Evidence for intramolecular electrostatic catalysis as a possible mechanism in the hydrolysis of vinyl ethers in aqueous solution

Halvarsson, Torbjoern; Bergman, N.-A.

doi:10.1021/jo00001a047

Cited by 4 publications

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“…The following results for catalysis by hydroxide ion and Brønsted bases of the deprotonation of weak neutral and cationic α-carbonyl carbon acids to give negatively charged enolates and neutral organic zwitterions, respectively, show that there is a systematic dependence of the relative reactivity of anionic and neutral base catalysts on the charge at the reacting carbon acid, − and they define the magnitude of these effects.…”

Section: Discussionmentioning

confidence: 99%

Formation and Stability of Organic Zwitterions in Aqueous Solution: Enolates of the Amino Acid Glycine and Its Derivatives

2000

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Second-order rate constants for carbon deprotonation of glycine zwitterion, N-protonated glycine methyl ester, betaine methyl ester, and betaine by deuterioxide ion in D2O have been determined by following deuterium exchange into these carbon acids in buffered solutions at 25 °C and I = 1.0 (KCl) by 1H NMR spectroscopy. The data were used to calculate the following carbon acidities for glycine zwitterion and its derivatives in aqueous solution: +H3NCH2CO2 -, pK a = 28.9 ± 0.5; +H3NCH2CO2Me, pK a = 21.0 ± 1.0; +Me3NCH2CO2Me, pK a = 18.0 ± 1.0; +Me3NCH2CO2 -, pK a = 27.3 ± 1.2. The rate constants for deprotonation of glycine methyl ester by Brønsted base catalysts are correlated by β = 0.92. Two important differences between structure−reactivity relationships for deprotonation of neutral α-carbonyl carbon acids and cationic esters are attributed to the presence of the positively charged ammonium substituent at the latter carbon acids: (1) The smaller negative deviation of log k DO from the Brønsted correlation for deprotonation of +H3NCH2CO2Me than for deprotonation of ethyl acetate is attributed to stabilization of the transition state for enolization by electrostatic interactions between DO- and the positively charged ammonium substituent. (2) The positive deviation of log k HO for deprotonation of cationic esters from the rate−equilibrium correlation for deprotonation of neutral α-carbonyl carbon acids is attributed to both transition-state stabilization by these same electrostatic interactions and movement of negative charge at the product enolate away from oxygen and onto the α-carbon. This maximizes the stabilizing interaction of this negative charge with the positively charged ammonium substituent and leads to a reduction in the Marcus intrinsic barrier to proton transfer, as a result of the decreased resonance stabilization of the enolate. The implications of these results for enzymatic catalysis of racemization of amino acids is discussed.

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Section: Discussionmentioning

confidence: 99%

Formation and Stability of Organic Zwitterions in Aqueous Solution: Enolates of the Amino Acid Glycine and Its Derivatives

2000

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Regioselective unusual formation of spirocyclic 4‐{3′‐benzo(2′,3′‐dihydro)furo}‐9‐methyl‐2,3,9‐trihydrothiopyrano [2,3‐b]indole by acid‐catalyzed reaction of enol ethers

Majumdar

Alam

Chattopadhyay

2009

Journal of Heterocyclic Chem

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in Wiley InterScience (www.interscience.wiley.com). Spirocyclic 4-{30 -benzo(2 0 ,3 0 -dihydro)furo}-9-methyl-2,3,9-trihydrothiopyrano[2,3-b]indoles are regioselectively synthesized by treating suitable enol ethers, 4-aryloxymethylene-9-methyl-2,3,9-trihydrothiopyrano[2,3-b]indoles with H 2 SO 4 in dichloromethane-methanol-water. The substrates for the aforesaid reaction are in turn synthesized by the thio-Claisen rearrangement of 2-(4 0 -aryloxybut-2 0 -ynylthio)-1-methylindoles.

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Recent Advances in Designed Local Electric Fields

Blyth¹,

Coote²

2021

Effects of Electric Fields on Structure and Reactivity

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Remote designed local electric fields (D-LEFs) are emerging as a practical strategy for the manipulation of chemical reactivity. This chapter surveys the historical use of D-LEFs, and explores the theory and practical use of Brønsted acids and bases, metal ions, and ion-pairs as novel effectors of D-LEFs, with key concepts such as polarisation illustrated using recent theoretical and experimental case studies. Particular attention is paid to the use of D-LEFs in concert with existing catalysts and catalytic strategies, within photochemistry and excited states, and in the manipulation of regio- and diastereoselectivity. Prospective advances in the efficient use of D-LEFs are also surveyed, and the need for further experimental validation of D-LEF effects is emphasised.

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Evidence for intramolecular electrostatic catalysis as a possible mechanism in the hydrolysis of vinyl ethers in aqueous solution

Cited by 4 publications

References 0 publications

Formation and Stability of Organic Zwitterions in Aqueous Solution: Enolates of the Amino Acid Glycine and Its Derivatives

Formation and Stability of Organic Zwitterions in Aqueous Solution: Enolates of the Amino Acid Glycine and Its Derivatives

Regioselective unusual formation of spirocyclic 4‐{3′‐benzo(2′,3′‐dihydro)furo}‐9‐methyl‐2,3,9‐trihydrothiopyrano [2,3‐b]indole by acid‐catalyzed reaction of enol ethers

Recent Advances in Designed Local Electric Fields

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