RESUMO
A C(sp2)-C(sp2) bond can be constructed via a photoredox/N-heterocyclic carbene (NHC)-cocatalyzed radical cross-coupling reaction, which provides a complementary strategy to classic electron pair processes. The present protocol represents the first example of an NHC-catalyzed two-component radical cross-coupling reaction involving C(sp2)-centered radical species. The decarboxylative acylation of oxamic acid with acyl fluoride was conducted under mild conditions and allowed the preparation of a variety of useful α-keto amides, including sterically congested ones.
RESUMO
An N-heterocyclic carbene (NHC)-catalyzed strategy has been developed to address the issue of using toxic transitional metals in the field of C-C bond activation. The novel reaction mode enables an efficient docking between the cyanoalkyl from the cycloketone oxime derivative and the acyl group from the aldehyde, affording ketonitrile in moderate to good yields, which is one kind of useful building block for synthesizing nitrogen-containing pharmacophores.
RESUMO
We report a direct C-H aminoalkylation reaction using two light-activated H-atom transfer catalyst systems that enable the introduction of protected amines to native adamantane scaffolds with C-C bond formation. The scope of adamantane and imine reaction partners is broad and deprotection provides versatile amine and amino acid building blocks. Using readily available chiral imines, the enantioselective synthesis of the saxagliptin core and rimantadine derivatives is also described.
Assuntos
Aminas/química , Carbono/química , Hidrogênio/química , Luz , Alquilação , Aminoácidos/química , Catálise , Iminas/química , EstereoisomerismoRESUMO
A new general de novo synthesis of pharmaceutically important α-aryl ß-perfluoroalkyl ketones has been disclosed. Compared with trifluoromethylation-initiated radical 1,2-aryl migration of α,α-diaryl allylic alcohols, this protocol employs a new strategy of biomimetic carbene catalysis to assemble alkene, aldehyde and perfluoroalkyl reagents, providing access to products with excellent flexibility of the aryl unit and perfluoroalkyl group. This method also demonstrates excellent functional group compatibility, including some Grignard reagent sensitive groups.
RESUMO
Biological treatment played an important role in the treatment of landfill leachate. In the current study, acid mine drainage (AMD) was used as a source of sulfate to strengthen the anaerobic treatment of landfill leachate. Effects of chemical oxygen demand (COD) and SO42- mass concentration ratio on the decomposition of organic matter, methane production and sulfate reduction were investigated and the microbial community was analyzed using the high throughout methods. Results showed that high removal efficiency of COD, methane production and heavy metal removal was achieved when the initial COD/SO42- ratio (based on mass) was set at 3.0. The relative abundance of anaerobic hydrogen-producing bacteria (Candidatus Cloacamonas) in the experimental group with the addition of AMD was significantly increased compared to the control. Abundance of hydrogenotrophic methanogens of Methanosarcina and Methanomassiliicoccus was increased. Results confirmed that AMD could be used as sulfate resource to strengthen the biological treatment of landfill leachate.
Assuntos
Bactérias/metabolismo , Análise da Demanda Biológica de Oxigênio , Metais Pesados/isolamento & purificação , Metais Pesados/metabolismo , Metano/biossíntese , Mineração , Sulfatos/metabolismo , Reatores Biológicos/microbiologia , Precipitação Química , Concentração de Íons de Hidrogênio , Fatores de Tempo , Poluentes Químicos da Água/isolamento & purificação , Poluentes Químicos da Água/metabolismoRESUMO
A redox-economical strategy for the synthesis of trifluoromethylated enamides using copper catalysis is reported. The reaction employs the inexpensive Langlois reagent (CF3SO2Na) and takes place without the need of an external oxidant. The trifluoromethylated enamide products can easily be converted into the corresponding ketone, saturated amide or oxazole.
RESUMO
An iron-catalyzed coupling reaction of O-acyloximes and O-benzoyl amidoximes with silyl enol ethers is reported. The protocol provides access to functionalized pyrroles, 1,6-ketonitriles, pyrrolines and imidazolines via carbon-centered radicals generated from an initially formed iminyl radical. The intramolecular cyclization and ring-opening processes of the iminyl radical take place preferentially over reactions that proceed through a 1,3-hydrogen transfer, providing insights into iron-catalyzed reactions with oxime derivatives. The cheap and environmentally friendly iron catalyst, the broad substrate scope and the functional group compatibility make this protocol useful for synthesis of valuable nitrogen-containing products.
RESUMO
A novel intramolecular oxycyanation of methylenecyclopropanes is reported that proceeds through oxidative cleavage of the N-CN bond and subsequent palladium transfer from N to O of the amide group. A range of substituted benzo[d][1,3]oxazines with a cyano group are readily furnished by this newly developed oxycyanation reaction. Tris(4-trifluoromethylphenyl)phosphine as a ligand has been found to be crucial to effectively promote the transformation with high chemo- and regioselectivity. Moreover, the reaction outcome can be significantly affected by the electronic effect of the acyl group attached to the nitrogen atom of methylenecyclopropanes. When R(3) is a chloromethyl group, the pyrrolo[2,3-b]quinoline derivative is obtained by thermal-induced [3+2] cycloaddition of methylenecyclopropane to the methanediimine intermediate.
RESUMO
The chemoselective [4+2] vs. [2+2] cycloaddition between allenoates and dithioesters can be controlled by switching the nucleophilic amine catalyst. The two modes of cyclizations represent the first example of controllable and chemoselective annulations between allenoates and dienophiles catalyzed by amine. These cyclizations are useful in offering a divergent synthesis of sulfur-containing heterocycles. On the basis of this investigation, it can be realized that dithioesters with a vicinal electron-withdrawing group can react not only like a Michael acceptor but also as a ketone or imine.
RESUMO
Rh(II)-catalyzed intermolecular [3+2] cycloaddition of 2 H-azirines with N-sulfonyl-1,2,3-triazoles is disclosed, in which a series of fully functionalized pyrroles is produced via rhodium azavinyl carbene intermediates. A distinct feature of this reaction is that the azavinyl carbene serves as a [2 C] equivalent, instead of as [1 C] or aza-[3 C] synthons, which have been reported previously in cyclopropanations and [3+n] cycloadditions. Moreover, this methodology has also been successfully applied in the total synthesis of URB447 as well as the formal synthesis of Atorvastatin (Lipitor).
Assuntos
Atorvastatina/síntese química , Azirinas/química , Compostos de Benzil/síntese química , Pirróis/síntese química , Ródio/química , Triazóis/química , Atorvastatina/química , Compostos de Benzil/química , Catálise , Reação de Cicloadição , Pirróis/química , EstereoisomerismoRESUMO
The first example for the preparation of enantioenriched azo compounds from hydrazones and Morita-Baylis-Hillman adducts has been developed, affording azo compounds incorporating an oxindole scaffold in up to 91% yield along with a 93% ee value under the catalysis of (DHQ)2AQN.
Assuntos
Antraquinonas/química , Compostos Azo/síntese química , Éteres/química , Hidrazonas/química , Indóis/química , Isatina/química , Compostos Azo/química , Catálise , Estrutura Molecular , Oxindóis , EstereoisomerismoRESUMO
Yb(NTf(2))(3)-catalyzed [3 + 3] cycloaddition between isatin ketonitrones and cyclopropanes is described. A variety of spiro[tetrahydro-1,2-oxazine]oxindoles were obtained in moderate to good yields along with good regioselectivities. This is the first example of the intermolecular [3 + 3] cycloaddition between ketone-derived nitrones and cyclopropanes.
Assuntos
Ciclopropanos/química , Indóis/química , Isatina/química , Ácidos de Lewis/química , Óxidos de Nitrogênio/química , Oxazinas/química , Compostos de Espiro/química , Itérbio/química , Catálise , Ciclização , Reação de Cicloadição , Modelos Moleculares , Oxindóis , EstereoisomerismoRESUMO
OBJECTIVE: To evaluate the effect of K2O addition on the crystallization property of dental glass-ceramics in the Li2O-SiO2-Al2O3-P2O5-ZnO system. METHODS: Different content of K2O was added into Li2O-SiO2-Al2O3-P2O5-ZnO glass system. The heat-treated system of the glass-ceramics was determined by differential thermal analyses (DTA), then the crystallization components and the microstmcture of the glass-ceramics with different content of K2O were investigated from X-ray diffraction (XRD) analyses and scanning electron microscopy (SEM). RESULTS: Addition of K2O helped to reduce the viscosity of the glass system and improved crystallization. More lithium disilicate crystals appeared after heated-treatment of the glass system which contained 5.3 wt% addition of K2O, and the homogeneously lath-shaped crystals were 4 gm in length. CONCLUSION: Certain content of K2O can improve the crystallization property of dental glass-ceramics in the Li2O-SiO2-Al2O3-P2O5-ZnO system.