- MISE EN EVIDENCE DU MECANISME "SN2 (INTERMEDIAIRE)" DANS DES SOLVOLYSES DE TOSYLATES SECONDAIRES ENCOMBRES. ABSENCE DE CORRESPONDANCE VITESSES-PRODUITS
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ks/kc ratios, representative of nucleophilic solvent assistance were obtained for solvolyses of hindered secondary substrates.Reactions products were also investigated.Failure to observe a rate-product correlation underlines the noni
- Laureillard, J.,Casadevall, A.,Casadevall,E.
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- Internal Return in the Solvolysis of Secondary Alkyl Arenesulphonates
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In highly ionizing solvolytic media, such as hexafluoropropan-2-ol, 2-adamantyl azoxytoluene-p-sulphonate gives only solvent-derived products, while in a solvent less conducive to carbonium ions such as ethanol, 2-adamantyl toluene-p-sulphonate may be detected among the solvolysis products; this demonstrates that the 2-adamantyl cation may be captured by the very weakly nucleophilic toluene-p-sulphonate anion even in a strongly nucleophilic medium and, with other results, establishes that internal return accompanies the solvolysis of 2-adamantyl toluene-p-sulphonate.
- Maskill, H.,Thompson, John T.,Wilson, Alan A.
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- The mechanism of solvolysis of 2-adamantyl azoxytosylate: Isotopic labelling, medium effect, and attempted deoxygenation studies
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Rates of solvolysis of 2-adamantyl azoxytosylate (1) have been measured over a range of temperatures in ethanoic acid, methanoic acid, 50:50 (v/v) trifluoroethanol:water, 80:20 (v/v) trifluoroethanol:water, 97:3 (w/w) trifluororoethanol:water, and 70:30 (v/v) ethanol:water. For comparison, rates of solvolysis of 2-adamantyl tosylate (2) have also been measured in 50:50, 80:20, and 90:10 (v/v) trifluoroethanol:water, and for both compounds, activation parameters have been determined. These and results published earlier allow a correlation of the two reactions and indicate that the m value for 2-adamantyl azoxytosylate solvolysis is only 0.46. This is one of the lowest m values for a reaction that is unambiguously an S(N)1 solvolysis. We have also recorded the 17O NMR spectrum of the 2-adamantyl tosylate formed from 17O-labelled 2-adamantyl azoxytosylate in deuteriochloroform, and the millimeter-wave spectrum of the nitrous oxide evolved in the hydrolysis of 18O-labelled 2-adamantyl azoxytosylate. These labelling studies have provided more detailed knowledge of the S(N)l fragmentation mechanism of 1 and exclude a mechanism of reaction via rearrangement to N- nitroso,N-(2-adamantyl),O-(p-toluenesulfonyl)hydroxylamine (5). Attempted deoxygenation of 1 to give 2-adamantyl diazotosylate (8) and a subsequent fragmentation proved unsuccessful.
- Conner, John K.,Haider, Johanna,Hill, M.N. Stuart,Maskill, Howard,Pestman, Monique
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- A facile and green protocol for nucleophilic substitution reactions of sulfonate esters by recyclable ionic liquids [bmim][X]
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Ionic liquids [bmim][X] (X = Cl, Br, I, OAc, SCN) are highly efficient reagents for nucleophilic substitution reactions of sulfonate esters derived from primary and secondary alcohols. The counter anions (X-) of the ionic liquids, [bmim][X], effectively replace the sufonates affording the corresponding substitution products such as alkyl halides, acetates, and thiocyanides in excellent yields. The newly developed protocol is very environmentally attractive because the reactions use stoichiometric amounts of ionic liquids as sole reagents in most cases and do not require additional solvents, any other activating reagents, non-conventional equipment, or special precautions. Moreover, these ionic liquids can be readily recycled without loss of reactivity, making the whole process greener.
- Liu, Yajun,Xu, Yongnan,Jung, Sun Ho,Chae, Junghyun
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supporting information
p. 2692 - 2698,7
(2012/12/12)
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- A facile and green protocol for nucleophilic substitution reactions of sulfonate esters by recyclable ionic liquids [bmim][X]
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Ionic liquids [bmim][X] (X = Cl, Br, I, OAc, SCN) are highly efficient reagents for nucleophilic substitution reactions of sulfonate esters derived from primary and secondary alcohols. The counter anions (X-) of the ionic liquids, [bmim][X], effectively replace the sufonates affording the corresponding substitution products such as alkyl halides, acetates, and thiocyanides in excellent yields. The newly developed protocol is very environmentally attractive because the reactions use stoichiometric amounts of ionic liquids as sole reagents in most cases and do not require additional solvents, any other activating reagents, non-conventional equipment, or special precautions. Moreover, these ionic liquids can be readily recycled without loss of reactivity, making the whole process greener. Georg Thieme Verlag KG Stuttgart · New York.
- Liu, Yajun,Xu, Yongnan,Jung, Sun Ho,Chae, Junghyun
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supporting information
p. 2692 - 2698
(2013/01/15)
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- Low-temperature x-ray structural studies of the ester and ether derivatives of cis- and trans-4-tert-butyl cyclohexanol and 2-adamantanol: Application of the variable oxygen probe to determine the relative σ-donor ability of C-H and C-C bonds
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Results of low-temperature X-ray structural studies for five cis-, and three trans-4-tert-butyl cyclohexanol, and six 2-adamantanol ester and ether derivatives are reported. Plots of C-OR bond distance against pKa(ROH) for derivatives of axial alcohol (5), equatorial alcohol (6) and 2-adamantanol derivatives (7) give slopes of -2.77 × 10-3, -2.86 × 10-3 and -3.05 × 10-3, respectively. Given that the relative differences in the slopes are modest, no clear distinction can be made about the relative σ-donor ability of a C-H bond and a C-C bond.
- Spiniello, Marisa,White, Jonathan M.
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p. 3094 - 3101
(2007/10/03)
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- Hyperconjugative control by remote substituents of diastereoselectivity in the oxygenation of hydrocarbons
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(figure presented) The oxidation of 2-substituted adamantanes (2) with TFDO (1) is reported. The data show a stereodifferentiation of the chemical environments induced by remote electron-withdrawing substituents which produces remarkable Z/E diastereosele
- Gonzalez-Nunez, Maria E.,Royo, Jorge,Castellano, Gloria,Andreu, Cecilia,Boix, Carmen,Mello, Rossella,Asensio, Gregorio
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p. 831 - 834
(2007/10/03)
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- Face selection in the reduction of p,p'-disubstituted 5,7-diphenyl-2- adamantanones and hydrolysis of the corresponding 2-adamantyl tosylates
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The reduction of 5,7-diphenyl-2-adamantanone with sodium borohydride in 2- propanol is affected by the introduction of a p-nitro substituent in one of the rings: the E-alcohol is obtained in small but easily measurable excess of 1.30:1. Conversely, the in
- Song,Le Noble
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- Solvolysis of Alkyl Azoxytosylates: The Link between Solvolytic Deamination and Tosylate Solvolysis
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Products of the solvolysis of 2-adamantyl azoxytosylate in acetic acid, ethanol, aqueous ethanol, trifluoroethanol, and aqueous trifluoroethanol have been analyzed by a combination of glc and hplc.The yield of 2-adamantyl tosylate by internal ion-pair combination is 32 percent in acetic acid but decreases with the increasing ionizing power of the solvent.Solvolysis products of bicyclooctan-2-yl azoxytosylate in 97:3 hexafluoropropan-2-ol:water have also been analyzed.Both systems yield hydrocarbon and solvent derived substitution products in amounts which are much closer to those obtained from solvolysisnof the corresponding tosylates than from the corresponding solvolytic deaminations even though the rate-determing step in the solvolysis of the azoxytosylates resembles closely the deaminative fragmentation.These results allow new insights into the nature of the mechanism of deamination generally.
- Conner, John K.,Maskill, Howard
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p. 342 - 348
(2007/10/02)
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- SOLVOLYSIS OF SECONDARY ALKYL AZOXYTOSYLATES. A NEW REACTION RELATED TO SOLVOLYTIC DEAMINATION AND ARENESULPHONATE SOLVOLYSIS
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The rates of solvolysis of 2-adamantyl azoxytosylate have been measured in hexafluoropropan-2-ol (HFIP), trifluoroethanol (TFE), aqueous hexafluoropropan-2-ol (97HFIP), aqueous trifluoroethanol (97TFE), aqueous ethanol (50E and 80E), and aqueous methanol (80M) at 3-5 temperatures between ca. 23 and 70 deg C, and activation parameters have been determined.The O-2H solvent kinetic isotope effect has been measured for HFIP (kH/kD 1.025 +/- 0.02 at 50.8 deg C) and secondary α-deuterium kinetic isotope effects have been determined in 97HFIP (kH/kD 1.090 +/- 0.005; 40.2 deg C), 50E (1.091 -/+ 0.006; 51.0 deg C), and 80E (1.133 -/+ 0.009; 60.9 deg C).Neither methanesulphonic acid in 80M nor pyridine in TFE gives rise to a significant rate enhancement, and there is hardly any salt effect due to low concentrations of tetrabutylammonium perchlorate in 97TFE. 2-Adamantyl tosylate is formed in parallel with solvolysis product in ethanol and weakly aqueous ethanol, and is the sole organic product from reactions in chloroform and toluene.No relatively long lived intermediate such as 2-adamantyl tosylate is involved in the reaction in 97TFE, 80M, and 90M.The kinetics and product results are satisfactorily accommodated by a mechanism involving initial unimolecular rate-determining synchronous fragmentation of the substrate to give nitrous oxide and an ion-pair.This ion-pair is then either captured by solvent to give solvolysis product or, in the less polar media, undergoes ion-pair combination to yield covalent 2-adamantyl tosyate.Bicyclooctan-2-yl azoxytosylate has also been prepared, and rates and activation parameters have been determined in 97HFIP and 80M.There is no evidence from this limited study of a mechanism different from that of the 2-adamantyl analogue.Rates and activation parameters for the solvolysis of cyclohexyl azoxytosylate have also been determined in an even more limited study using only 97HFIP.Rates are slower than those for the other two compounds, but the mechanism appears to be the same.
- Maskill, H.,Thompson, John T.,Wilson, Alan A.
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p. 1693 - 1704
(2007/10/02)
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- Solvent Effects on Solvolytic Reactivity. A Diagnostic Test for Neighboring-Group Assistance by ? Conjugation in Solvolysis Reactions
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The solvolysis rates of 13 arenesulfonates have been determined in mixtures of ethanol and water (the E-series solvents) and acetic acid and formic acid (the A-series solvents).The substrates studied include the following: neophyl (1), 2-adamantyl (2), neopentyl (3), and cyclooctyl (4) tosylates; cyclopropylcarbinyl pemsylate (5a) and tosylate (5b); exo-2-norbornyl tosylate (6); cyclobutylcarbinyl (7), cyclobutyl (8), and pinacolyl (9) brosylates; cyclopentyl (10), cyclohexyl (11), and 2-propyl (12) tosylates; and cyclopentylcarbinyl brosylate (13).Correlations of the rate data by eq 1 t(Y) = a + b log kt(neophyl-OTs)> showed that the various substrates responded differently to the examined solvent effects on the solvolytic reactivity.For compounds 2-4, linear correlations were obtained.For compounds 5-9, E-line, A-line dispersions were noted which diverged with increasing ionizing power; for compounds 10-12, parallel E-line, A-line dispersions were obtained; and for compound 13, an E-line, A-line dispersion was observed which converged with increasing ionizing power.Stastistical analyses of the rate data correlations confirmed the significance of the E or A classification of data.The results are interpreted in terms of differences in the involvement of solvent in the transition state for those solvolyses assisted by bridging from those assisted by C-C ? bond hyperconjugation.
- Roberts, Donald D.
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p. 2521 - 2526
(2007/10/02)
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- Stereochemistry and Mechanism of ?-Assisted Solvolysis of endo-Bicyclonon-6-ene-3-methyl Tosylate
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The stereochemistry of the title reaction in several solvents has been established by 2H NMR configurational analysis of the 2-adamantyl-4,4-d2 products obtained from the α,α-dideuterated reactant 6.Solvent nucleophilic attack occurs predominantly on the side of the 2-adamantyl position away from the initial reaction site, the stereoselectivity increasing with increasing solvent nucleophilicity.Tosylate ion return in each case studied exhibits mainly though less selectively the same stereochemistry, i.e., is predominantly a non-least-motion process.Solvolysis in 80percent aqueous ethanol in the presence of 0.06 M NaN3 produces only 1percent of 2-adamantyl azide.The results constitute strong evidence for reaction through bridged carbonium ions and demonstrate that the structures of the carbocations in the initial ion pairs along the direct route and the ? route to 2-adamantyl solvolysis products are markedly differentiated by the location of the counterion.
- Nordlander, J. Eric,Kotian, Kirtivan D.,Raff, Dwight E.,Grohol, William P.,Vishwanath, Vasanth M.,Winemiller, Jeffry J.
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p. 863 - 867
(2007/10/02)
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