3010-81-9Relevant academic research and scientific papers
Synthesis, crystal structure, and luminescence of tetrakis(4-methoxyphenyl) methane
Guieu, Samuel,Rocha, Jo?o,Silva, Artur M.S.
, p. 2870 - 2873 (2013)
A new synthesis of a tetrahedral tecton, tetrakis(4-methoxyphenyl)methane, is reported. This compound exhibits a strong fluorescence around 340 nm at room temperature, both in solution and in the solid state. Upon crystallization, another luminescence band can be observed around 500 nm, attributed to phosphorescence. A study of the single-crystal structure of the compound provided a rationalization of this crystallization induced phosphorescence. The crystal of tetrakis(4-methoxyphenyl)methane belongs to the tetragonal space group P4?21c, and the structural analysis revealed a close packing of the molecules, with no void space and no solvent molecules in the crystal. The molecules are held together in a columnar array via multiple C-Ha?π hydrogen bonds. The hydrogen bonds between the molecules impede the torsional vibrations of the aromatic rings, preventing thermal relaxation from the triplet state, and hence promoting phosphorescence at room temperature.
Shuttle arylation by Rh(I) catalyzed reversible carbon–carbon bond activation of unstrained alcohols
Lutz, Marius D.R.,Gasser, Valentina C.M.,Morandi, Bill
supporting information, p. 1108 - 1119 (2021/04/19)
The advent of transfer hydrogenation and borrowing hydrogen reactions paved the way to manipulate simple alcohols in previously unthinkable manners and circumvented the need for hydrogen gas. Analogously, transfer hydrocarbylation could greatly increase the versatility of tertiary alcohols. However, this reaction remains unexplored because of the challenges associated with the catalytic cleavage of unactivated C–C bonds. Herein, we report a rhodium(I)-catalyzed shuttle arylation cleaving the C(sp2)–C(sp3) bond in unstrained triaryl alcohols via a redox-neutral β-carbon elimination mechanism. A selective transfer hydrocarbylation of substituted (hetero)aryl groups from tertiary alcohols to ketones was realized, employing benign alcohols as latent C-nucleophiles. All preliminary mechanistic experiments support a reversible β-carbon elimination/migratory insertion mechanism. In a broader context, this novel reactivity offers a new platform for the manipulation of tertiary alcohols in catalysis.
Temperature-Dependent Reactivity of a Non-heme FeIII(OH)(SR) Complex: Relevance to Isopenicillin N Synthase
Yadav, Vishal,Siegler, Maxime A.,Goldberg, David P.
supporting information, p. 46 - 52 (2021/01/13)
Non-heme iron complexes with cis-FeIII(OH)(SAr/OAr) coordination were isolated and examined for their reactivity with a tertiary carbon radical. The sulfur-ligated complex shows a temperature dependence on ?OH versus ArS? transfer, whereas the oxygen-ligated complex does not. These results provide the first working model for C-S bond formation in isopenicillin N synthase and indicate that kinetic control may be a key factor in the selectivity of non-heme iron "rebound"processes.
Determining the Inherent Selectivity for Carbon Radical Hydroxylation versus Halogenation with FeIII(OH)(X) Complexes: Relevance to the Rebound Step in Non-heme Iron Halogenases
Yadav, Vishal,Rodriguez, Rodolfo J.,Siegler, Maxime A.,Goldberg, David P.
supporting information, p. 7259 - 7264 (2020/04/22)
The first structural models of the proposed cis-FeIII(OH)(halide) intermediate in the non-heme iron halogenases were synthesized and examined for their inherent reactivity with tertiary carbon radicals. Selective hydroxylation occurs for these cis-FeIII(OH)(X) (X = Cl, Br) complexes in a radical rebound-like process. In contrast, a cis-FeIII(Cl)2 complex reacts with carbon radicals to give halogenation. These results are discussed in terms of the inherent reactivity of the analogous rebound intermediate in both enzymes and related catalysts.
Dioxygen-Derived Nonheme Mononuclear FeIII(OH) Complex and Its Reactivity with Carbon Radicals
Yadav, Vishal,Gordon, Jesse B.,Siegler, Maxime A.,Goldberg, David P.
supporting information, p. 10148 - 10153 (2019/07/05)
A new tetradentate, monoanionic, mixed N/O donor ligand (BNPAPh2O-) with second coordination sphere H-bonding groups has been synthesized for stabilization of a terminal FeIII(OH) complex. The complex FeII(BNPAPh2O)(OTf) (1) reacts with O2 to give a mononuclear terminal FeIII(OH) complex, FeIII(OH)(BNPAPh2O)(OTf) (2), both of which were characterized by X-ray diffraction, electrospray ionization mass spectrometry, UV-vis, 1H and 19F nuclear magnetic resonance, 57Fe M?ssbauer, and electron paramagnetic resonance spectroscopies. Treatment of 2 with carbon radicals (Ar3C·) gives Ar3COH and the FeII complex 1, in direct analogy with the elusive radical "rebound" process proposed for nonheme iron enzymes.
Synthesis and biological evaluation of novel N-substituted nipecotic acid derivatives with an alkyne spacer as GABA uptake inhibitors
Tóth, Krisztián,H?fner, Georg,Wanner, Klaus T.
, p. 3668 - 3687 (2018/06/19)
In this study, we present the synthesis and structure–activity relationships (SAR) of novel N-substituted nipecotic acid derivatives closely related to (S)-SNAP-5114 (2) in the pursuit of finding new and potent mGAT4 selective inhibitors. By the use of iminium ion chemistry, a series of new N-substituted nipecotic acid derivatives containing a variety of heterocycles, and an alkyne spacer were synthesized. Biological evaluation of the prepared compounds showed, how the inhibitory potency and subtype selectivity for the murine GABA transporters (mGATs) were influenced by the performed modifications.
Synthesis of ketones via organolithium addition to acid chlorides using continuous flow chemistry
Moon, Soo-Yeon,Jung, Seo-Hee,Bin Kim,Kim, Won-Suk
, p. 79385 - 79390 (2015/10/06)
An efficient method for the synthesis of ketones using organolithium and acid chlorides under continuous flow conditions has been developed. In contrast to standard batch chemistry, over-addition of the organolithium to the ketone for the formation of the undesired tertiary alcohol has been minimised representing a direct approach toward ketones.
Acid-catalysed hydrolysis of trityl derivatives in strongly acidic aqueous media
Canle L., Moises,Maskill, Howard
supporting information, p. 1016 - 1022 (2014/01/06)
The kinetics of hydrolysis (deamination or dealcoholation) of tritylamines and 2,2,2-trifluoroethyl ethers and their corresponding 4-methoxy, 4,4′-dimethoxy-, and 4,4′,4″-trimethoxy-substituted analogues in aqueous solutions up to 3.5 mol · dm-3 in strong acid have been investigated at constant ionic strength. In all cases, acid-catalysed hydrolytic processes have been observed, with finite reactivity at [H 3O+] = 0. Strong upward curvature has been observed for kobs versus [HClO4]. Analysis of this dependence in terms of the HR acidity function and the X0 excess acidity scale allow explanation of the observed behaviour in terms of the increasing differences between concentrations and activities of the various species involved in the processes, including water, for which the activity coefficient strongly diverges from its standard state value as the acidity increases. This analysis has shown that, by taking account of the effect of the ionic strength, the same mechanistic models proposed for mildly acidic solutions are valid in more highly concentrated acid media. These comprise (i) protonation of the trityl ether followed by C-O bond heterolysis to give a carbenium ion-alcohol (ion-molecule) pair which can separate, and (ii) C-N bond heterolysis of the protonated tritylamine to give a carbenium ion-amine (ion-molecule) pair followed by separation of the fragments or protonation of the amine and subsequent separation of the ions. Each separated (substituted) trityl carbenium ion, regardless of its provenance, is invariably captured by a solvent molecule (water). Copyright 2013 John Wiley & Sons, Ltd. Strong upward curvatures observed for kobs versus [H3O+] kinetics results in the hydrolysis of tritylamines and trityl ethers in strongly acidic aqueous solutions are entirely understandable as medium effects and accurately described in terms of excess acidities. The mechanisms previously proposed for mild acidic conditions have been generalized to more strong acid media. Copyright
Electrophilicity versus electrofugality of tritylium ions in aqueous acetonitrile
Horn, Markus,Mayr, Herbert
supporting information; scheme or table, p. 7478 - 7487 (2010/08/20)
First-order rate constants kw for the reactions of a series of donorsubstituted triphenylmethylium (tritylium) ions with water in aqueous acetonitrile have been determined photometrically at 20°C using stopped-flow and laser-flash techniques. T
Stabilities of trityl-protected substrates: The wide mechanistic spectrum of trityl ester hydrolyses
Horn, Markus,Mayr, Herbert
supporting information; experimental part, p. 7469 - 7477 (2010/09/11)
Ionization rates of para-substituted triphenylmethyl (trityl) acetates, benzoates, and para-nitrobenzoates have been determined in aqueous acetonitrile and aqueous acetone at 25 °C. Conventional and stoppedflow techniques have been used to evaluate rate constants ranging from 1.38 × 10-5 to 2.15 × 102S-1 by conductimetry and photospectrometry methods. The varying stabilities of the differently substituted tritylium ions account for a gradual change of reaction mechanism. Poorly stabilized carbocations are generated slowly by the ionization of their covalent precursors and trapped fast by water. Better stabilized carbocations are generated more rapidly and accumulate, so that ionization and trapping by water can be observed as separate steps in a single experiment. Finally, highly stabilized tritylium ions do not react with water, and only the rates of their formation could be measured. The ionization rate constants correlate linearly with Winstein's ionizing powers Y; the low slopes (0.17 + parameters is excellent for symmetrically substituted tritylium derivatives, deviations for unsymmetrically substituted systems are observed. The failing rate-equilibrium relationship between the rates of ionizations (log kion) and the stabilities of the carbocations in aqueous solution (pKR+) may be explained by the late " development of resonance between a p-amino group and the carbocationic center of the tritylium ion during the ionization process.
