423 research outputs found
4,5,12,13-Tetrabromo[2.2]paracyclophane - A New Bis(aryne) Equivalent
The reaction of 2 with nBuLi at -78°C generates aryne intermediates within the aromatic rings of [2.2]paracyclophane which are trapped in Diels-Alder reactions with dienes like furan, 1,9-diphenylisobenzofuran, or cyclopentadiene. Reductive deoxygenation with low-valent titanium reagents or TMSI converts the adducts of furan and isobenzofuran into anti-[2.2]paracyclophanes 4 and 5, respectively. The reaction of two aryne intermediates with [2.2](2,5)furanophane (7) yields 8 with three [2.2]paracyclophane units arranged in a stair-like fashion; yet, in this compound the highly shielded oxygen atoms cannot be removed anymore by reduction
Photocatalytic Synthesis of Polycyclic Indolones
In this work, a photocatalytic strategy for a rapid and modular access to polycyclic indolones starting from readily available indoles is reported. This strategy relies on the use of redox-active esters in combination with an iridium-based photocatalyst under visible-light irradiation. The generation of alkyl radicals through decarboxylative single electron reductions enables intramolecular homolytic aromatic substitutions with a pending indole moiety to afford pyrrolo- and pyridoindolone derivatives under mild conditions. Furthermore, it was demonstrated that these radicals could also be engaged into cascades consisting of an intermolecular Giese-type addition followed by an intramolecular homolytic aromatic substitution to rapidly assemble valuable azepinoindolones
[2.2](4,7)Isobenzofuranophanes - Synthesis, Characterisation and Reactivity
The isomeric Diels-Alder adducts 3, obtained by cycloaddition of tetraphenylcyclopentadienone to the 4,5:12,13-bis-(oxanorbornadieno)[2.2]paracyclophanes syn,syn- and anti,-syn-2[Note ][The stereochemical descriptors syn and anti refer to the orientation of the oxygen bridge in the oxabicyclo[2.2.1]heptadiene subunits with respect to the [2.2]paracyclophaneskeleton.], yield the unstable isobenzofuranophane 4 by consecutive extrusion of carbon monoxide and tetraphenylbenzene when heated to 180°C. The molecular ion of 4 was observed in the EI mass spectrum. The stable tetraphenyl-substituted analogue 10 was synthesized independently from the previously unknown 4,5,12,13-tetrabenzoyl[2.2]paracyclophane (9). UV/Vis as well as fluorescence spectra and an X-ray crystal structure analysis of 9 are reported
Synthetic Photoelectrochemistry
Photoredox catalysis (PRC) and synthetic organic electrochemistry (SOE) are often considered competing technologies in organic synthesis. Their fusion has been largely overlooked. We review state-of-the-art synthetic organic photoelectrochemistry, grouping examples into three categories: 1) electrochemically mediated photoredox catalysis (e-PRC), 2) decoupled photoelectrochemistry (dPEC), and 3) interfacial photoelectrochemistry (iPEC). Such synergies prove beneficial not only for synthetic "greenness" and chemical selectivity, but also in the accumulation of energy for accessing super-oxidizing or -reducing single electron transfer (SET) agents. Opportunities and challenges in this emerging and exciting field are discussed
6-Methyl-2-nitro-1-phenyl-hept-4-en-3-ol
In this short note, we report the synthesis of 6-methyl-2-nitro-1-phenyl-hept-4-en-3-ol by a LiAlH4 catalyzed nitroaldol reaction for carbon-carbon bond formation. The title compound was characterized by 1H-NMR, 13C-NMR, MS, IR and elemental analysis
Visible‐Light‐Driven Thiol‐yne Reaction: A Practical Synthesis of (1,2‐diarylvinyl)(aryl/alkyl)sulfides
A mild, efficient and straightforward visible-light-driven method has been developed to construct 1,2-diarylvinyl sulfides under catalyst- and additive-free conditions. The formation of small amounts of thiyl radicals under visible light irradiation allows the synthesis of 1,2-diarylvinyl sulfides in good yield with an excellent functional group tolerance
Photochemical Functionalization of Helicenes
Herein, a visible-light photochemical approach for practical helicene functionalization at very mild reaction conditions is described. The photochemical reactions allow for the regiospecific and innate late-stage functionalization of helicenes and are easily executed either through the activation of C(sp(2))-Br bonds in helicenes using K2CO3 as inorganic base or direct C(sp(2))-H helicene bond functionalization under oxidative photoredox reaction conditions. Overall, using these transformations six different functional groups are introduced to the helicene scaffold through C-C and four different C-heteroatom bond-forming reactions
Activated carbon as catalyst support: precursors, preparation, modification and characterization
The preparation of activated carbon materials is discussed along selected examples of precursor materials, of available production and modification methods and possible characterization techniques. We evaluate the preparation methods for activated carbon materials with respect to its use as catalyst support and identify important parameters for metal loading. The considered carbon sources include coal, wood, agricultural wastes or biomass as well as ionic liquids, deep eutectic solvents or precursor solutions. The preparation of the activated carbon usually involves pre-treatment steps followed by physical or chemical activation and application dependent modification. In addition, highly porous materials can also be produced by salt templating or ultrasonic spray pyrolysis as well as by microwave irradiation. The resulting activated carbon materials are characterized by a variety of techniques such as SEM, FTIR, nitrogen adsorption, Boehm titrations, adsorption of phenol, methylene blue and iodine, TPD, CHNS/O elemental analysis, EDX, XPS, XRD and TGA
N‑Arylation of NH-Sulfoximines via Dual Nickel Photocatalysis
The pharmaceutically underexplored sulfoximine moiety has emerged as a potentially active pharmaceutical ingredient. We developed a scalable synthetic route to N-arylated sulfoximines from the respective "free" NH-sulfoximines and bromoarenes. Our strategy is based on a dual nickel photocatalytic approach, is applicable for a broad scope of substrates, and exhibits a highly functional group tolerance. In addition, we could demonstrate that other sulfoximidoyl derivatives like sulfonimidamides and sulfinamides proceed smoothly under the developed reaction conditions
Visible‐Light‐Mediated Photoredox‐Catalyzed N‐Arylation of NH‐Sulfoximines with Electron‐Rich Arenes
The direct C-H/N-H dehydrogenative cross-coupling of NH-sulfoximines with electron-rich arenes was realized by oxidative visible-light photoredox catalysis, applying 9-mesityl-10-methylacridinium perchlorate as an organic photocatalyst. Sulfoximines display diverse desirable properties for medicinal chemistry and the pharmaceutical industry. However, their preparation is still challenging. Our reaction proceeds without sacrificial oxidant, at room temperature and is highly selective for the C-N bond forming reaction. The scope of the reaction includes mono- and multi-alkylated and halogenated arenes, which are reacted with aromatic and aliphatic electron-rich and electron-poor NH-sulfoximines, giving moderate to excellent yields of the N-arylated sulfoximines. In addition, we successfully conducted the developed reaction on a gram scale (1.5 g). Mechanistic investigations show that both arene and NH-sulfoximine interact with the excited-state of the photocatalyst. We propose a radical-based mechanism, where both the arene and the NH-sulfoximine are photo-oxidized to their respective radical intermediates. Radical-radical cross-coupling subsequently leads to the N-arylated sulfoximine. Two electrons and two protons are released during the reaction and are subsequently converted into H-2 by a proton-reducing cobalt-catalyst
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