Refernces
10.1016/j.tetlet.2012.07.093
The study describes a new and efficient method for synthesizing indolo[3,2,1-jk]carbazoles through palladium-catalyzed intramolecular cyclization of N-(2-bromoaryl)carbazoles. The reaction involves forming carbon-carbon bonds via intramolecular arylation, which proceeds with the cleavage of C–X and C–H bonds on the carbazole ring. Various substituted N-aryl carbazole substrates, containing both electron-donating and electron-withdrawing groups, were explored under optimized conditions. The study successfully yielded indolo[3,2,1-jk]carbazoles with high thermostability, good fluorescence properties, and electron-donor potential, making them promising candidates for applications in organic electronics and material chemistry.
10.1039/c8cc07481j
The research focuses on the development of a Pd(II)-catalyzed cross-coupling protocol for the b-C(sp3)–H activation/cross-coupling of aliphatic acid derivatives containing a-hydrogen atoms with aryltrifluoroborates. The study addresses the challenge of C(sp3)–H bond functionalization, particularly in substrates with a-hydrogen atoms, which typically suffer from issues like b-hydride elimination and slow C–H cleavage rates. The researchers engineered a weak, bidentate directing group to enhance the rate of C–H cleavage and facilitate transmetallation. The experiments involved the use of palladium acetate (Pd(OAc)2) as the catalyst, N-Ac-Ile-OH as the ligand, silver carbonate (Ag2CO3), and 1,4-benzoquinone as an additive, among other reagents, to optimize the reaction conditions and evaluate the method's potential for asymmetric b-C(sp3)–H arylation. The analyses included monitoring the reaction yields using 1H NMR spectroscopy with CH2Br2 as an internal standard and evaluating the electronic properties and steric hindrance of various directing groups to assess their influence on reactivity. The study successfully demonstrated the arylation of aliphatic acid derivatives with a range of aryltrifluoroborates, offering a promising approach for the synthesis of enantioenriched aliphatic acid derivatives.
10.1021/ic701144y
The research focuses on the selective cyclopalladation of iminophosphoranes, specifically R3PdNCH2Aryl compounds, through experimental and computational studies. The reactants include various iminophosphoranes with different substituents at the phosphorus and aryl rings, such as 1a to 1g, which are palladated with Pd(OAc)2 or Pd2(dba)3. The experiments involve the palladation of these iminophosphoranes, leading to the formation of orthopalladated complexes, which are characterized as either endo or exo isomers based on the position of the palladium atom relative to the ligand. The analyses used to determine the structure and properties of the resulting complexes include IR and NMR spectroscopy, which provide insights into the bonding and geometry of the complexes. Computational studies using DFT methods were also employed to understand the reaction mechanisms and to explain the kinetic and thermodynamic preferences for endo versus exo palladation, as well as the influence of solvent and temperature on the reaction selectivity.
10.1002/ejic.200800007
The study focuses on the synthesis, characterization, and catalytic application of palladacycles containing phosphane or phosphane oxide functionalities. These palladacycles are designed to serve as highly active catalysts in palladium-catalyzed cross-coupling reactions, specifically the Suzuki and Heck reactions. The key chemicals used in the study include ligand precursors PhN=C(CMe2)(NPh)C=N(CH2)2PPh2 (1) and PhN=C(CMe2)(NPh)C=N(CH2)2P(O)Ph2 (2), which were treated with Pd(OAc)2 to form palladium(II) complexes 3 and 4. Additional reactions with LiCl led to the formation of complex 5. These complexes were then applied to catalyze the Suzuki and Heck reactions with aryl halide substrates, demonstrating their potential as effective catalysts in these important organic synthesis processes. The study also investigates the catalytic activity of these palladacycles and compares their performance with other palladacycles, providing insights into the influence of electronic and steric properties of the ligands on the catalytic cycle.
10.1021/acs.orglett.6b01132
The research focuses on the palladium-catalyzed cross-coupling reaction between allylboronic acids and α-diazoketones, which selectively forms linear allylic products with the creation of a new C(sp3)?C(sp3) bond. The study was conducted without an external oxidant, suggesting that the Pd-catalyst does not undergo redox reactions during the process. The reaction conditions were optimized to achieve promising yields, with Pd(II) catalysts such as Pd(TFA)2 and Pd(OAc)2 proving more efficient in CH2Cl2 as the solvent. The addition of catalytic amounts of CuI was found to significantly improve the yield. The study also explored the synthetic scope of the reaction, demonstrating that various α-diazoketones with different aromatic substituents could participate in the cross-coupling with allylboronic acids, leading to the formation of linear allylic products with a new C(sp3)?C(sp3) bond. The reaction's regioselectivity was found to be opposite in Cu- and Pd-catalyzed reactions, and the Pd-catalyst was likely preserved in its +2 oxidation state throughout the reaction, expanding the synthetic scope of transition metal-catalyzed cross-coupling reactions suitable for C(sp3)?C(sp3) bond formation.
10.1021/jacs.8b09186
The study presents a protocol for synthesizing chiral spiroheterocyclic and benzofused heterocyclic compounds through a Pd-catalyzed enantioselective intramolecular dearomative Heck reaction. The reaction involves the cross-coupling of aryl halides or aryl triflates with the internal C=C bonds of indoles, benzofurans, pyrroles, and furans. The protocol utilizes various chiral phosphoramidite ligands, such as new BINOL- and H8-BINOL-based ligands, and (S)-SEGPHOS, which play crucial roles in achieving high enantioselectivities. The reactions are performed in the presence of palladium catalysts (Pd(OAc)? or Pd(dba)?) and bases like Cs?CO? or NEt?, with formic acid (HCO?H) often added to enhance enantioselectivity. The study demonstrates a broad substrate scope, yielding products with good to excellent yields and enantioselectivities. The synthesized compounds feature N/O-substituted quaternary carbon stereocenters and exocyclic olefin moieties, and further synthetic transformations of these products, such as hydrogenation, hydroboration, and ring-expanding rearrangements, are also explored without loss of enantiopurity.
10.1016/S0040-4039(00)85262-4
The study presents a novel and selective method for the deoxygenation of phenols through the reduction of aryl triflates. The key chemicals involved are aryl triflates, which are the substrates to be reduced; triethylammonium formate, which acts as the hydrogen donor; and a homogeneous palladium catalyst, typically palladium acetate, which facilitates the reaction. Triethylamine is also used as a base, and phosphine ligands, such as triphenylphosphine or 1,1'-bis(diphenylphosphino)ferrocene (DPPF), are employed to stabilize the palladium catalyst and enhance its activity. The reaction is carried out in DMF solvent, with formic acid added to generate the active hydrogen donor species. The study demonstrates that this method is highly chemoselective, tolerating various functional groups like nitro, ketones, esters, and olefins, and it provides high yields of aromatic hydrocarbons. The mechanism likely involves oxidative addition of the aryl triflate to the palladium catalyst, displacement of the triflate by formate ion, loss of carbon dioxide to form an arylpalladium(II) hydride, and subsequent reductive elimination to yield the aromatic hydrocarbon and regenerate the active palladium species.
10.3762/bjoc.9.240
The research presents a mild, efficient, and ligand-free method for the direct arylation of 5-pyrazolones using Pd-catalyzed C–H bond activation. The study focuses on the synthesis of 4-aryl-5-pyrazolones, which are significant heterocyclic compounds used in medicinal and biological research. The experiments involved the reaction of 5-pyrazolones with aryl halides using Pd(OAc)2 as a catalyst, with optimization of reaction conditions including the use of different bases, catalysts, solvents, and reaction temperatures. The results were analyzed in terms of product yield, and the optimal conditions were identified as using 0.1 equiv Pd(OAc)2 catalyst, 2.0 equiv Ag2CO3, acetonitrile solvent, 90 °C, air atmosphere, a 1:2 molar ratio of 5-pyrazolone to aryl halide, and a reaction time of 12 hours. The scope of the reaction was also tested with various aryl halides and 5-pyrazolone substrates, showing moderate to excellent yields. The research was supported by several foundations and the characterization data for all compounds is provided in the supporting information.
10.1021/jm0401098
The research focuses on the development of pyrroloquinolone PDE5 inhibitors with enhanced pharmaceutical properties for the treatment of erectile dysfunction (ED). The team at Johnson & Johnson Pharmaceutical Research and Development designed a series of analogues to address the low aqueous solubility and poor oral bioavailability of initial lead compounds. They employed two main strategies: increasing overall basicity and reducing molecular weight. The synthesis involved reactions such as Winterfeldt oxidation of α-carboline precursors and coupling reactions with pyrroloquinolone precursors. Various reactants, including chloropyrimidines, bromopyridines, and stannanylpyridines, were used in conjunction with catalysts like Pd(OAc)2 and BINAP for cross-coupling reactions. The synthesized compounds were analyzed for their potency against PDE5, selectivity against other PDE isozymes, oral bioavailability in rats, dogs, and monkeys, and their ability to elevate intracellular cGMP levels in RFL-6 cells. The in vivo efficacy was also evaluated in canine models. The study successfully identified lead compounds, such as 11e and 11l, which showed improved bioavailability and efficacy, marking significant progress towards clinical candidates for ED treatment.
10.1021/ja962313t
The research discusses the nature of the catalytic palladium-mediated elimination of allylic carbonates and acetates to form 1,3-dienes, a significant synthetic transformation in organic chemistry. The study aimed to understand the details of this reaction, particularly the regioselectivity and isotope effects observed with different substrates. The researchers used a variety of chemicals, including palladium catalysts such as Pd(OAc)2 and PBu3, as well as isotopically labeled derivatives like 13C-labeled and deuterated compounds. They concluded that the reaction proceeds with a preference for the loss of hydrogen over deuterium, indicating a more linear C-H(D) bond cleavage transition state, and that the elimination of certain cyclic allylic carbonates occurs via a stereospecific anti-elimination pathway, which is inconsistent with the commonly accepted β-hydride elimination mechanism. Instead, the results support a mechanism involving stereospecific anti-addition of LnPd(0) to the allylic carbonate followed by base-promoted anti-elimination. The study was financially supported by the National Institutes of Health and involved the synthesis and elimination of various allylic carbonates, including the cyclic allylic carbonate 14, to test the proposed mechanisms.
10.1016/j.poly.2008.11.038
The study investigates the kinetics of complex formation between palladium(II) acetate and 1,1’-bis(diphenylphosphino)ferrocene (dppf) in CDCl3 and DMSO-d6 solvents using 31P NMR spectroscopy. Palladium(II) acetate acts as the metal source, while dppf serves as the ligand. In CDCl3, the reaction directly forms the [Pd(dppf)(OAc)2] species with dppf acting as a chelate ligand. In DMSO-d6, an intermediate is initially formed, which then converts into the more stable [Pd(dppf)(OAc)2] species. The rate constants for these reactions were determined through computer fitting of integration-time data, revealing that complex formation is faster in CDCl3 than in DMSO-d6, likely due to DMSO's coordinating ability, which slows the coordination of dppf and decreases the electrophilicity of the metal center.
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