- 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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- Photofluorination of Aliphatic C-H Bonds Promoted by the Phthalimide Group
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Aliphatic C-H fluorination of phthalimide derivatives with Selectfluor was investigated under photoirradiation conditions. The reaction did not require any additive or catalyst and afforded C-H fluorinated products in moderate to good yields. It is likely
- Egami, Hiromichi,Masuda, Shuya,Kawato, Yuji,Hamashima, Yoshitaka
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- Direct, visible light-sensitized benzylic C[sbnd]H fluorination of peptides using dibenzosuberenone: selectivity for phenylalanine-like residues
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A visible light-sensitized benzylic sp3C[sbnd]H fluorination protocol using dibenzosuberenone (5?mol?%) and Selectfluoris optimized for the direct functionalization of phenylalanine-like residues in short chain peptides. Amino acids, dipeptides, and tripeptides undergo benzylic fluorination with remarkable regioselectivity in the presence of protected basic, acidic, and nonpolar side chains (including those with tertiary sites). Additionally, protecting group compatibility, a gram scale application, and competition experiments were explored.
- Bume, Desta Doro,Pitts, Cody Ross,Jokhai, Rayyan Trebonias,Lectka, Thomas
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p. 6031 - 6036
(2016/09/16)
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- Photocatalyzed benzylic fluorination: Shedding "light" on the involvement of electron transfer
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The photocatalyzed oxidation of benzylic compounds by 1,2,4,5-tetracyanobenzene (TCB) in the presence of Selectfluor provides a synthetically efficient route to electron deficient, less substituted, and otherwise inaccessible benzylic fluorides. The virtue of this system is multifold: it is metal-free and mild, and the reagents are inexpensive. Mechanistically, the data suggest the intimate formation of intermediate radical cations in the key radical forming step, as opposed to a concerted hydrogen atom transfer process.
- Bloom, Steven,McCann, Michael,Lectka, Thomas
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supporting information
p. 6338 - 6341
(2015/01/16)
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