2004
DOI: 10.1039/b405074f
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Rate constants for hydrogen abstraction from alkoxides by a perfluoroalkyl radical. An oxyanion accelerated processElectronic supplementary information (ESI) available: Tables of kinetic data and plots of kinetic data. See http://www.rsc.org/suppdata/ob/b4/b405074f

Abstract: A combination of laser flash photolysis and competitive kinetic methods has been used to measure the absolute bimolecular rate constants for hydrogen atom abstraction in water from a series of fluorinated alkoxides and aldehyde hydrates by the perfluoroalkyl radical, *CF2CF2OCF2CF2SO3- Na+. The bimolecular rate constants observed for the beta-fluorinated alkoxides were in the 10(5) M(-1) s(-1) range, such rates representing enhancements (relative to the respective alcohols) of between 100 and almost 1000-fold,… Show more

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Cited by 16 publications
(14 citation statements)
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“…Here, a hydrogen bonding interaction between the phosphate and the alcohol induces a drastic weakening of the α-hydroxy C–H bonds and, in addition, increases the hydricity of the C–H bonds. 82 As a result, the highly electrophilic radical cation ( 49 ), formed via oxidation of quinuclidine, can readily abstract an activated α-hydroxy C–H bond. The resultant α-hydroxy radical is highly nucleophilic and is readily trapped by electron-deficient alkenes to ultimately deliver functionalized butyrolactone products (upon lactonization of the alkylated alcohol).…”
Section: Dual Photoredox Organocatalysis: Hydrogen Atom Transfermentioning
confidence: 99%
“…Here, a hydrogen bonding interaction between the phosphate and the alcohol induces a drastic weakening of the α-hydroxy C–H bonds and, in addition, increases the hydricity of the C–H bonds. 82 As a result, the highly electrophilic radical cation ( 49 ), formed via oxidation of quinuclidine, can readily abstract an activated α-hydroxy C–H bond. The resultant α-hydroxy radical is highly nucleophilic and is readily trapped by electron-deficient alkenes to ultimately deliver functionalized butyrolactone products (upon lactonization of the alkylated alcohol).…”
Section: Dual Photoredox Organocatalysis: Hydrogen Atom Transfermentioning
confidence: 99%
“…[34] A1 00, 277, and 962-fold increase in the k H value was measured on going from 1,1,1-trifluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), and 2,2,2-trifluoroethanol (TFE), respectively,t o the corresponding alkoxides.V ery interestingly,the measured k H values were also significantly higher than those measured for HATf rom the corresponding non-fluorinated alcohols (for example, k H = 1.2 10 4 ,8 0, and 7.7 10 4 m À1 s À1 ,f or CH 3 CH 2 OH, CF 3 CH 2 OH, and CF 3 CH 2 O À Na + ,respectively). [34] A1 00, 277, and 962-fold increase in the k H value was measured on going from 1,1,1-trifluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), and 2,2,2-trifluoroethanol (TFE), respectively,t o the corresponding alkoxides.V ery interestingly,the measured k H values were also significantly higher than those measured for HATf rom the corresponding non-fluorinated alcohols (for example, k H = 1.2 10 4 ,8 0, and 7.7 10 4 m À1 s À1 ,f or CH 3 CH 2 OH, CF 3 CH 2 OH, and CF 3 CH 2 O À Na + ,respectively).…”
Section: Acid-base Interactionsmentioning
confidence: 99%
“…Aq uantitative evaluation of the extent of a-CÀH activation by OH deprotonation was provided by Dolbier and co-workers through the measurement of absolute bimolecular rate constants for HAT( k H )f rom fluorinated alkoxides to the water-soluble perfluorinated radical CCF 2 CF 2 OCF 2 CF 2 SO 3 À Na + . [34] A1 00, 277, and 962-fold increase in the k H value was measured on going from 1,1,1-trifluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), and 2,2,2-trifluoroethanol (TFE), respectively,t o the corresponding alkoxides.V ery interestingly,the measured k H values were also significantly higher than those measured for HATf rom the corresponding non-fluorinated alcohols (for example, k H = 1.2 10 4 ,8 0, and 7.7 10 4 m À1 s À1 ,f or CH 3 CH 2 OH, CF 3 CH 2 OH, and CF 3 CH 2 O À Na + ,respectively). It was pointed out that this high reactivity derives from ac ombination of the bond-weakening effect of the alkoxide functionality and the increased electron density of the a-CÀH bonds that favor HATtothe strongly electrophilic perfluorinated carbon-centered radical.…”
Section: Acid-base Interactionsmentioning
confidence: 99%
“…Thea nomeric hydroxy group of 1a is deprotonated by NaOH to form the alkoxide 5.T he formation of 5 induces abstraction of hydrogen from the anomeric CÀHbond by the triplet-excited ketone. [19] With the resulting radical pair of 6 and B,aproton transfers from 6 to B to afford the aldose radical 7 and ketyl radical anion C.T he radical 7 undergoes spin-center shift to form the lactone 8 with ar adical center located at C2. Then, C transfers asingle electron to 8 to give an a anion, that is,the enolate of lactone 9 with regeneration of BPSS.Protonation of 9 with water occurs in adiastereoselective manner,a sw ith the case of hydration of glucal, [20] to give lactone 10.Finally, 10 is hydrolyzed by NaOH to furnish sodium 2-deoxy-d-gluconate (2a).…”
Section: Angewandte Chemiementioning
confidence: 99%