10.1002/anie.201004593
The study presents an innovative approach to C-C bond formation through NHC-catalyzed Michael addition to α,β-unsaturated aldehydes, utilizing redox activation. The researchers, Suman De Sarkar and Armido Studer, explore the use of N-heterocyclic carbenes (NHCs) to activate α,β-unsaturated aldehydes, which then react with various 1,3-dicarbonyl compounds to form dihydropyranones. They demonstrate that this method is effective with different nucleophiles and enals, achieving high yields and selectivity under mild conditions. The process involves a two-step umpolung reaction at the β-position of the α,β-unsaturated aldehyde, followed by a redox-type activation. The study also includes control experiments to rule out alternative mechanisms, such as kinetic O-acylation, and provides a proposed catalytic cycle for the process. This work contributes to the field of organocatalysis by offering a new strategy for conjugate addition reactions using soft C-nucleophiles and showcases the potential of NHCs in redox activation.
10.1021/ol800115p
The research described in the article focuses on the synthesis of chiral 3,3'-bipyrroles, which are significant for their presence in natural products and potential applications in conducting polymers and pharmaceuticals. The experiments involved a Lewis acid-catalyzed one-pot, three-component route using diaroyl acetylene and 1,3-dicarbonyls as reactants, with ammonium acetate serving as the nitrogen source. The reaction was optimized using various Lewis acid catalysts, with In(OTf)3 and InCl3 proving most effective, and isopropyl alcohol (IPA) as the preferred solvent. The axial chirality of the bipyrroles was confirmed through X-ray crystal structure analysis and Density Functional Theory (DFT) calculations. The absolute configuration of the enantiomers was determined by comparing theoretical CD spectra calculations using the ZINDO method with experimental CD spectra obtained after separating the racemates on a chiral column. The research also explored the atropisomerism of bipyrroles and their potential applications, suggesting further studies for their use as chiral ligands and in electrochemical sensing.
10.1021/acscatal.9b01535
The research focuses on the development of a novel and cost-effective asymmetric transfer hydrogenation (ATH) catalyst system using ruthenium (Ru) complexes with minimal stereogenicity. The study introduces a series of Ru-catalysts, denoted as B1-B12, which feature a single stereogenic element derived from (1-pyridine-2-yl)methanamine ligands. These catalysts were designed to simplify existing protocols and demonstrate high levels of stereoinduction across a broad range of ketone substrates, including those challenging for known catalyst systems. The experiments involved the use of achiral diphosphines and (1-(pyridine-2-yl)methanamine derivatives as reactants, with 2'-chloroacetophenone as a model substrate. The catalysts were evaluated under mild transfer hydrogenation conditions using isopropanol (iPrOH) as the hydrogen source and potassium tert-butoxide (BuOK) as the base. The performance of each catalyst was analyzed in terms of yield and enantioselectivity (ee), with catalyst B10 showing the highest enantioselectivity of up to 91% ee. The study also explored the synthetic utility of the new catalysis protocol in a three-step preparation of a chiral (1-(pyridine-2-yl)methanamine ligand in its enantio-pure form, highlighting the economic and efficiency advantages over traditional methods.
10.1021/jo00113a011
The research presents a comprehensive study on the synthesis and photochemistry of 5,7-bis(diazo)-1,2,3,4-dibenzocyclohepta-1,3-dien-6-one, a 1,3-bis(diazo) ketone incorporated into a seven-membered ring. The primary objective was to investigate the photochemical pathways of this compound, which was achieved through product analysis and matrix isolation spectroscopy. The study concluded that the compound's photochemistry is significantly different from its five-membered ring analog, as it eliminates two diazo groups to produce cyclopropenone, leading to phenanthryne upon further irradiation in a low-temperature matrix. In contrast, in solution, the first diazo group cleavage generates a diazo ketene intermediate that undergoes self-condensation or reacts with nucleophiles. Key chemicals used in the process include the title compound 15, various alcohols (methanol, ethanol, and 2-propanol), diethylamine, benzene, acetonitrile, dichloromethane, and furan, among others.
10.1021/j100350a029
The study investigates the sonochemistry of argon-saturated water-alcohol mixtures using ESR and spin trapping with 3,5-dibromo-4-nitrosobenzenesulfonate (DBNBS). It examines free-radical intermediates induced by 50-kHz ultrasound in aqueous solutions of ethanol, 1-propanol, 2-propanol, and 2-methyl-2-propanol. The chemicals involved include various alcohols (ethanol, 1-propanol, 2-propanol, 2-methyl-2-propanol, methanol), water (H2O), deuterated water (D2O), and DBNBS as the spin trap. The alcohols serve as the primary solutes under investigation, while water and deuterated water act as solvents and provide isotopic labeling for tracking reactions. DBNBS is crucial for capturing and identifying radicals formed during sonolysis through its spin adducts. The study identifies spin adducts typical of thermal decomposition of the alcohols and of H- and OH-induced abstraction reactions, observes isotopically mixed radicals in mixed-isotope systems, and examines the effects of solvent composition and temperature on the sonochemical yields of radicals.
10.1016/S0040-4020(01)87766-8
The research investigates the behavior of gem-cyano-ethoxycarbonyl compounds (la-c and 7) when treated with sodium borohydride (NaBH4) and lithium aluminium hydride (LiAlH4). The purpose is to explore the reduction reactions of these compounds and understand the resulting products and their conformations. The study found that treating la-c with NaBH4 in solvents like 2-propanol or PEG-400 led to the reduction of the ethoxycarbonyl group and reductive deacetylation, yielding compounds 2a-c and 3a-b. When la-c and 7 were treated with NaBH4-CoCl2, selective reduction of the cyano group to an aminomethyl group occurred, with an acetyl group migrating to the aminomethyl group. Reduction with LiAlH4 followed by acetylation produced gem-aminomethyl-hydroxymethyl compounds 6a-c and 11. The study concluded that the preferred conformations of the resulting compounds depend on the spatial arrangement of the acetoxy groups, with compounds like 4a-b, 5a-b, and 6a-b showing equatorial disposition, while others like 4c, 5c, and 6c preferred axial disposition. The findings provide insights into the reactivity and structural preferences of these compounds under different reducing conditions.
10.1021/ol060045q
The study presents a Pd/C-catalyzed method for the deoxygenation of phenolic hydroxyl groups in phenol derivatives, converting them into aryl triflates or mesylates using magnesium metal in methanol (MeOH) at room temperature. The key innovation is the use of ammonium acetate (NH4OAc) as an additive, which significantly enhances the reaction's reactivity and rate. This approach is environmentally friendly, widely applicable, and operates under mild conditions without the need for a phosphine ligand or hydrogen gas. The method is effective for a variety of aryl triflates and mesylates, offering a practical and efficient route for deoxygenation in synthetic organic chemistry. The researchers also explored the reaction mechanism, suggesting that it involves an initial single electron transfer (SET) from magnesium to the palladium-activated aromatic ring, leading to the formation of an anion radical that subsequently eliminates the (trifluoro)methane sulfonic anion to produce the reduced arene product.
10.1016/j.tet.2011.03.045
The research focuses on the nucleophilic ring-opening reactions of 1-aralkyl-3,4-epoxypiperidines with various aliphatic and aromatic amines. The main objective was to develop a short-step synthesis method for 4-fluorobenzyltrozamicol and novel anilidopiperidines with high regiocontrol. The study utilized different solvents, including protic solvents like 2-propanol and acetonitrile, with and without the assistance of metal salts such as LiBr and LiClO4 to achieve high regioselectivity in the formation of 3-amino-piperidin-4-ols and 4-amino-piperidin-3-ols. The experiments involved the synthesis of 1-aralkyl-3,4-epoxypiperidines, their ring-opening with amines, and subsequent transformations to form the desired compounds. The research also explored the steric effects on regioselectivity and provided structural correlations through NMR analysis. The products were characterized using techniques such as HPLC, NMR, and mass spectrometry, with detailed analyses of the ratios of regioisomers and the yields of the synthesized compounds.
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