nitro-derivatives were significantly more active against cancer strains than against the rest of tested compounds. Specifically, compound 8d was identified as the most promising anticancer agent with significant biological responses and low relative toxicities on human dermis fibroblast. The cytotoxic effect of compound 8d was more significant on PC3, MCF-7 and SKBr3 cancer cells with low-micromolar IC₅₀ value ranging from 0.11 to 0.59 μM, superior to Adriamycin drug. Mechanistic experimental and theoretical studies demonstrated that compounds 8d act as a K⁺ channel inhibitor in cancer models. Further molecular docking studies suggest that the EGFR Tyrosine Kinase enzyme may be a potential target for the most active 3-aryl-6-(N-methylpiperazin)-1,2,4-triazolo[3,4-a]phthalazines.

Experimental and theoretical study on the cyclic(alkyl)(amino)carbene-copper catalyzed Friedel-Crafts reaction of N,N-dialkylanilines with styrenes

The Friedel-Crafts reaction of alkalinous substrates is challenging because of the coordination between amines and traditional acid catalysts. Based on theoretical research, we designed a catalytic process for the Friedel-Crafts reactions of N,N-dialkylanilines in the presence of CAAC-CuCl [CAAC = cyclic(alkyl)(amino)carbene] and KB(C₆F₅)₄. Experimental results show that the catalytic system is suitable for a series of N,N-dialkylanilines and styrenes with good to excellent yields of para-selectivity products. The results are comparable to those obtained in carbene-gold catalyzed processes.

Optimization of phthalazin-based aryl/heteroarylhydrazones to design new promising antileishmanicidal agents: synthesis and biological evaluation of 3-aryl-6-piperazin-1,2,4-triazolo[3,4-a]phthalazines

1-Monosubstituted and 1,4-substituted phthalazins based on aryl/heteroarylhydrazinyl have demonstrated attractive antileishmanial profiles against amastigote forms of the Leishmania braziliensis parasite.

Cross-dehydrogenative regioselective Csp3–Csp2coupling of enamino-ketones followed by rearrangement: an amazing formation route to acridine-1,8-dione derivatives

A novel route for the construction of acridine-1,8-dione derivatives through CDC coupling of enamino-ketones followed by rearrangement.

Synthesis of fused oxazole-containing coumarin derivatives via oxidative cross coupling reaction using a combination of CuCl2 and TBHP

Various fused oxazoles containing coumarin derivatives were synthesized via an oxidative cross coupling reaction by employing 20 mol% CuCl₂ as the catalyst and TBHP as an oxidant.

Enantioselective oxidative functionalization of the Csp3–H bond adjacent to a nitrogen atom for rapid access to β-hydroxyl-α-amino acid derivatives

Highly chemoselective and enantioselective one-pot reactions involved in the oxidative functionalization of C_sp3–H bonds adjacent to nitrogen atoms were developed to rapidly construct highly functionalized β-hydroxyl-α-amino acid derivatives from simple starting materials under mild conditions.

Iminoiodane- and Brønsted base-mediated cross dehydrogenative coupling of cyclic ethers with 1,3-dicarbonyl compounds

A one-pot, two-step approach to prepare 2-tetrahydrofuran and -pyran substituted 1,3-dicarbonyl compounds by PhI=NTs-mediated amination/Brønsted base-catalyzed cross dehydrogenative coupling (CDC) reaction of the cyclic ether and 1,3-dicarbonyl derivative under mild conditions is reported. The reaction is compatible with a variety of cyclic ethers and 1,3-dicarbonyl compounds, affording the corresponding coupled products in moderate to good yields of up to 80% over two steps.

Friedel–Crafts reaction of indoles with vicinal tricarbonyl compounds generated in situ from 1,3-dicarbonyl compounds and TEMPO: highly selective synthesis of tertiary alcohols

A novel Friedel–Crafts reaction of indoles with vicinal tricarbonyl compounds generated in situ has been developed, forming indolyl tertiary alcohols. The process involves disproportionation of TEMPO, α-oxyamination, N–O bond cleavage and, finally, addition of the indole.

An I2-catalyzed oxidative cyclization for the synthesis of indolizines from aromatic/aliphatic olefins and α-picoline derivatives

A novel I₂-catalyzed intermolecular oxidative tandem cyclization reaction of aromatic/aliphatic olefins and α-picoline derivatives has been achieved for the synthesis of indolizines under metal-free conditions.

Iron-catalyzed aerobic C–H functionalization of pyrrolones

The aerobic oxidation of pyrrolones catalyzed by Fe(OTf)₃ to form reactive N-acyliminium ion intermediates that undergo nucleophilic additions to give the corresponding products is described.

C3 functionalization of indolizines via In(iii)-catalyzed three-component reaction

Post-functionalization at the C3 position of indolizines via In(iii)-catalyzed three-component coupling reaction with amines and aldehydes allowed rapid access to a new class of indolizines with diverse functional groups at the C3 position in good to excellent yields.

Oxidative cross coupling reaction mediated by I2/H2O2: a novel approach for the construction of fused thiazole containing coumarin derivatives

Various 2-phenyl-4H-chromeno(3,4-d)thiazol-4-one derivatives have been synthesized through C–H bond activation using sodium sulfide as a source of sulfur atoms and by employing I₂ as a catalyst and H₂O₂ as the terminal oxidant.

α-Vinylation of amides with arylacetylenes: synthesis of allylamines under metal-free conditions

A novel methodology for the α-vinylation of amides with arylacetylenes under metal-free conditions has been introduced. This methodology provides a new protocol to synthesize allylamines. In each product, the amount of the cis-isomer was more than that of the trans-isomer.

Copper-catalyzed acyloxylation of the C(sp3)–H bond adjacent to an oxygen by a cross-dehydrogenative coupling approach

We demonstrated a dehydrogenative cross coupling between a benzyl alcohol and C(sp³)–H bond for the construction of a C–O bond. This method reveals a new strategy for the direct use of benzyl alcohols in the synthesis of esters with the use of copper as a catalyst and TBHP as an oxidant.

Base-promoted dehydrogenative coupling of benzene derivatives with amides or ethers

Electronically neutral and deficient benzene derivatives are introduced into the dehydrogenative coupling as arenes that couple with amides/ethers.

Nickel or phenanthroline mediated intramolecular arylation of sp3 C-H bonds using aryl halides

The development of the intramolecular arylation of sp(3) C-H bonds adjacent to nitrogen using aryl halides is described. Arylation was accomplished using either Ni(COD)2 or 1,10-phenanthroline in substoichiometric amounts, and the reaction conditions were applied to a variety of electronically differentiated benzamide substrates. Preliminary studies suggest a mechanism involving aryl and alkyl radical intermediates.