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, depending on the reactivity of the alkoxide. Likewise, the monobasic sodium salts of chloral and fluoral hydrate exhibit similar rate enhancements, relative to their respective hydrates.

Photoredox Catalysis in Organic Chemistry

“…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).…”

Activation and Deactivation Strategies Promoted by Medium Effects for Selective Aliphatic C−H Bond Functionalization

“…[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).…”

“…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.…”

C1 Oxidation/C2 Reduction Isomerization of Unprotected Aldoses Induced by Light/Ketone

“…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).…”