Copper-catalyzed Oxidative Coupling Research Articles

Copper-Catalyzed Aerobic Oxidative Dehydrogenative Coupling to Access Benzo[c]cinnolines.

In this paper, a highly efficient copper-catalyzed oxidative dehydrogenative coupling to obtain benzo[c]cinnolines (up to 100% yield) was developed. It was found that DMAP was a highly efficient ligand for copper-catalyzed oxidation, and molecular oxygen was a green oxidizing agent. In this simple process, various functional groups were tolerated under mild reaction conditions, and the practicality of the process was demonstrated by the preparation of benzo[c]cinnolines on a gram scale and later derivatization.

Chiral α-Aminophosphonates as Ligands in Copper-Catalyzed Asymmetric Oxidative Coupling of 2-Naphthols.

Chiral α-aminophosphonates with adjacent carbon and phosphonate stereogenic centers have been employed as ligands in the copper-catalyzed oxidative coupling of 2-naphthols, resulting in the production of chiral BINOLs in favorable yields and moderate to good enantiomeric excess. This represents the first application of chiral P-based ligands to enable such a transformation. The synthesis of these chiral α-aminophosphonate ligands offers a significant advantage over approaches that typically necessitate elaborate synthetic processes for chiral ligand production.

Synthesis and Biological Activities of Scleropentaside D.

We report the first total synthesis of scleropentaside D, a unique C-glycosidic ellagitannin, from the ketal derivative of scleropentaside A employing site-selective O4-protection of C-acyl glycoside and copper-catalyzed oxidative coupling reaction of galloyl groups as the key steps. Our study confirms the proposed structure of this natural product, scleropentaside D, and demonstrates its effectiveness as an inhibitor of α-glycosidase.

Divergent Bimetallic Mechanisms in Copper(II)-Mediated C-C, N-N, and O-O Oxidative Coupling Reactions.

Copper-catalyzed aerobic oxidative coupling of diaryl imines provides a route for conversion of ammonia to hydrazine. The present study uses experimental and density functional theory computational methods to investigate the mechanism of N-N bond formation, and the data support a mechanism involving bimolecular coupling of Cu-coordinated iminyl radicals. Computational analysis is extended to CuII-mediated C-C, N-N, and O-O coupling reactions involved in the formation of cyanogen (NC-CN) from HCN, 1,3-butadiyne from ethyne (i.e., Glaser coupling), hydrazine from ammonia, and hydrogen peroxide from water. The results reveal two different mechanistic pathways. Heteroatom ligands with an uncoordinated lone pair (iminyl, NH2, OH) undergo charge transfer to CuII, generating ligand-centered radicals that undergo facile bimolecular radical-radical coupling. Ligands lacking a lone pair (CN and CCH) form bridged binuclear diamond-core structures that undergo C-C coupling. This mechanistic bifurcation is rationalized by analysis of spin densities in key intermediates and transition states, as well as multiconfigurational calculations. Radical-radical coupling is especially favorable for N-N coupling owing to energetically favorable charge transfer in the intermediate and thermodynamically favorable product formation.

Copper-catalyzed room-temperature cross-dehydrogenative coupling of secondary amides with terminal alkynes: a chemoselective synthesis of ynamides.

A copper-catalyzed aerobic oxidative cross-dehydrogenative coupling reaction between secondary amides and terminal alkynes has been developed. With the aid of ligands and 3 Å molecular sieves, ynamides can be efficiently synthesized at room temperature and conveniently scaled up. A legitimate mechanism involving nitrogen-centred radicals and copper trivalent intermediates has been proposed.

Green imine synthesis from amines using transition metal and micellar catalysis.

Imines are a versatile class of chemicals with applications in pharmaceuticals and as synthetic intermediates. While imines are conventionally synthesized via aldehyde-amine condensation, their direct preparation from amines can avoid the need for the independent preparation of the aldehyde coupling partner and associated constraints with regard to aldehyde storage and purification. The direct preparation of imines from amines typically utilizes transition metal catalysis and is often well-aligned with green chemistry principles. This review provides a comprehensive overview of transition metal catalysed imine synthesis, with a particular focus on the copper-catalyzed oxidative coupling of amines. The emerging application of micellar catalysis for imine synthesis is also surveyed due to its potential to avoid the use of hazardous solvents and intensify these reactions through reduced catalyst loadings and locally increased reactant concentrations. Future directions relating to the confluence of these two areas are proposed towards the more sustainable preparation of imines.

Synthesis of Sulfoximines by Copper-Catalyzed Oxidative Coupling of Sulfinamides and Aryl Boronic Acids.

A novel copper-catalyzed cross-coupling reaction of sulfinamides and aryl boronic acids is developed. The reaction is highly chemoselective and stereospecific, which allows mild synthesis of optically pure sulfoximines with broad scope and functional group tolerance. The utility of this method is demonstrated by the asymmetric synthesis of pharmaceutical intermediates.

Copper-catalyzed oxidative cross-dehydrogenative coupling (CDC) reaction of alcohols with secondary phosphine oxides

A copper-catalyzed oxidative cross-dehydrogenative coupling (CDC) strategy of secondary phosphine oxides and alcohols for the synthesis of various phosphinate esters was proposed. Under the mild reaction conditions (CuCl2·2H2O/K2S2O8, at room temperature for 3–12 h under air), a variety of substrates were well-tolerated and afforded the desirable compounds in moderate to excellent yields.

Copper-Catalyzed Phosphorylation of N,N-Disubstituted Hydrazines: Synthesis of Multisubstituted Phosphorylhydrazides as Potential Anticancer Agents.

An efficient copper-catalyzed aerobic oxidative cross-dehydrogenative coupling reaction for the synthesis of multisubstituted phosphorylhydrazides from N,N-disubstituted hydrazines and hydrogen phosphoryl compounds is accomplished. The reaction proceeds under mild conditions without the addition of any external oxidants and bases. This work reported here represents a direct P(═O)-N-N bond formation with the advantages of being operationally simple, good functional group tolerance, and high atom and step economy. Furthermore, the selected compounds exhibit potential inhibitory activity against tumor cells, which can be used in the field of screening of anticancer agents as new chemical entities.

Copper-Catalyzed Oxidative Coupling of Quinazoline-3-Oxides: Synthesis of O-Quinazolinic Carbamates.

Organic carbamates represent a kind of privileged structures in both organic chemistry and industry. Despite the fact that the synthesis of alcohol-based carbamates has been well studied, an efficient access to hydroxamic acid-based carbamates is less explored due to the nucleophilicity of both O and N atoms in hydroxamic acids. Herein, we report a copper-catalyzed oxidative coupling of quinazoline-3-oxides and formamides for the synthesis of O-quinazolinic carbamates. This protocol is featured with practicability, simple starting materials, and operational simplicity.

Novel Axially Chiral Ligand-Enabled Copper-Catalyzed Asymmetric Oxidative Coupling of 2-Naphthols for the Synthesis of 6,6'-Disubstituted BINOLs.

Novel axially chiral ligands have been designed and synthesized by merging the chelating picolinic acid with substituted BINOLs. The in-situ-prepared copper catalysts from the ligands and CuI enable the asymmetric oxidative coupling of 2-naphthols, affording 6,6'-disubstituted BINOLs in up to 89% yield with good enantioselectivities (up to 96:4 e.r.).

Copper-catalyzed enantioselective alkene carboetherification for the synthesis of saturated six-membered cyclic ethers.

The enantioselective copper-catalyzed oxidative coupling of alkenols with styrenes for the construction of dihydropyrans, isochromans, pyrans and morpholines is reported. A concise formal synthesis of a σ1 receptor ligand using this alkene carboetherification methodology was demonstrated. Ligand, solvent and base all impact reaction efficiency. DFT transition state calculations are presented.

Cu-Catalyzed Oxidative Thioesterification of Aroylhydrazides with Disulfides.

An alternative thioesterification reaction via copper-catalyzed oxidative coupling of readily available aroylhydrazides with disulfides is developed, in which oxidative expulsion of N2 overcomes the activation barrier between the carboxylic acid derivatives and the products. The reaction produces various thioesters in good to excellent yields with good functional group tolerance. In the reaction, stable and easily available aroylhydrazides are used as acyl sources and the relatively odorless disulfides are used as S sources. Mechanistic investigations demonstrate that the reaction of copper salt and oxidant (NH4)2S2O8 allows for achievement of tandem processes, including deprotonation, free-radical-mediated denitrogenation, and C-S bond formation.

Mechanistic insights into copper-catalyzed aerobic oxidative coupling of N–N bonds

Catalytic N–N coupling is a valuable transformation for chemical synthesis and energy conversion. Here, mechanistic studies are presented for two related copper-catalyzed oxidative aerobic N–N coupling reactions, one involving the synthesis of a pharmaceutically relevant triazole and the other relevant to the oxidative conversion of ammonia to hydrazine. Analysis of catalytic and stoichiometric N–N coupling reactions support an “oxidase”-type catalytic mechanism with two redox half-reactions: (1) aerobic oxidation of a CuI catalyst and (2) CuII-promoted N–N coupling. Both reactions feature turnover-limiting oxidation of CuI by O2, and this step is inhibited by the N–H substrate(s). The results highlight the unexpected facility of the N–N coupling step and establish a foundation for development of improved catalysts for these transformations.

Copper-catalyzed aerobic oxidative coupling of terminal alkynes with α-carbonyl aldehydes: An expedient approach toward ynediones

An efficient and mild one-pot approach for copper-catalyzed aerobic oxidative coupling of α-carbonyl aldehydes with terminal alkynes toward ynediones has been developed. Moreover, a variety of ynediones were constructed under the optimized reaction conditions, and a plausible mechanism was presented based on a series of control experiments.

Copper-Catalyzed Aerobic Oxidative Coupling of Aromatic Sulfonyl Hydrazides with Amines:A New Access to Aromatic Sulfonamides

Copper-Catalyzed Aerobic Oxidative Coupling of Aromatic Sulfonyl Hydrazides with Amines:A New Access to Aromatic Sulfonamides

Copper-Catalyzed Oxidative Coupling of AIBN and Ketone-Derived Enoxysilanes to γ-Ketonitriles.

A new and efficient oxidative coupling reaction between enoxysilane and alkylnitrile radicals derived from readily available AIBN and its analogues has been developed by using redox-active metal as a catalyst in which the redox-active copper is used for enhancing the electrophilicity of a free radical via coordination and bringing the radical and nucleophilic enol ether closer to facilitate the single-electron transfer. The present catalytic protocol afforded a variety of γ-ketonitriles in good to excellent yields with good functional group tolerance.

Regioselective Copper-Catalyzed Oxidative Coupling of α-Alkylated Styrenes with Tertiary Alkyl Radicals.

A radical-mediated oxidative cross-coupling of readily accessible α-alkylated styrenes with 1,3-dicarbonyl compounds utilizing a combination of Cu(OAc)2 and air as a catalytic system is described. Rather than requiring α-halocarbonyl compounds, this efficient approach enables direct installation of tertiary functionalized alkyl motifs to olefins with simple carbonyl derivatives. The novel protocol is characterized with high allylic selectivities via a competing β-H elimination. Both radical-clock and -trapping experiments provided clear-cut evidence for the intermediacy of an α-keto carbon-centered radical.

Copper-catalyzed oxidative coupling of quinoxalin-2(1H)-ones with alcohols: access to hydroxyalkylation of quinoxalin-2(1H)-ones

An efficient protocol for the synthesis of hydroxyl-containing quinoxalin-2(1H)-ones has been developed via the copper-catalyzed cross-coupling reaction of quinoxalin-2(1H)-ones with alcohols with moderate to good yields.

Copper-catalyzed oxidative coupling of arylboronic acids with aryl carboxylic acids: Cu3(BTC)2 MOF as a sustainable catalyst to access aryl esters

A straightforward and sustainable methodology for the synthesis of commercially important aryl esters via a C–O cross-coupling reaction was demonstrated using the Cu3(BTC)2 metal–organic framework.