- Tris(4-methoxyphenyl)methanol
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Tris(4-methoxyphenyl)methanol, C22H22O4, crystallizes in space group P21 with two molecules in the asymmetric unit. The molecules are linked into dimers by a weak O-H...O hydrogen bond [O...O 3.035 (3) A].
- Ferguson, George,Glidewell, Christopher,Patterson, Iain L. J.
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- Novel PTM-TEMPO biradical for fast dissolution dynamic nuclear polarization
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The synthesis and characterization of a novel trityl-TEMPO biradical and the investigation of its properties as Dynamic Nuclear Polarization (DNP) polarizing agent are reported. Comparison with a structurally related monoradical (PTM-TEMPE) or mixtures of
- Muoz-Gmez, Jose-Luis,Marn-Montesinos, Ildefonso,Lloveras, Vega,Pons, Miquel,Vidal-Gancedo, Jos,Veciana, Jaume
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- Electrochemical and Spectroscopic Studies on Triarylamine-Polychlorotriphenylmethyl Dyads with Particularly Strong Triarylamine Donors
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We present two new donor-acceptor dyads composed of a polychlorotriphenylmethyl radical (PTM.) as the acceptor (A) and bis(4-dimethylaminophenyl)(phenyl)amine (TPAN) or 2,2’:6’,2’’:6’’,6-trioxytriphenylamine (TOTA) as particularly electron-rich triarylamine (TAA) donors (D). We assessed their electrochemical properties and electronic structures by cyclic voltammetry, UV/vis/NIR spectroscopy, EPR spectroscopy and quantum chemical calculations. By establishing the spectroscopic fingerprints of the oxidized and reduced forms, we probe for the possible coexistence of a zwitterionic TAA+-PTM? valence tautomer (VT), besides neutral TAA-PTM.. UV/vis/NIR and EPR spectroscopic studies at variable temperature and in various solvents however provide no indication for such equilibria. Quantitative spin counting experiments by EPR spectroscopy and quantum chemical calculations indicate that the one-electron oxidized forms of these dyads possess an open-shell singlet ground state which is energetically slightly below the triplet state.
- Breimaier, Stefanie,Winter, Rainer F.
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p. 4690 - 4700
(2021/09/10)
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- Expeditious and practical synthesis of tertiary alcohols from esters enabled by highly polarized organometallic compounds under aerobic conditions in Deep Eutectic Solvents or bulk water
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An efficient protocol was developed for the synthesis of tertiary alcohols via nucleophilic addition of organometallic compounds of s-block elements (Grignard and organolithium reagents) to esters performed in the biodegradable choline chloride/urea eutectic mixture or in water. This approach displays a broad substrate scope, with the addition reaction proceeding quickly (20 s reaction time) and cleanly, at ambient temperature and under air, straightforwardly furnishing the expected tertiary alcohols in yields of up to 98%. The practicability of the method is exemplified by the sustainable synthesis of some representative S-trityl-L-cysteine derivatives, which are a potent class of Eg5 inhibitors, also via telescoped one-pot processes.
- Quivelli, Andrea F.,D'Addato, Giovanna,Vitale, Paola,García-álvarez, Joaquín,Perna, Filippo M.,Capriati, Vito
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- Exploration of mechanochemical activation in solid-state fluoro‐grignard reactions
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Owing to the strength of the C–F bond, the ‘direct’ preparation of Grignard reagents, i.e., the interaction of elemental magnesium with an organic halide, typically in an ethereal solvent, fails for bulk magnesium and organofluorine compounds. Previously described mechanochemical methods for preparing Grignard reagents have involved ball milling powdered magnesium with organochlorines or bromines. Activation of the C–F bond through a similar route is also possible, however. For example, milling 1- and 2-fluoronaphthalene with an excess of magnesium metal for 2 h, followed by treatment with FeCl3 and additional milling, produces the corresponding binaphthalenes, albeit in low yields (ca. 20%). The yields are independent of the particular isomer involved and are also comparable to the yields from corresponding the bromonaphthalenes. These results may reflect similar charges that reside on the α-carbon in the naphthalenes, as indicated by density functional theory calculations.
- Hanusa, Timothy P.,Speight, Isaiah R.
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supporting information
(2020/02/06)
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- Redox-Active PTM Radical Dendrimers as Promising Multifunctional Molecular Switches
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Nowadays there is a great interest in using individual molecules as nanometer-scale switches and logic devices, with the aim of reaching higher power and smaller size. Demonstrating that one molecular switch can be turned on and off at room temperature si
- Lloveras, Vega,Liko, Flonja,Mu?oz-Gómez, José L.,Veciana, Jaume,Vidal-Gancedo, José
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p. 9400 - 9412
(2019/11/21)
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- An Efficient Ga(OTf)3/Isopropanol Catalytic System for Direct Reduction of Benzylic Alcohols
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This study aims to report the first gallium-catalyzed direct reduction of benzylic alcohols using isopropanol as a reductant. The reaction proceeds via gallium catalyst-assisted hydride transfer of the in situ-generated benzylic isopropyl ether. The method generates only water and acetone as byproducts and thus provides an atom-economic and environmentally friendly approach to the synthesis of di- and triarylmethanes, which are important substructures in various bioactive compounds and functional materials. (Figure presented.).
- Sai, Masahiro
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supporting information
p. 4330 - 4335
(2018/10/15)
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- Direct allylation of benzyl alcohols, diarylmethanols, and triarylmethanols mediated by XtalFluor-E
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We report the direct allylation of benzyl alcohols, diarylmethanols and triarylmethanols mediated by XtalFluor-E using allyltrimethylsilane. The resulting allylated products are obtained in moderate to high yield.
- Lebleu, Thomas,Paquin, Jean-Fran?ois
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supporting information
p. 442 - 444
(2017/01/10)
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- Optimized S-trityl-l-cysteine-based inhibitors of kinesin spindle protein with potent in vivo antitumor activity in lung cancer xenograft models
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The mitotic kinesin Eg5 is critical for the assembly of the mitotic spindle and is a promising chemotherapy target. Previously, we identified S-trityl-l-cysteine as a selective inhibitor of Eg5 and developed triphenylbutanamine analogues with improved pot
- Good, James A. D.,Wang, Fang,Rath, Oliver,Kaan, Hung Yi Kristal,Talapatra, Sandeep K.,Podgórski, Dawid,MacKay, Simon P.,Kozielski, Frank
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supporting information
p. 1878 - 1893
(2013/05/08)
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- Stabilities of trityl-protected substrates: The wide mechanistic spectrum of trityl ester hydrolyses
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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.
- Horn, Markus,Mayr, Herbert
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supporting information; experimental part
p. 7469 - 7477
(2010/09/11)
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- Electrophilicity versus electrofugality of tritylium ions in aqueous acetonitrile
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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
- Horn, Markus,Mayr, Herbert
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supporting information; scheme or table
p. 7478 - 7487
(2010/08/20)
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- Base-induced rearrangement of tritylamines to imines: discovery and investigation of the mechanism
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An unexpected compound, the aniline derived benzophenone imine, was isolated when tritylamine was treated with n-BuLi and alkyl halides, during the formation of N-alkyl tritylamines, in the process of preparing primary amines. A nucleophilic attack of the nitrogen anion of tritylamide on the adjacent C-bonded phenyl, either substituted or not, involving a bridging anionic intermediate, is proposed for this base-induced tritylamine rearrangement to produce the corresponding imine. Electron-withdrawing groups in the aromatic ring, favoring the negative charge development, affect the relative migratory tendencies.
- Theodorou, Vassiliki,Skobridis, Konstantinos,Karkatsoulis, Aris
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p. 4284 - 4289
(2007/10/03)
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- Cinchona alkaloid phase-transfer catalysts revisited: Influence of substituted aryl groups on the enantioselectivity of glycine ester enolate alkylation
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We report herein, the influence of substituted aryl groups in quaternary ammonium salts derived from cinchona alkaloids on enantioselectivity of the alkylation of glycine ester enolates.
- Kumar, Sanjeev,Ramachandran, Uma
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p. 7022 - 7028
(2007/10/03)
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- Palladium-catalyzed arylation of α,α-disubstituted arylmethanols via cleavage of a C-C or a C-H bond to give biaryls
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The palladium-catalyzed arylation of α,α-disubstituted arylmethanols with aryl halides proceeds not only via C-H bond cleavage at the ortho-position, but also via cleavage of the sp2-sp3 C-C bond with the liberation of ketones (β-carbon elimination) to give the corresponding biaryls. Both reactions appear to occur through common arylpalladium(II) alcoholate intermediates. The results of systematic studies with respect to which C-C or C-H bond is preferentially cleaved in the arylation are reported. Among the important findings is the selective elimination of ortho-substituted aryl groups even from aryl(diphenyl)methanols due to steric reasons. Thus, various biaryls having ortho-substituents can be produced efficiently by treatment of the corresponding aryl(diphenyl or dimethyl)methanols with aryl bromides and chlorides.
- Terao, Yoshito,Wakui, Hiroyuki,Nomoto, Michiyo,Satoh, Tetsuya,Miura, Masahiro,Nomura, Masakatsu
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p. 5236 - 5243
(2007/10/03)
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- Triarylmethanes and 9-arylxanthenes as prototypes amphihydric compounds for relating the stabilities of cations, anions and radicals by C-H bond cleavage and electron transfer
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Thermodynamic stability properties of 11 p-substituted trityl and seven 9-phenylxanthyl carbocations are reported in sulfolane and of their conjugate carbanions in DMSO. The cations are compared by calorimetric heats of hydride transfer from cyanoborohydride ion, their first and second reduction potentials, their pK+Rs in aqueous sulfuric acid, 13C chemical shifts and free energies of methoxy exchange. Carbanions are compared by their heats and free energies (pKHA) of deprotonation and their first and second oxidation potentials. Radicals are compared by their oxidation and reduction potentials. Their bond dissociation energies are derived by alternative routes: from the carbocation and its reduction potential and from the carbanion and its oxidation potential. The various properties are correlated against each other and against appropriate Hammett-type substituent parameters. Correlations between the different measured properties reported here range from fair to excellent. Despite their importance as historic prototypes for the three trivalent oxidation states of carbon, trityl and xanthyl systems are atypical models for comparing transmission of electron demand in other series of carbocations, radicals or carbanions with significantly different structures. The 9-arylxanthyl series is especially poor because of its insensitivity to substituent effects. The effects of substituents on various properties which represent the stabilities of R+s correlate surprisingly well against those for corresponding R-s. Accordingly, compensating effects on the oxidation and reduction of a series of related R.s may lead to a nearly constant electron transfer energy and absolute hardness for the series. In contrast, the free energies for interconversion of the carbocations and carbanions which determine the gap between pKR+. and pKHA are very sensitive to structural change.
- Arnett, Edward M.,Flowers II, Robert A.,Ludwig, Richard T.,Meekhof, Alison E.,Walek, Stuart A.
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p. 499 - 513
(2007/10/03)
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- Chemoselective Preparation of Ketones by the Grignard Reaction of N-Acylpyrazoles
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N-Acylpyrazoles afford chemoselectively the corresponding ketones in good yields by the use of equimolar amounts of Grignard reagent.In the case of an optically active N-acylpyrazole, optical asymmetry was retained in comparable optical yield.Ketone formation by the Grignard reactions can be regarded as an important functionalization in a synthetic loop using pyrazoles as the auxiliary compound.
- Kashima, Choji,Kita, Isanobu,Takahashi, Katsumi,Hosomi, Akira
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- RADICAL-ANIONS OF AROMATIC COMPOUNDS. XXII. THE EFFECT OF SUBSTITUENTS IN THE RADICAL-ANIONS OF BENZOPHENONE DERIVATIVES ON THE RATIO OF THE COMPETING PATHS AND ON THE COMPOSITION OF THE PRODUCTS FROM THE REACTION OF THEIR POTASSIUM SALTS WITH N,N,N-TRIMETHYLPHENYLAMMONIUM PERCHLORATE
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The reaction of the potassium salts of the radical-anions of ketones C6H5COC6H4X (where X = 4-CH3, 3-CH3, 3-CH3O, and 3-F) with N,N,N-trimethylphenylammonium perchlorate in tetrahydrofuran was studied.The ratio of the rates of the processes, including nucleophilic attack at the methyl group of the ammonium cation by the radical-anion (SN) and electron transfer from the radical-anion to the electrophile (ET), and also the ratio of the products corresponding to phenylation of the ketone (the precursor of the radical-anion) formed in the latter case hardly depend at all on the nature of the substituent X.In contrast, the yield of the products corresponding to C-methylation of the radical-anion in the SN process increases with increase both in the electron-donating and in the electron-withdrawing characteristics of the substituents X.
- Selivanov, B. A.,Bil'kis, I. I.,Shteingarts, V. D.
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p. 1357 - 1365
(2007/10/02)
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- A Kinetic Study of the Rearrangement of Triarylacetonitrile Oxides
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The thermal rearrangement of triphenylacetonitrile oxide (1a) to triphenylmethyl isocyanate (2) is a first-order process.Rate constants at five temperatures between 116 and 190 deg C were determined giving ΔH(excit.) = 9.3 +/- 1.1 kcal/mol and ΔS(excit.) = -58.2 +/- 2.4 cal/mol*K.The rearrangement of substituted triarylacetonitrile oxides (1b-d) occur only slightly faster than that of 1a.These results are interpreted in terms of a concerted single-step rearrangement in which the highly ordered transition state (6c) has a degree of radical character.
- Gibbs, Leslie W.,Wedegaertner, Donald K.
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p. 7320 - 7322
(2007/10/02)
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- Reactivities of triarylmethyl and diarylmethyl cations with azide ion investigated by laser flash photolysis. Diffusion-controlled reactions
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By use of the technique of laser flash photolysis, rate constants kAz and ks have been directly measured for the reactions at 20 °C in acetonitrile-water (AN-W) solutions of varying composition of 18 triarylmethyl and 10 diarylmethyl cations with azide and solvent. The cations have ks that depend on substituent and vary from ～101 to ～107 s-1. For the more stable ions kAz also varies, increasing with decreased electron donation and also increasing by as much as 103 with increasing acetonitrile content. For less stable cations, however, the rate constant becomes independent of substituent. The break occurs when ks has reached ～105 s-1. The limiting rate constants have magnitudes in the vicinity of 1010 M-1 s-1; these do depend on solvent and type of cation, with diarylmethyl cations reacting at the limit 1.6 ± 0.2 times faster than triarylmethyl. The data can be fit by a model where there is diffusional encounter of the cation and azide to form an ion pair, with the combination within the ion pair rate-limiting for the more stable cations and the diffusion step rate-limiting for the less stable ones. The limiting rate constants represent the latter, diffusional encounter of the cation and azide. The Debye-Smoluchowski equation for diffusion-controlled reactions predicts rate constants that are larger than observed by factors of 2-2.5 for diarylmethyl and 4 for triarylmethyl. Deviations can be attributed to nonproductive encounters where the anion has approached the cation in the plane of one of the rings and thus cannot form a proper reacting configuration. The difference between the two types of cations is explained by the greater difficulty of achieving this configuration with the more sterically congested triarylmethyl cation. Ratios kAz/ks obtained from product analysis (competition kinetics) have previously been found to show adherence to the reactivity-selectivity principle. This has been interpreted (Rappoport, Jencks) in terms of the reaction with azide having reached the diffusion limit. The directly measured kAz establish that this is indeed the case. This study also validates the use of azide as a "clock" (Jencks, Richard) for converting such ratios to absolute rate constants through use of a value of 5 × 109 M-1 s-1 for kAz. The directly measured diffusion-limited kAz are somewhat larger than this, but the differences are small, at most a factor of 4.
- McClelland, Robert A.,Kanagasabapathy,Banait, Narinder S.,Steenken, Steen
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p. 1009 - 1014
(2007/10/02)
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The use of 4-methoxytrityl (monomethoxytrityl, Mmt) and 4-methyl-trityl (Mtt) groups of N1m-protection of Fmoc-His is described. Both groups being unaffected by base, e.g. piperidine and diethylamine, can be quantitatively removed under very mi
- Barlos, Kleomenis,Chatzi, Olga,Gatos, Dimitrios,Stavropoulos, George,Tsegenidis, Theodore
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p. 475 - 478
(2007/10/02)
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- Phenylvinylogously Extended Triphenylmethylium Systems
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As isoconjugated models for (phenylazo)tritylium ions of type A the tritylium systems containing one to three styryl or phenylethynyl substituents have been investigated.In accordance with simple theoretical model considerations these ions have VIS absorptions at considerably longer wavelengths than tritylium ion itself.They also show the expected bathochromic band shifts in going from the singly branched (1, 4) to the doubly and triply branched systems 2, 3 and 5, 6 as well as the predicted bathochromic shifts for 4-methoxystyryl (1b-3b) and hypsochromic shifts for 4-( dimethylammoniostyryl)- and 4-(nitrostyryl)tritylium ions 1c-3c and 1d, respectively.For most of the newly prepared tritylium systems fully resolved NMR spectra were obtained, whose signal positions correlate very well with the charge distributions derived from the elementary conjugation model.For the 4,4'-(1,2-ethenediyl)bistritylium system 12, whose color resembles that of 4-styryltritylium ion 1a, only the resonance lines of the inner protons 3,β-H and carbons C-4,β show significant deviations from the corresponding signal positions of the reference systems 1a and tritylium (13). - Key Words: Chromophores, combined / Ethene, diphenyl- / Ethyne, diphenyl- / Phenylmethylium
- Hellwinkel, Dieter,Fritsch, Helmut
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p. 2351 - 2360
(2007/10/02)
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- Aroyl Anion Trapping Reactions. A Preliminary Study of Direct Nucleophilic Aroylation by Means of Low Temperature, in situ (CH3)nC6H5 nLi/CO Systems.
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Results of studies of the in situ nucleophilic aroylation of PhCO2Me, Me3CCO2Me and Ph2CO by several low temperature ArLi/CO systems (Ar = C6H5, p-CH3C6H4, o-CH3C6H4, 2,6-(CH3)2C6H3 and 2,4,6-(CH3)3C6H2) are reported.The experiments with C6H5Li were unsuccessfull and the best results were obtained with 2,6-(CH3)2-C6H3Li.
- Seyferth, Dietmar,Wang, Wei-Liang,Hui, Rihard C.
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p. 1651 - 1654
(2007/10/02)
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