6266-56-4Relevant academic research and scientific papers
Kinetically Controlled, Highly Chemoselective Acylation of Functionalized Grignard Reagents with Amides by N?C Cleavage
Li, Guangchen,Szostak, Michal
supporting information, p. 611 - 615 (2020/01/02)
The direct transition-metal-free acylation of amides with functionalized Grignard reagents by highly chemoselective N?C cleavage under kinetic control has been accomplished. The method offers rapid and convergent access to functionalized biaryl ketones through transient tetrahedral intermediates. The direct access to functionalized Grignard reagents by in situ halogen–magnesium exchange promoted by the versatile turbo-Grignard reagent (iPrMgCl?LiCl) permits excellent substrate scope with respect to both the amide and Grignard coupling partners. These reactions enable facile, operationally simple and chemoselective access to tetrahedral intermediates from amides under significantly milder conditions than chelation-controlled intermediates. This novel direct two-component coupling sets the stage for using amides as acylating reagents in an alternative paradigm to the metal-chelated approach, acyl metals and Weinreb amides.
MELANIN PRODUCTION INHIBITOR
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Paragraph 0230 - 0233; 0263 - 0267, (2015/12/17)
Disclosed is a melanin production inhibitor which has an excellent inhibitory activity on the production of melanin and is highly safe. The melanin production inhibitor is represented by general formula (1) (excluding clotrimazole) and/or a pharmacologically acceptable salt thereof. In the formula, A1, A2 and A3 are independently selected from a hydrogen atom, an aryl group which may have a substituent, and an aromatic heterocyclic group which may have a substituent. At least one of A1, A2 and A3 is selected from the aryl group and the aromatic heterocyclic group, the total number of carbon atoms contained in A1, A2 and A3 is 6 to 50 and, when at least two of A1, A2 and A3 represent the aryl groups or the aromatic heterocyclic groups, the adjacent two aryl or aromatic heterocyclic groups may be bound to each other via an alkyl chain or an alkenyl chain to form a ring; m represents an integer of 0 to 2; X represents a hetero atom, a hydrogen atom, or a carbon atom; R1 and R2 are independently selected from a hydrogen atom and an oxo group. When one of R1 and R2 is an oxo group, the other is not present. R3 is selected from a hydrogen atom, and a C1-8 hydrocarbon group in which one or some of hydrogen atoms or carbon atoms may be substituted by a hetero atom or hetero atoms. The number of R3's present in the compound corresponds to X and, when two or more R3's are present, the R3's are independently present and the adjacent two R3's may be bound to each other to form, together with X, a ring, and the terminal of R3 may be bound to a carbon atom to which A1, A2 and A3 are bound, thereby forming a ring.
Optimized S-trityl-l-cysteine-based inhibitors of kinesin spindle protein with potent in vivo antitumor activity in lung cancer xenograft models
Good, James A. D.,Wang, Fang,Rath, Oliver,Kaan, Hung Yi Kristal,Talapatra, Sandeep K.,Podgórski, Dawid,MacKay, Simon P.,Kozielski, Frank
supporting information, p. 1878 - 1893 (2013/05/08)
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
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.
Synthesis and electron transfer characteristics of a neutral, low-band-gap, mixed-valence polyradical
Reitzenstein, Doerte,Quast, Tatjana,Kanal, Florian,Kullmann, Martin,Ruetzel, Stefan,Hammer, Maria S.,Deibel, Carsten,Dyakonov, Vladimir,Brixner, Tobias,Lambert, Christoph
experimental part, p. 6641 - 6655 (2011/10/02)
A polyradical consisting of alternating triarylamine and perchlorotriphenylmethyl radical moieties was synthesized by Horner-Emmons reaction. This compound is the first polymeric neutral mixed-valence compound that shows an intervalence charge transfer (I
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
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
Arnett, Edward M.,Flowers II, Robert A.,Ludwig, Richard T.,Meekhof, Alison E.,Walek, Stuart A.
, p. 499 - 513 (2007/10/03)
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.
Tris(4-methoxyphenyl)methanol
Ferguson, George,Glidewell, Christopher,Patterson, Iain L. J.
, p. 420 - 423 (2007/10/03)
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].
Chemoselective Preparation of Ketones by the Grignard Reaction of N-Acylpyrazoles
Kashima, Choji,Kita, Isanobu,Takahashi, Katsumi,Hosomi, Akira
, p. 25 - 28 (2007/10/02)
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.
Reactivities of triarylmethyl and diarylmethyl cations with azide ion investigated by laser flash photolysis. Diffusion-controlled reactions
McClelland, Robert A.,Kanagasabapathy,Banait, Narinder S.,Steenken, Steen
, p. 1009 - 1014 (2007/10/02)
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.
