- Nucleophilic (Radio)Fluorination of Redox-Active Esters via Radical-Polar Crossover Enabled by Photoredox Catalysis
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We report a redox-neutral method for nucleophilic fluorination of N-hydroxyphthalimide esters using an Ir photocatalyst under visible light irradiation. The method provides access to a broad range of aliphatic fluorides, including primary, secondary, and tertiary benzylic fluorides as well as unactivated tertiary fluorides, that are typically inaccessible by nucleophilic fluorination due to competing elimination. In addition, we show that the decarboxylative fluorination conditions are readily adapted to radiofluorination with [18F]KF. We propose that the reactions proceed by two electron transfers between the Ir catalyst and redox-active ester substrate to afford a carbocation intermediate that undergoes subsequent trapping by fluoride. Examples of trapping with O- and C-centered nucleophiles and deoxyfluorination via N-hydroxyphthalimidoyl oxalates are also presented, suggesting that this approach may offer a general blueprint for affecting redox-neutral SN1 substitutions under mild conditions.
- Webb, Eric W.,Park, John B.,Cole, Erin L.,Donnelly, David J.,Bonacorsi, Samuel J.,Ewing, William R.,Doyle, Abigail G.
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supporting information
p. 9493 - 9500
(2020/05/18)
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- Predictable site-selective radical fluorination of tertiary ethers
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In this communication, we disclose the first example of metal-free and site-selective radical fluorination of readily available tertiary alkyl ethers, enabled by synergistic photocatalysis and organocatalysis. This catalytic combination allows for exclusi
- Ma, Junyang,Xu, Wentao,Xie, Jin
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p. 187 - 191
(2019/11/21)
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- A Series of Deoxyfluorination Reagents Featuring OCF2Functional Groups
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Research on perfluoroalkyl ether carboxylic acids (PFECAs) as alternatives for perfluoroalkyl substances continues with the goal of protecting the environment. However, very little is known about the utilization of decomposition products of PFECAs. We report herein a new series of deoxyfluorination reagents featuring OCF2 functional groups derived from certain PFECAs. Alkyl fluorides were generated from various alcohols in ≤97% yield by these novel reagents. The mechanistic experiment verified in situ generation of carbonic difluoride (COF2).
- Cao, Wei,Chen, Qing-Yun,Guo, Yong,Su, Zhaoben,Wu, Chengying,Zhao, Shiyu
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supporting information
(2020/11/03)
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- Visible light-promoted metal-free C-H activation: Diarylketone-catalyzed selective benzylic mono- and difluorination
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We report herein an operationally simple method for the direct conversion of benzylic C-H groups to C-F. We show that visible light can activate diarylketones to abstract a benzylic hydrogen atom selectively. Adding a fluorine radical donor yields the benzylic fluoride and regenerates the catalyst. The selective formation of mono- and difluorination products can be achieved by catalyst control. 9-Fluorenone catalyzes benzylic C-H monofluorination, while xanthone catalyzes benzylic C-H difluorination. The scope and efficiency of this new C-H fluorination method are significantly better than those of the existing methods. This is also the first report of selective C-H gem-difluorination.
- Xia, Ji-Bao,Zhu, Chen,Chen, Chuo
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supporting information
p. 17494 - 17500
(2014/01/06)
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- Tetramethylfluoroformamidinium hexafluorophosphate (TFFH) as a mild deoxofluorination reagent
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The solid, air-stable peptide coupling reagent TFFH (tetramethylfluoroformamidinium hexafluorophosphate) was found to activate a variety of alcohols towards deoxofluorination. These conditions are compatible with carbonyl functional groups thus offering interesting possibilities for the application to sensitive molecules. Georg Thieme Verlag Stuttgart · New York.
- Bellavance, Gabriel,Dubé, Pascal,Nguyen, Bao
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experimental part
p. 569 - 572
(2012/04/17)
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- Evidence for Carbocation Intermediates in the TiO2-Catalyzed Photochemical Fluorination of Carboxylic Acids
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Laser flash photolysis/transient absorbance spectroscopy was used to determine the mechanism of photo-Kolbe fluorination of carboxylic acids, RCOOH --> RF, at colloidal TiO2 suspensions in acetonitrile.Transient absorption spectra of Ph3C(+), Ph3C(*), Ph2CH(*) and Ph2CH(+) were observed from the photooxidation of Ph3CCOOH and Ph2CHCOOH at TiO2 using 355-nm excitation.Transient decays, monitored in the presence and absence of fluoride ions, showed that the carbocations reacted rapidly with fluoride, but the neutral radicals did not.By varying the laser intensity, it wa s found that the photooxidation of Ph3CCOOH to Ph3C(*) at TiO2 occured via a single-photon process, while the formation of of Ph3C(+) required two photons.This finding is in agreement with the parabolic light intensity dependence of initial reaction rates in bulk photolysis experiments.Although fluoride is strongly adsorbed on the TiO2 surface in acetonitrile solution, the oxidizing power of photogenerated holes could be increased by coordinating HF to F(-), and therefore the threshold for oxidative photochemical fluorination was extented to more positive potentials.In this way less easily oxidized carboxylic acids RCOOH could be converted to RF.
- Lai, Cuiwei,Kim, Yeong Il,Wang, Chong Mou,Mallouk, Thomas E.
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p. 1393 - 1399
(2007/10/02)
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- The reactions of copper-dibromodifluoromethane-amide systems with alcohols
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1,1,1-Trifluoro-2-arylethanes can be prepared by the trifluoromethyldehydroxylation of benzyl alcohols using the copper-dibromodifluoromethane-amide reaction system, although the yields are low.The mechanism of the reaction may involve chelation of the substrate to copper so that α-substituted benzyl alcohols and other alcohols are unreactive.
- Clark, James H.,McClinton, Martin A.,Blade, Robert J.
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p. 257 - 267
(2007/10/02)
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- Conformational Preference of the Fluoromethyl Group in Some Benzyl Fluorides: a 13C N.M.R. Study
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A number of model benzyl fluoride systems have been synthesized, end their proton-decoupled natural-abundance 13C n.m.r. spectra recorded and assigned.An analysis of the long-range five-bond coupling constants (5JCF) indicates that these parame
- Adcock, William,Abeywickrema, Anil N.
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p. 181 - 187
(2007/10/02)
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