Nitroepoxides as Versatile Precursors to 1,4-Diamino Heterocycles

Catalyst free one pot three components synthesis of 2-iminothiazoles from nitroepoxides and thiourea

Nitroepoxides were introduced as efficient substrates for the one-pot three-component synthesis of 2-iminothiazoles under catalyst-free conditions. Reaction of amines, isothiocyanates, and nitroepoxides in THF at 10-15 °C afforded corresponding 2-iminothiazoles in high to excellent yields. The reaction proceeds via the in situ formation of thiourea from an amine and an isothiocyanate, followed by nitroepoxide ring opening with the sulfur of thiourea, cyclization reaction, and dehydration cascade. The structures of products were confirmed by IR, NMR, HRMS analyses and X-ray crystallography.

Base-catalyzed multicomponent access to quinoxalin-2-thiones from o-phenylenediamines, aryl ketones and sulfur

3-Arylquinoxaline-2-thiones were conveniently synthesized via three-component oxidative condensation of acetophenones with o-phenylenediamines and sulfur in DMSO in the presence of piperidine as a catalyst. The products could be readily isolated from the reaction mixture by simple precipitation and washing with methanol. This set of reaction conditions applied to higher homologs of acetophenones as well as benzyl phenyl ketones led to 2,3-di-C-substituted quinoxalines. Further functionalization of 3-phenylquinoxaline-2-thione via reaction on the thione group could be readily performed to provide quinoxaline derivatives in good yields.

tert-Butyl Hydroperoxide Promoted the Reaction of Quinazoline-3-oxides with Primary Amines Affording Quinazolin-4(3H)-ones

An efficient and facile approach for the synthesis of quinazolin-4(3H)-ones via the reaction of quinazoline-3-oxides with primary amines is described. This approach is demonstrated to be applicable for a broad range of substrates and proceeds efficiently under metal-free and mild reaction conditions employing easily available tert-butyl hydroperoxide as the oxidant. Remarkably, 3-(2-(1H-indol-3-yl) ethyl)quinazolin-4(3H)-one 3w, which was conveniently obtained by this process in 70% yield, was an excellent precursor for the synthesis of bioactive evodiamine and rutaempine.

Tetrabutylammonium Bromide-Catalyzed Transfer Hydrogenation of Quinoxaline with HBpin as a Hydrogen Source

A metal-free environmentally benign, simple, and efficient transfer hydrogenation process of quinoxaline has been developed using the HBpin reagent as a hydrogen source. This reaction is compatible with a variety of quinoxalines offering the desired tetrahydroquinoxalines in moderate-to-excellent yields with Bu₄NBr as a noncorrosive and low-cost catalyst.

Iron-catalyzed one-pot synthesis of quinoxalines: transfer hydrogenative condensation of 2-nitroanilines with vicinal diols

Here, we report iron-catalyzed one-pot synthesis of quinoxalines via transfer hydrogenative condensation of 2-nitroanilines with vicinal diols. The tricarbonyl (η4-cyclopentadienone) iron complex, which is well known as the Knölker complex, catalyzed the oxidation of alcohols and the reduction of nitroarenes, and the corresponding carbonyl and 1,2-diaminobenzene intermediates were generated in situ. Trimethylamine N-oxide was used to activate the iron complex. Various unsymmetrical and symmetrical vicinal diols were applied for transfer hydrogenation, resulting in quinoxaline derivatives in 49–98% yields. A plausible mechanism was proposed based on a series of control experiments. The major advantages of this protocol are that no external redox reagents or additional base is needed and that water is liberated as the sole byproduct.

A transfer hydrogenative condensation between 2-nitroanilines and vicinal diols for the synthesis of quinoxalines, with no additional oxidant, reductant and base.

Catalyst-Free Synthesis of Benzofuran Derivatives from Cascade Reactions between Nitroepoxides and Salicylaldehydes

Different benzofuran derivatives are synthesized via a catalyst-free reaction between nitroepoxides and salicylaldehydes. In the employed methodology, K₂CO₃ and DMF have been used at 110 °C, and the reactions were completed after 12 h in 33-84% yields. The highest yields were obtained using 3-nitrosalicylaldehyde. Finally, a plausible mechanism was proposed for the reaction, and some evidence was provided for this mechanism such as the detection of released acetate anion (using FTIR) and isolation and structure determination of the critical intermediate.

NaOH-Mediated Direct Synthesis of Quinoxalines from o-Nitroanilines and Alcohols via a Hydrogen-Transfer Strategy

A NaOH-mediated sustainable synthesis of functionalized quinoxalines is disclosed via redox condensation of o-nitroamines with diols and α-hydroxy ketones. Under optimized conditions, various o-nitroamines and alcohols are well tolerated to generate the desired products in 44-99% yields without transition metals and external redox additives.

Recent advances in the synthesis and reactivity of quinoxaline

Quinoxalines are observed in several bioactive molecules and have been widely employed in designing molecules for DSSC's, optoelectronics, and sensing applications. Therefore, developing newer synthetic routes as well as novel ways for their functionalization is apparent.

Transition Metal-Free Heteroarylation of Quinoxaline: Construction of Heteroaryl-Fused Phenazines by Oxidative Coupling

A concise method for the construction of heteroaryl-fused phenazines was developed via PIFA-BF₃·Et₂O-mediated oxidative coupling of di-heteroarylated quinoxalines for the first time. Synthesis of mono- and di-heteroarylation of quinoxaline was performed effectively using only LiTMP reagent under transition metal-free conditions and without the use of halogen-containing starting compounds. In addition, nonsymmetrical di-heteroarylated quinoxalines were synthesized through reheteroarylation of mono-heteroarylated quinoxalines in the same way. Oxidation of the saturated compounds formed after heteroarylation was easily accomplished with iodine. The UV-vis absorption and fluorescence features of some compounds were examined.

Unravelling the mechanism of the organocatalyzed aminolytic kinetic resolution of α-nitroepoxides: a theoretical study

The mechanism of the aminolytic kinetic resolution of 2-methyl-2-nitro-3-phenyl oxirane with aniline in the presence of Takemoto's catalyst is disclosed by way of DFT calculations.

Nitroepoxide ring opening with thionucleophiles in water: synthesis of α-xanthyl ketones, β-keto sulfones and β-keto sulfonic acids

Nitroepoxide ring opening with thionucleophiles such as potassium xanthates, sodium aryl sulfinates and sodium bisulfite in water is investigated to provide the corresponding α-xanthyl-α-aryl-2-propanones, β-keto sulfones and β-keto sulfonic acids.

NH2OH-HCl-Mediated Umpolung α-Methylsulfonylation of α-Sulfonyl Ketones with Methylsulfoxides: Synthesis of α,β-Bis-sulfonyl Arylketones

In this paper, a novel and efficient route for the synthesis of α,β-bis-sulfonyl arylketones via an NH₂OH-HCl-mediated intermolecular umpolung α-methylsulfonylation of α-sulfonyl ketones with methylsulfoxides is described. A plausible mechanism is proposed and discussed. Various reaction conditions for this efficient, one-pot, environmentally friendly transformation were investigated.

Three-Step Telescoped Synthesis of Monosubstituted Vicinal Diamines from Aldehydes

Aldehydes are easily transformed into vicinal diamines and piperazines through a one-pot procedure including a Darzens reaction and treatment with an amine or diamine and then with a reducing agent. Additionally, quinoxalines can be accessed by reaction with 1,2-benzenediamine under oxidative conditions. These transformations are simple methods for the preparation of synthetically interesting monosubstituted diamines, piperazines, and quinoxalines.

Regioselective Opening of Nitroepoxides with Unsymmetrical Diamines

Nitroepoxides are easily transformed into benzodiazepines, tetrahydrobenzodiazepines, imidazopyridines, and N-alkyl tetrahydroquinoxalines by treatment with 2-aminobenzylamines, 2-aminopyridines, and N-alkyl 1,2-diaminobenzenes, respectively. Regioselectivity is controlled through attack of the most nucleophilic nitrogen of the unsymmetrical diamine to the β position of the epoxide. These reactions represent an efficient way to prepare privileged bioactive structures.

A multi-component synthesis of N-substituted 2-amino-3-cyano pyrroles via ring-opening of nitroepoxides

A multi-component synthesis of N-substituted 2-amino-3-cyano pyrroles from nitroepoxides, amines and malononitrile has been demonstrated.

Synthesis of N,S-Heterocycles and Dithiocarbamates by the Reaction of Dithiocarbamic Acids and S-Alkyl Dithiocarbamates with Nitroepoxides

A facile and efficient procedure for the synthesis of substituted thiazole-2(3H)-thiones and thiazolidine-2-thiones by the reaction of primary amines, carbon disulfide, and nitroepoxides is described. By using secondary amines in this protocol, the corresponding dithiocarbamate-substituted phenyl-2-propanones were prepared in excellent yields. In addition, substituted thiazoles and 1-(alkylthio)-1-phenylpropan-2-ones were prepared in reactions of S-alkyl dithiocarbamates and nitroepoxides.

Synthesis of substituted pyrazines from N-allyl malonamides

Synthesis of highly substituted pyrazines from geminal diazides via thermal or copper-mediated cyclization and modification of the obtained pyrazines.

Palladium-Catalyzed Modular Synthesis of Substituted Piperazines and Related Nitrogen Heterocycles

We report here a novel method for the modular synthesis of highly substituted piperazines and related bis-nitrogen heterocycles via a palladium-catalyzed cyclization reaction. The process couples two of the carbons of a propargyl unit with various diamine components to provide nitrogen heterocycles in generally good to excellent yields and high regio- and stereochemical control.

Catalytic enantioselective epoxidation of nitroalkenes

Nitroepoxides are potentially exploitable as synthons with vicinal electrophilic centers.

Highly efficient and eco-friendly protocol to functionalized imidazoles via ring-opening of α-nitro epoxides

A simple and direct synthesis of functionalized imidazoles from α-nitro-epoxides and amidines was developed.

Catalytic enantioselective synthesis of α-nitroepoxides via aminolytic kinetic resolution

The first enantioselective synthesis of β-aryl-substituted α-nitroepoxides, exploiting an organocatalyzed aminolytic kinetic resolution (AKR), has been developed.