- Palladium-catalyzed intermolecular alkene carboacylation via ester C-O bond activation
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We report palladium-catalyzed intermolecular carboacylation of alkenes with ester electrophiles and tetraarylborate nucleophiles. Bicyclic alkenes react with a variety of pentafluorophenyl benzoate and alkanoate esters and sodium tetraarylborates to form ketone products in ≤99% yields. These reactions occur in the absence of a directing group and demonstrate esters are competent acyl electrophiles for intermolecular alkene carboacylation reactions.
- Banovetz, Haley K.,Vickerman, Kevin L.,David, Colton M.,Alkan, Melisa,Stanley, Levi M.
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supporting information
p. 3507 - 3512
(2021/05/10)
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- Formation of 1-hydroxymethylene-1,1-bisphosphinates through the addition of a silylated phosphonite on various trivalent derivatives
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An easily handled one-pot synthetic procedure was previously developed for the synthesis of bisphosphinates starting from acyl chlorides. Herein, other trivalent derivatives as acid anhydrides and activated esters were tested to form various bisphosphinates. This modulation of the reactivity can be controlled according to the nature of the acid derivative for the use of sensitive and functionalized substrates.
- Dussart-Gautheret, Jade,Deschamp, Julia,Monteil, Maelle,Gager, Olivier,Legigan, Thibaut,Migianu-Griffoni, Evelyne,Lecouvey, Marc
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p. 14559 - 14569
(2020/12/29)
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- C-F Activation in Perfluorinated Arenes with Isonitriles under UV-Light Irradiation
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Due to the great value of fluorinated arenes in agrochemistry, medicinal chemistry and materials science, development of methods for preparation of fluorinated arenes is of high importance. They can be either accessed by arene fluorination or by partial arene defluorination. However, the carbon-fluorine bond belongs to the strongest σ-bonds, which renders C-F activation highly challenging. Here it is shown that aryl and alkyl isonitriles efficiently activate the strong C-F bond in perfluoroarenes by simple UV irradiation under mild conditions. Reactions proceed by formal direct insertion of the isonitrile into the C-F bond without any transition metal. Activation occurs at arene C-F bonds whereas aliphatic C-F bonds remain unreacted. For selected perfluoroarenes C-F activation occurs with high regioselectivity and resulting imidoyl fluorides are transformed into other valuable compounds. Theoretical studies give insights into the reaction mechanism.
- Dewanji, Abhishek,Mück-Lichtenfeld, Christian,Bergander, Klaus,Daniliuc, Constantin G.,Studer, Armido
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supporting information
p. 12295 - 12298
(2015/08/25)
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- Silver triflate catalyzed acetylation of alcohols, thiols, phenols, and amines
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A variety of alcohols, thiols, phenols, and amines were subjected to acetylation reaction using acetic anhydride in the presence of catalytic quantity of silver triflate. The method described has a wide range of applications, proceeds under mild conditions, does not involve cumbersome workup, and the resulting products are obtained in high yields within a reasonable time. Georg Thieme Verlag Stuttgart · New York.
- Das, Rima,Chakraborty, Debashis
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experimental part
p. 1621 - 1625
(2011/06/25)
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- TUBULYSIN D ANALOGUES
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The present invention provides novel tubulysin analogues, methods of making and methods of using such analogues and conjugates thereof. The essential features for the potent cytotoxicity of tubulysin D have been established for the first time by the synthesis and evaluation of a series of analogues. By identifying functionality that surprisingly is not necessary for activity, highly potent cell-growth inhibitors have been developed that are smaller and considerably more stable than tubulysin D.
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Page/Page column 42
(2009/03/07)
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- Design, synthesis, and biological properties of highly potent tubulysin D analogues
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Ten analogues of tubulysin D were synthesized and assayed against established mammalian cell lines, including cancer cells measuring inhibition of cell growth by an MTT assay. These experiments establish for the first time the essential features for the potent cytotoxicity of tubulysin D. The activities of analogues 2 to 5 demonstrate that numerous modifications may be introduced at the C-terminus of the natural product with only modest loss in activity, while the activities of analogues 6 to 8 suggest that a basic amine must be present at the N-terminus to maintain activity. Most surprisingly, analogue 10 establishes that replacement of the chemically labile O-acyl N,O-acetal with the stable N-methyl group results in almost no loss in activity. In aggregate, these structure-activity relationships enable the design of analogues such as 11 that are smaller and considerably more stable than tubulysin D but that maintain most of its potent cell-growth inhibitory activity.
- Patterson, Andrew W.,Peltier, Hillary M.,Sasse, Florenz,Ellman, Jonathan A.
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p. 9534 - 9541
(2008/12/22)
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- Selective esterifications of alcohols and phenols through carbodiimide couplings
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Esterification of carboxylic acids capable of forming ketene intermediates upon treatment with carbodiimides permits the selective acylation of alcohols in the presence of phenols lacking strong electron-withdrawing groups. The selectivity of acylations involving highly acidic phenols could be reversed through the addition of catalytic amount of acid. Esterification of other carboxylic acids was found to proceed through the formation of symmetric anhydrides and provide the opposite chemoselectivity. In both cases the relative acylation rates of substituted phenols are consistent with a reaction mechanism involving an attack of phenolate anions on electrophilic intermediates such as ketenes and symmetric anhydrides, with the carbodiimides serving both as an activating reagent and as a basic catalyst.
- Shelkov, Rimma,Nahmany, Moshe,Melman, Artem
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p. 397 - 401
(2007/10/03)
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- Structure-reactivity correlations for reactions of substituted phenolate anions with acetate and formate esters
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The reactions of substituted phenolate anions with m-nitrophenyl, p-nitrophenyl, and 3,4-dinitrophenyl formates follow nonlinear Br?nsted-type correlations that might be taken as evidence for a change in the rate-limiting step of a reaction that proceeds through a tetrahedral addition intermediate. However, the correlation actually represents two different Br?nsted lines that are defined by meta- and para-substituted phenolate anions and by meta- and para-substituted o-chlorophenolate anions. A concerted mechanism for both acetyl- and formyl-transfer reactions is supported by the absence of a detectable change in the Br?nsted slope at ΔpK = 0 for the attacking and leaving phenolate anions within each class of Br?nsted correlations. Regular increases in the dependence of log k on the pKa of the nucleophile with increasing pKa of the leaving group correspond to a positive interaction coefficient pxy = ?β1g/?(pKnuc) = ?βnuc/?(pK1g). The observation of two different Br?nsted lines for the reactions of substituted phenolate anions with phenyl acetates is attributed to a steric effect that decreases the rate of reaction of substituted o-chlorophenolate anions by 25-50%. The reactions of meta- and para-substituted phenolate and o-chlorophenolate anions with substituted phenyl acetate esters follow values of βnuc = 0.53-0.66 and -β1g = 0.50-0.63. The reactions of meta- and para-substituted phenolate anions with formate esters are ~ 103 times faster and follow smaller values of βnuc = 0.43-0.64 and -β1g = 0.31-0.48. However, the reactions of meta- and para-substituted o-chlorophenolate anions with the same formate esters follow larger values of βnuc = 0.63-0.90 and -β1g = 0.46-0.90. The large values of βnuc and -β1g for the reactions of substituted o-chlorophenolate anions with formate esters may arise from destabilization by the o-chloro group of a stacking interaction that is present in the transition state for reactions of formate esters, but not acetate esters.
- Stefanidis, Dimitrios,Cho, Sayeon,Dhe-Paganon, Sirano,Jencks, William P.
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p. 1650 - 1656
(2007/10/02)
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- An Open Transition State in Carbonyl Acyl Group Transfer in Aqueous Solution
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The second-order rate constants have been measured for the reaction of substituted phenolate ions with 2,4-dinitrophenyl acetate, 2,4-dinitrophenyl 4-methoxy-2,6-dimethylbenzoate and acetic anhydride in aqueous solution at 25 deg C.The data are over a wide range of phenolate ion basicity and obey good Broensted equations which have βnuc values of, respectively, 0.57 +/- 0.03, 0.15 +/- 0.07 and 0.59 +/- 0.05.The principal conclusion of this work is that the identity reaction of 2,4-dinitrophenolate ion with 2,4-dinitrophenyl 4-methoxy-2,6-dimethylbenzoate has anopen transition state, namely one with very weak bonds to entering and departing ligands.The transition state possesses a Kreevoy tightness parameter (τ) of 0.18.The open transition state arises from the stabilising effect of the acyl group substituents on the benzoylium ion and their destabilising effect on the putative tetrahedral intermediate as well as the weak basicities of the nucleophile and nucleofuge.This is the first example of an open transition state in an acyl group transfer which does not require the assistance of a negatively charged internal nucleophile.The data for 2,4-dinitrophenyl acetate may be employed to calculate an identity rate constant (kii) for the reaction of 2,4-dinitrophenolate ion with the ester.This data may be fitted to a theoretical Lewis-Kreevoy plot (log kii vs. pKi) possessing both positive and negative values of βii (slope of the line).Microscopic medium effects place a limit to the accuracy of predictions of rate constants, including kii, from linear free energy relationships.
- Ba-Saif, Salem A.,Colthurst, Matthew,Waring, Mark A.,Williams, Andrew
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p. 1901 - 1908
(2007/10/02)
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- Concerted Acetyl Group Transfer between Substituted Phenolate Ion Nucleophiles: Variation of Transition-State Structure as a Function of Substituent
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Second-order rate constants (kArO) have been measured for the concerted displacement of aryl oxide from aryl acetates in aqueous solution by substituted phenoxide ions.Values of kArO obey linear Bronsted correlations when either the leaving group or the attacking phenolate ion structures are varied.The Bronsted coefficients obey the equations βnuc = 0.20pK1g - 0.68 and β1g = 0.15pKnuc - 1.73 to a good degree of precision, and the variation indicates that the structure of the transition-state changes within the range of phenolate ions studied; this alsoprovides confirmation that a concerted mechanism operates.The equations for βnuc and β1g predict the equation (log kii = 0.17pKa2 - 2.41pKa + C) for kii, the rate constant for the reaction of aryl oxide ion with acetates bearing identical aryl oxide leaving groups.The identity rate constants may be interpolated from the observed rate constants (kArO) and exhibit excellent fit to the above equation with the single disposable parameter, C, set at 6.5.This is the first report of curvature in a Bronsted plot of identity rate constants.Effective charge development and loss on leaving and attacking oxyanions is fully balanced in the transition state when entering and leaving nucleophiles have a pKa of 7.1.Tetrahedral or acylium ion-like transition-state structures are predicted for hypothetical phenols with pKa's of 11.7 and 2.0, respectively.
- Ba-Saif, Salem,Luthra, Ajay K.,Williams, Andrew
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p. 2647 - 2652
(2007/10/02)
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- Oxiranes from Methylenation of the Ester Carbonyl Group by Diazomethane
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Esters suitably substituted by electronegative groups were found to react with diazomethane with the anchimeric assistance of a ?-system or a trifluoromethyl group close to the ester oxygen to yield 2-alkoxy-2-substituted-oxiranes in good to excellent yields without catalysts.
- Strazzolini, Paolo,Verardo, Giancarlo,Giumanini, Angelo G.
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p. 3321 - 3325
(2007/10/02)
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- Concertedness in Acyl Group Transfer in Solution: A Single Transition State in Acetyl Group Transfer between Phenolate Ion Nucleophiles
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Rate constants have been measured for nucleophilic substitution of 4-nitrophenol from 4-nitrophenyl acetate by a series of phenolate anions.The Bronsted type plot is linear for unhindered phenolate ions with pKa values significantly above and below that of the displaced 4-nitrophenol: (log kArO = 0.75pKArOH - 7.28; n = 17, r = 0.984); this is consistent with a mechanism involving a single transition state or a mechanism with an intermediate that has a very low barrier to decomposition.A small change in effective charge on the carbonyl group from reactant to transition state (measured from βnuc and the known βeq for the overall reaction) points to an almost coupled concerted mechanism for the transfer of acetyl function between phenolate ion nucleophiles.The conclusions of this work are consistent with previous results that indicate relatively stable tetrahedral intermedates in reactions at reactive acyl centers; a spectrum of mechanisms exists for substitution reactions of acyl functions in solution that ranges from SN1 (or ElcB for an ester with an α-carbanion) through concerted to BAc2.
- Ba-Saif, Salem,Luthra, Ajay K.,Williams, Andrew
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p. 6362 - 6368
(2007/10/02)
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