Merging Visible-Light Photocatalysis and Transition-Metal Catalysis in Three-Component Alkyl-Fluorination of Olefins with a Fluoride Ion

Article abstract of DOI:10.1021/acs.orglett.8b01658

The light-induced, Ru-catalyzed three-component alkyl-fluorination of olefins under mild reaction conditions is reported. This carbofluorination reaction features a wide substrate scope and good functional group tolerance. A key advantage of this photoredox reaction is the use of nucleophilic fluoride and generic alkyl groups. Late-stage functionalizations are achieved, and a copper-assisted oxidative quenching mechanism is proposed based on the mechanistic studies.

Full text of DOI:10.1021/acs.orglett.8b01658

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Merging Visible-Light Photocatalysis and Transition-Metal Catalysis
in Three-Component Alkyl-Fluorination of Olefins with a Fluoride
Ion
Weili Deng,† Weiwei Feng,† Yajun Li,*,† and Hongli Bao*,†,‡
†Key Laboratory of Coal to Ethylene Glycol and Its Related Technology, Center for Excellence in Molecular Synthesis, Fujian
Institute of Research on the Structure of Matter, University of Chinese Academy of Sciences, 155 Yangqiao Road West, Fuzhou,
Fujian 350002, People’s Republic of China
‡University of Chinese Academy of Sciences, Beijing, 100049, People’s Republic of China
S
* Supporting Information
ABSTRACT: The light-induced, Ru-catalyzed three-component alkyl-fluori-
nation of olefins under mild reaction conditions is reported. This
carbofluorination reaction features a wide substrate scope and good functional
group tolerance. A key advantage of this photoredox reaction is the use of
nucleophilic fluoride and generic alkyl groups. Late-stage functionalizations are
achieved, and a copper-assisted oxidative quenching mechanism is proposed
based on the mechanistic studies.
Scheme 1. Olefin Carbofluorination with Various Carbon
Source and Photocatalysis
he catalytic site-specific incorporation of fluorine into
Torganic molecules is a challenging and promising strategy
for the construction of various fluoro-organic compounds,1
which are of great interest in pharmaceuticals, agrochemicals,
and other functional materials.2 Selective vicinal carbofluori-
nation of unsaturated carbon−carbon double bonds is an
efficient method for conversion of olefins into valuable
fluorochemicals with more complex structures.3,4 As exempli-
fied in Scheme 1a, describing the carbofluorination of olefins,
only a few catalytic reactions have been documented and there
remains a significant demand for achievement of a challenging
and sought-after reaction diversity of olefin carbofluorination.
In most of the recent advances on vicinal carbofluorination
of olefins, developments have been mainly achieved on
(Meerwein-type) aryl-fluorination by Toste,4a Gouverneur,4b
Tu,4c Heinrich,4d and Tang4e et al., electrophilic cyano-
fluorination by Dilman,4g carbonylative oxycarbonyl-fluorina-
tion by Liu,4h decarboxylative acyl-fluorination by Duan,4i
oxidative trifluoromethyl-fluorination by Qing,4j oxycarbonyl-
4l
methyl-fluorination by Li4k,m and Szabo, and intramolecular
́
alkyl migration assisted alkyl-fluorination by Alexakis4n and
Zhu4o et al. Most of the reported olefin carbofluorinations are
exclusively compatible with highly reactive, oxidizing, and
electrophilic “F+” sources, such as Selectfluor, NFSI,
fluoroiodine reagents, etc. because the high-valent “F+” ion
can act as an oxidant and enable the smooth turnover of the
reaction.5,1f To the best of our knowledge, there is still a lack of
methods for olefin carbofluorination with the nucleophilic
fluoride.6 Furthermore, methodologies for alkyl-fluorination of
olefins with a generic alkyl group are also extremely rare and
highly sought after.7,8 It is worth mentioning that Li’s group
quite recently reported a copper mediated/catalyzed trifluor-
omethyl- and trichloromethyl-fluorination of unactivated
alkenes with fluoride ions.7d
Compared to the existing methods for olefin carbofluorina-
tion using the electrophilic “F+” ion, if the nucleophilic fluoride
is used as the fluorine source, an oxidative reagent or reactant
Received: May 25, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b01658
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
might be necessary to complete the reaction, since atom
transfer radical addition (ATRA) seems unlikely to happen
with a fluorine atom.9 In 2014, Nicewicz et al. reported a
visible-light-driven, anti-Markovnikov hydrofluorination of
olefins via photoredox catalysis in a reductive quenching
system (Scheme 1b-i).10 In addition, there are rare examples of
photoinduced olefin carbofluorination.11 We postulate that it
should be possible to use oxidative alkyl reagents12 and
photocatalysis13 to achieve the desired olefin carbofluorination
with generic alkyl groups and a fluoride (Scheme 1b-ii).
In this paper, we report a photoredox-catalyzed three-
component alkyl-fluorination of olefins with a fluoride ion and
oxidative alkyl reagents (Scheme 1c). This method has the
following features: first, use of the nucleophilic fluoride instead
of an electrophilic “F+” ion as the fluorine source for the olefin
carbofluorination; second, use of generic alkyl groups from an
oxidative alkyl source for the olefin carbofluorination; and
third, use of photocatalysis in an oxidative quenching system14
for the olefin carbofluorination.
product either (Table 1, entry 6). While a reduced amount of
Et3N·3HF leads to a lower yield (Table 1, entries 7 and 8 vs 2),
an increased amount of Et3N·3HF enhances the performance
of this reaction (Table 1, entry 9). The reaction fails to
proceed in the absence of either ruthenium or light (Table 1,
entry 10). This result implies that the copper additive cannot
trigger the reaction, but plays a very important role in the
catalytic cycle. Finally, it is found that 2 mol % of Cu(OAc)2
can afford an identical performance and offer an isolated yield
as high as 76% (Table 1, entry 11).
With these optimized reaction conditions in hand, the
substrate scope of the olefins was studied, and the results are
shown in Table 2. Styrenes containing a variety of electron-
a b
,
Table 2. Substrate Scope of Olefins
Our hypothesis concerning the photoinduced carbofluori-
nation of olefins was examined with a model reaction involving
styrene (1a), lauroyl peroxide (LPO, 2a), and triethylamine
trihydrofluoride (Et3N·3HF) irradiated with 18 W blue LEDs
in the presence of a ruthenium-based catalyst (Table 1).15 The
a
Table 1. Olefin Alkyl-Fluorination Reaction Optimization
b
entry
additive (10 mol %)
yield (%)
1
2
3
4
−
40
72
69
57
0
0
49
61
Cu(OAc)2
CuF2
CuTC
Cu(OAc)2
CuF2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
c
5
d
6
e
7
8
f
g
9
79
trace
78(76)
a
1 (0.5 mmol, 1.0 equiv), 2a (2.0 equiv), Et3N·3HF (5 M),
Ru(bpy)3Cl2·6H2O (2 mol %), and Cu(OAc)2 (2 mol %) in 2 mL of
DCE at rt under a nitrogen atmosphere upon blue LED irradiation.
Isolated yield. Yield in the parentheses is for a 2 mmol reaction.
CuF2 was used in place of Cu(OAc)2.
h
10
11
gi
,
a
b
c
1a (0.5 mmol, 1.0 equiv), 2a (2.0 equiv), Et3N·3HF (2.5 M),
d
Ru(bpy)3Cl2·6H2O (2 mol %), and additive (10 mol %) in DCE (2
mL) at rt under a nitrogen atmosphere upon 18 W blue light
b
irradiation. 1H NMR yield of the product; isolated yield in
withdrawing or -donating groups on the phenyl ring produce
the corresponding carbofluorinated products (3aa−3za) in
moderate to good yields. Substituents such as alkyl groups
(3ba−3ga), methoxyl (3ha), esters (3ka and 3la), halides
(3ma−3ra), carboxyl (3sa), and chloromethyl (3ta) are all
tolerated under the carbofluorination reaction conditions.
Notably, substrates with a substituent at the ortho-position of
the phenyl ring give the corresponding products (3ea, 3fa, and
3qa) in moderate yields. The 1,1-disubstitued olefin (1u) can
be converted into the fluorinated product (3ua) in moderate
yield. Furthermore, the reaction scope can be extended to 1,2-
disubstituted olefins. Although the substrate 1v delivers the
corresponding product (3va) in a low yield, methyl cinnamate
affords the desired product (3wa) in moderate yield. 5-
Vinylthiazole (1x), with its heteroaromatic ring, delivers the
carbofluorinated product (3xa) in moderate yield. Conjugated
enynes are also suitable substrates for this reaction, affording
c
parentheses. Another fluoride source, such as CsF (5 equiv), AgF2
(5 equiv), Py·HF (5 equiv), NH4F (5 equiv), or Bu4NF (5 equiv),
d
was used in place of Et3N·3HF. CuF2 (5 equiv) was used without
e
f
Et3N·3HF. 0.5 M Et3N·3HF was used. 1.25 M Et3N·3HF was used.
g
h
5 M Et3N·3HF was used. Without Ru(bpy)3Cl2·6H2O or light.
Cu(OAc)2 (2 mol %) were used.
i
desired fluorinated product (3aa) is obtained in this case in
40% yield, as determined by 1H NMR (Table 1, entry 1). The
yield is improved to 72% yield when Cu(OAc)2 is added to the
reaction mixture (Table 1, entry 2).16 Other copper salts, such
as CuF2 and CuTC, can be used as the additive with which to
promote the reaction (Table 1, entries 3 and 4). When another
fluoride source, such as CsF, AgF2, Py·HF, NH4F, or Bu4NF, is
used in place of Et3N·3HF, no desired product is detected
(Table 1, entry 5). With CuF2 as both the additive and fluoride
sources, the reaction does not deliver the corresponding
B
DOI: 10.1021/acs.orglett.8b01658
Org. Lett. XXXX, XXX, XXX−XXX

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Letter
the alkyl-fluorinated products with an internal C−C triple
bond (3ya and 3za).
Scheme 3. Preliminary Mechanistic Studies
The substrate scope of alkyl diacyl peroxides in the olefin
carbofluorination was studied (Table 3). As reported
a b
,
Table 3. Substrate Scope with Alkyl Diacyl Peroxides
product 8 in a 54% isolated yield through a ring-opening
process of the cyclopropane ring (Scheme 3b). These results
demonstrate that the reaction might involve a free radical
process. To gain further understanding of this free radical
process, methanol was added to the reaction mixture. The
desired product (3aa) is formed in 35% yield (Scheme 3c), but
in addition, the etherification product (9) is isolated in 15%
yield, suggesting that the reaction might involve a benzyl
carbocation intermediate.20
The results of a light ON/OFF experiment (see the
Supporting Information (SI) for details) suggests that the
radicals are generated via a photolytic pathway.21 Further, to
identify which species can quench the excited ruthenium
catalyst, a series of controlled experiments were conducted
(see SI).22 The emission intensity of the excited ruthenium
catalyst decreases slightly with increasing concentration of
LPO or styrene, showing a weak quenching effect. Interesting,
the addition of Cu(OAc)2 to the excited ruthenium catalyst
resulted in a strongly enhanced quenching effect, indicating
that a quenching of the excited ruthenium catalyst by
Cu(OAc)2 is involved in the mechanism. Furthermore,
mechanistic studies reveal that LPO can be fully decomposed
by a stoichiometric amount of Cu(I) species in the dark, but
most of LPO still remains when a stoichiometric amount of
Cu(II) species is employed even under blue light irradiation.23
The experimental results imply that a Cu(I) species might be
related to the LPO cleavage in the catalytic cycle.24
a
1a (0.5 mmol, 1.0 equiv), 2 (2.0 equiv), Et3N·3HF (5 M),
Ru(bpy)3Cl2·6H2O (2 mol %), and Cu(OAc)2 (2 mol %) in 2 mL of
DCE at rt under a nitrogen atmosphere upon blue LED irradiation.
b
Isolated yield.
previously, the alkyl diacyl peroxides can be easily synthesized
from alkyl carboxylic acids.17 Simple primary alkyl substituted
diacyl peroxides afford the corresponding alkyl-fluorinated
products with good yields (3ab−3ah). Primary alkyl groups
with additional functional groups such as phenyl (3ai and 3aj),
chloro (3ak), bromo (3al), alkenyl (3am), or ester (3an) are
well tolerated under the reaction conditions, affording the
corresponding alkyl-fluorinated products in moderate to high
yields. The reactions with secondary alkyl diacyl peroxides
afford low yields, because primary alkyl diacyl peroxides are
relatively more stable and accessible than secondary alkyl
diacyl peroxides and tertiary alkyl diacyl peroxides.
This methodology can be utilized in late-stage functionaliza-
tion of natural product derivatives (Scheme 2). For instance,
Scheme 2. Synthetic Applications of the Olefin
Carbofluorination Method
Because the Cu(II) additive plays an important role in this
olefin carbofluorination, a copper-involved, plausible mecha-
nism for the visible-light induced alkyl-fluorination of olefin via
an oxidative quenching process is proposed and is depicted in
Scheme 4. Visible light irradiation of [Ru(bpy)3]2+ will
generate the excited state complex *[Ru(bpy)3]2+, which
then engages in a single-electron transfer with a Cu(II) species
Scheme 4. Proposed Reaction Mechanism for the
Photoredox Catalyzed Olefin Carbofluorination
the vinyl compounds 4a and 4b, synthesized from estrone,18
were applied in the reaction with LPO and Et3N·3HF under
the standard reaction conditions. The desired alkyl-fluorinated
products (5a and 5b) are synthesized with acceptable
efficiency.
To gain an understanding of the mechanism of the reaction,
a radical trapping experiment was conducted with 2,2,6,6-
tetramethyl-1-piperidinyloxy (TEMPO) as a radical-trapping
reagent.19 In this case, GC-MS analysis fails to detect the
desired product (3aa), but the alkylated-TEMPO compound
(6) can be isolated in 65% yield (Scheme 3a). The
photocatalytic reaction of compound 7 produces the linear
C
DOI: 10.1021/acs.orglett.8b01658
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Letter
to generate a Cu(I) species and an oxidized [Ru(bpy)3]3+
complex.25 Based on the above-mentioned copper(I)-triggered
LPO cleavage, the Cu(I) species engages in a single-electron
transfer with alkyl diacyl peroxide to afford the alkyl free
radical (A), the alkyl carboxylic acid anion, carbon dioxide and
the regenerated Cu(II) species. The alkyl radical A reacts with
2014, 47, 1513−1522. (f) Liang, T.; Neumann, C. N.; Ritter, T.
Angew. Chem., Int. Ed. 2013, 52, 8214−8264.
(2) For selected reviews and books on the application of fluorine
̈
chemistry: (a) Muller, K.; Faeh, C.; Diederich, F. Science 2007, 317,
1881−1886. (b) Purser, S.; Moore, P. R.; Swallow, S.; Gouverneur, V.
́
́
Chem. Soc. Rev. 2008, 37, 320−330. (c) Wang, J.; Sanchez-Rosello,
M.; Acena, J. L.; Pozo, C.; Sorochinsky, A. E.; Fustero, S.;
̃
ox
an olefin to deliver the benzyl free radical (B) [E1/2 = +0.37
Soloshonok, V. A.; Liu, H. Chem. Rev. 2014, 114, 2432−2506.
(d) Richardson, P. Expert Opin. Drug Discovery 2016, 11, 983−999.
(e) Begue, J.-P.; Bonnet-Delpon, D. Bioorganic and Medicinal
Chemistry of Fluorine; John Wiley & Sons: Hoboken, NJ, 2008.
(f) Ojima, I. Fluorine in Medicinal Chemistry and Chemical Biology;
V vs SCE for Ph(CH3)HC•],26 which can be oxidized by the
Ru(III)/Ru(II)
Ru(III) species [E1/2
= +1.29 V vs SCE]27 to form
́
́
the benzyl carbocation (C) and the regenerated Ru(II) species.
Trapped by the nucleophilic fluoride ion, intermediate C
produces the carbofluorinated product.
Wiley-Blackwell: Oxford, 2009. (g) Gouverneur, V.; Muller, K.
̈
Fluorine in Pharmaceutical and Medicinal Chemistry: From Biophysical
Aspects to Clinical Applications; Imperial College Press: London, 2012.
(3) For a review on olefin fluorofunctionalization: Xu, X.-H.; Qing,
F.-L. Curr. Org. Chem. 2015, 19, 1566−1578.
In conclusion, we have developed a photoredox-catalyzed
alkyl-fluorination of olefins under mild reaction conditions.
This highly desirable carbofluorination reaction has a wide
substrate scope and good functional group tolerance. The
nucleophilic fluoride is used instead of the highly valent
electrophilic “F+” ion as the fluorine source in the reaction.
Generic alkyl groups, originating from alkyl carboxylic acids,
are applied to the olefin carbofluorination for the first time as
the alkyl source. Based on these results, a copper-assisted
oxidative quenching mechanism has been proposed for this
Ru-catalyzed olefin carbofluorination.
(4) For selected recent papers on olefin carbofluorination. For olefin
aryl-fluorination: (a) Talbot, E. P. A.; Fernandes, T.; de, A.;
McKenna, J. M.; Toste, F. D. J. Am. Chem. Soc. 2014, 136, 4101−
4104. (b) Wolstenhulme, J. R.; Rosenqvist, J.; Lozano, O.; Ilupeju, J.;
Wurz, N.; Engle, K. M.; Pidgeon, G. W.; Moore, P. R.; Sandford, G.;
Gouverneur, V. Angew. Chem., Int. Ed. 2013, 52, 9796−9800.
(c) Chen, Z.-M.; Yang, B.-M.; Chen, Z.-H.; Zhang, Q.-W.; Wang,
M.; Tu, Y.-Q. Chem. - Eur. J. 2012, 18, 12950−12954. (d) Kindt, S.;
Heinrich, M. R. Chem. - Eur. J. 2014, 20, 15344−15348. (e) Guo, R.;
Yang, H.; Tang, P. Chem. Commun. 2015, 51, 8829−8832. (f) Yang,
B.; Chansaenpak, K.; Wu, H.; Zhu, L.; Wang, M.; Li, Z.; Lu, H. Chem.
Commun. 2017, 53, 3497−3500. For olefin cyano-fluorination:
(g) Dilman, A. D.; Belyakov, P. A.; Struchkova, M. I.; Arkhipov, D. E.;
Korlyukov, A. A.; Tartakovsky, V. A. J. Org. Chem. 2010, 75, 5367−
5370. For olefin oxycarbonyl-fluorination: (h) Qi, X.; Yu, F.; Chen,
P.; Liu, G. Angew. Chem., Int. Ed. 2017, 56, 12692−12696. For olefin
acyl-fluorination: (i) Wang, H.; Guo, L.-N.; Duan, X.-H. Chem.
Commun. 2014, 50, 7382−7384. For olefin trifluoromethyl-
fluorination: (j) Yu, W.; Xu, X.-H.; Qing, F.-L. Adv. Synth. Catal.
2015, 357, 2039−2044. For olefin oxycarbonylmethyl-fluorination:
(k) Zhu, L.; Chen, H.; Wang, Z.; Li, C. Org. Chem. Front. 2014, 1,
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b01658.
Experimental procedures, mechanistic experiments, and
spectroscopic data (PDF)
AUTHOR INFORMATION
Corresponding Authors
■
́
1299−1305. (l) Yuan, W.; Szabo, K. J. Angew. Chem., Int. Ed. 2015,
54, 8533−8537. (m) Chen, H.; Zhu, L.; Li, C. Org. Chem. Front.
2017, 4, 565−568. For intramolecular alkyl migration assisted olefin
*E-mail: hlbao@fjirsm.ac.cn.
*E-mail: liyajun@fjirsm.ac.cn.
ORCID
́
́
alkyl-fluorination: (n) Romanov-Michailidis, F.; Guenee, L.; Alexakis,
A. Angew. Chem., Int. Ed. 2013, 52, 9266−9270. (o) Zhao, H.; Fan, X.;
Yu, J.; Zhu, C. J. Am. Chem. Soc. 2015, 137, 3490−3493.
Yajun Li: 0000-0001-6690-2662
Hongli Bao: 0000-0003-1030-5089
Notes
́
(5) For selected reviews: (a) Nyffeler, P. T.; Duron, S. G.; Burkart,
M. D.; Vincent, S. P.; Wong, C.-H. Angew. Chem., Int. Ed. 2005, 44,
192−212. (b) Badoux, J.; Cahard, D. Org. React. 2007, 69, 347.
(6) For selected papers on nucleophilic fluoride ion: (a) Sun, H.;
DiMagno, S. G. J. Am. Chem. Soc. 2005, 127, 2050−2051. (b) Grushin,
V. V. Acc. Chem. Res. 2010, 43, 160−171. (c) Watson, D. A.; Su, M.;
Teverovskiy, G.; Zhang, Y.; García-Fortanet, J.; Kinzel, T.; Buchwald,
S. L. Science 2009, 325, 1661−1664. (d) Lu, D.-F.; Zhu, C.-L.; Sears,
J. D.; Xu, H. J. Am. Chem. Soc. 2016, 138, 11360−11367.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the National Key R&D Program of China (Grant
No. 2017YFA0700100), the NSFC (Grant No. 21502191,
21672213), the Strategic Priority Research Program of the
Chinese Academy of Sciences (Grant No. XDB20000000), the
Haixi Institute of CAS (Grant No. CXZX-2017-P01), “the
1000 Youth Talents Program”, and the Natural Science
Foundation of Fujian Province (Grant No. 2018J05037) for
financial support.
(7) There are few examples on alkyl-fluorinations of conjugate
olefins with electrophilic “F+” ion: (a) Huang, Y.; Walji, A. M.; Larsen,
C. H.; MacMillan, D. W. C. J. Am. Chem. Soc. 2005, 127, 15051−
15053. (b) Quintard, A.; Alexakis, A. Adv. Synth. Catal. 2010, 352,
1856−1860. (c) Wang, L.; Meng, W.; Zhu, C.-L.; Zheng, Y.; Nie, J.;
Ma, J.-A. Angew. Chem., Int. Ed. 2011, 50, 9442−9446. During the
preparation of this manuscript, a paper on trifluoromethyl- and
trichloromethyl-fluorination of unactivated alkenes with fluoride ions
was reported: (d) Liu, Z.; Chen, H.; Lv, Y.; Tan, X.; Shen, H.; Yu, H.-
Z.; Li, C. J. Am. Chem. Soc. 2018, 140, 6169−6175.
(8) Other selected methods for the synthesis of benzylic fluoride.
Benzylic C−H fluorination: (a) Hua, A. M.; Mai, D. N.; Martinez, R.;
Baxter, R. D. Org. Lett. 2017, 19, 2949−2952. (b) Zhang, Q.; Yin, X.-
S.; Chen, K.; Zhang, S.-Q.; Shi, B.-F. J. Am. Chem. Soc. 2015, 137,
8219−8226. (c) Nodwell, M. B.; Bagai, A.; Halperin, S. D.; Martin, R.
E.; Knust, H.; Britton, R. Chem. Commun. 2015, 51, 11783−11786.
REFERENCES
■
(1) For selected reviews on incorporation of fluorine into organic
molecules: (a) Yang, X.; Wu, T.; Phipps, R. J.; Toste, F. D. Chem. Rev.
2015, 115, 826−870. (b) Ni, C.; Zhu, L.; Hu, J. Huaxue Xuebao 2015,
73, 90−115. (c) Champagne, P. A.; Desroches, J.; Hamel, J. D.;
Vandamme, M.; Paquin, J. F. Chem. Rev. 2015, 115, 9073−9174.
(d) Alonso, C.; de Marigorta, E. M.; Rubiales, G.; Palacios, F. Chem.
Rev. 2015, 115, 1847−1935. (e) Chu, L.; Qing, F.-L. Acc. Chem. Res.
D
DOI: 10.1021/acs.orglett.8b01658
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(d) Bloom, S.; Pitts, C. R.; Woltornist, R.; Griswold, A.; Holl, M. G.;
Lectka, T. Org. Lett. 2013, 15, 1722−1724. (e) Liu, W.; Groves, J. T.
Angew. Chem., Int. Ed. 2013, 52, 6024−6027. (f) Xia, J.-B.; Zhu, C.;
Chen, C. J. Am. Chem. Soc. 2013, 135, 17494−17500. Other recent
methods for the synthesis of benzylic fluorides: (g) Banik, S. M.;
Mennie, K. M.; Jacobsen, E. N. J. Am. Chem. Soc. 2017, 139, 9152−
9155. (h) Sheng, J.; Ni, H.-Q.; Liu, G.; Li, Y.; Wang, X.-S. Org. Lett.
2017, 19, 4480−4483. (i) Pitts, C. R.; Ling, B.; Snyder, J. A.; Bragg, A.
E.; Lectka, T. J. Am. Chem. Soc. 2016, 138, 6598−6609. (j) Yuan, Z.;
Wang, H.-Y.; Mu, X.; Chen, P.; Guo, Y.-L.; Liu, G. J. Am. Chem. Soc.
2015, 137, 2468−2471. (k) Huang, X.; Liu, W.; Hooker, J. M.;
Groves, J. T. Angew. Chem., Int. Ed. 2015, 54, 5241−5245.
DCE (2 mL) at rt under a nitrogen atmosphere upon 18 W blue light
irradiation.
(25) The reductive potential of Cu(II) (+0.16 V vs NHE) is much
more positive than that of *Ru(II) (−0.84 V vs SCE). (a) Lange, N.
A. In Lange’s Handbook of Chemistry, 15th ed.; Dean, J. A., Ed.;
McGraw-Hill: New York, NY, 1999; Section 8. (b) Campagna, S.;
Puntoriero, F.; Nastasi, F.; Bergamini, G.; Balzani, V. Top. Curr. Chem.
2007, 280, 117−214.
(26) Wayner, D. D. M.; McPhee, D. J.; Griller, D. J. Am. Chem. Soc.
1988, 110, 132−137.
(27) (a) Chatterjee, T.; Iqbal, N.; You, Y.; Cho, E. J. Acc. Chem. Res.
2016, 49, 2284−2294. (b) Carboni, A.; Dagousset, G.; Magnier, E.;
Masson, G. Org. Lett. 2014, 16, 1240−1243. (c) Lin, R.; Sun, H.;
Yang, C.; Xia, W. Asian J. Org. Chem. 2017, 6, 418−421.
(9) (a) Clark, A. J. Chem. Soc. Rev. 2002, 31, 1−11. (b) Reiser, O.
Acc. Chem. Res. 2016, 49, 1990−1996.
(10) Light-induced olefin hydrofluorination: Wilger, D. J.;
Grandjean, J.-M. M.; Lammert, T. R.; Nicewicz, D. A. Nat. Chem.
2014, 6, 720−726.
(11) For another example on light-induced olefin aryl-fluorination:
Chan, M. S. W.; Arnold, D. R. Can. J. Chem. 1997, 75, 1810−1819.
(12) For reviews on oxidative alkyl reagents: (a) Xuan, J.; Zhang, Z.-
G.; Xiao, W.-J. Angew. Chem., Int. Ed. 2015, 54, 15632−15641.
(b) Patra, T.; Maiti, D. Chem. - Eur. J. 2017, 23, 7382−7401. (c) Li,
Y.; Ge, L.; Muhammad, M. T.; Bao, H. Synthesis 2017, 49, 5263−
5284. For selected papers on oxidative alkyl reagents: (d) Wang, Y.;
Zhang, L.; Yang, Y.; Zhang, P.; Du, Z.; Wang, C. J. Am. Chem. Soc.
2013, 135, 18048−18051. (e) Yoshida, M.; Morinaga, Y.; Iyoda, M. J.
Fluorine Chem. 1994, 68, 33−38. (f) Yoshida, M.; Moriya, K.; Sawada,
H.; Kobayashi, M. Chem. Lett. 1985, 14, 755−758.
(13) For reviews on visible-light induced difunctionalization of
olefin: (a) Prier, C. K.; Rankic, D. A.; MacMillan, D. W. C. Chem. Rev.
̈
2013, 113, 5322. (b) Ghosh, I.; Marzo, L.; Das, A.; Shaikh, R.; Konig,
B. Acc. Chem. Res. 2016, 49, 1566−1577. (c) Koike, T.; Akita, M. Acc.
Chem. Res. 2016, 49, 1937−1945. (d) Staveness, D.; Bosque, I.;
Stephenson, C. R. J. Acc. Chem. Res. 2016, 49, 2295−2306.
(14) For an excellent paper discussing oxidative and reductive
quenching of photocatalysts: Wallentin, C.-J.; Nguyen, J. D.;
Finkbeiner, P.; Stephenson, C. R. J. J. Am. Chem. Soc. 2012, 134,
8875−8884.
(15) (a) Lackner, G. L.; Quasdorf, K. W.; Overman, L. E. J. Am.
Chem. Soc. 2013, 135, 15342−15345. (b) Ge, L.; Li, Y.; Jian, W.; Bao,
H. Chem. - Eur. J. 2017, 23, 11767−11770.
(16) There are few papers discussing the interaction of a copper salt
and ruthenium-based photocatalyst: (a) Ye, Y.; Sanford, M. S. J. Am.
Chem. Soc. 2012, 134, 9034−9037. (b) Rueping, M.; Koenigs, R. M.;
Poscharny, K.; Fabry, D. C.; Leonori, D.; Vila, C. Chem. - Eur. J. 2012,
18, 5170−5174. (c) Iali, W.; Lanoe, P.-H.; Torelli, S.; Jouvenot, D.;
́
Loiseau, F.; Lebrun, C.; Hamelin, O.; Menage, S. A. Angew. Chem., Int.
Ed. 2015, 54, 8415−8419.
(17) (a) Li, Y.; Han, Y.; Xiong, H.; Zhu, N.; Qian, B.; Ye, C.;
Kantchev, E. A. B.; Bao, H. Org. Lett. 2016, 18, 392−395. (b) Qian,
B.; Chen, S.; Wang, T.; Zhang, X.; Bao, H. J. Am. Chem. Soc. 2017,
139, 13076−13082.
́
(18) Shu, W.; Lorente, A.; Gomez-Bengoa, E.; Nevado, C. Nat.
Commun. 2017, 8, 13832.
(19) (a) Moad, G.; Rizzardo, E.; Solomon, D. H. Aust. J. Chem.
1983, 36, 1573−1588. (b) Zhu, X.; Ye, C.; Li, Y.; Bao, H. Chem. - Eur.
J. 2017, 23, 10254−10258.
(20) Wang, F.; Wang, D.; Mu, X.; Chen, P.; Liu, G. J. Am. Chem. Soc.
2014, 136, 10202−10205.
(21) Cismesia, M. A.; Yoon, T. P. Chem. Sci. 2015, 6, 5426−5434.
(22) Geng, X.; Lin, F.; Wang, X.; Jiao, N. Org. Lett. 2017, 19, 4738−
4741.
(23) LPO was fully decomposed in the presence of 1.2 equiv of
Cu(OAc) in a DCE solution in the dark under a nitrogen atmosphere
for 24 h. But, in the presence of 1.2 equiv of Cu(OAc)2, most of the
LPO remained even irradiated under blue LEDs for 24 h.
(24) The alkyl-fluorination of olefins failed when CuTC/bpy was
used as the catalysis system: styrene (0.5 mmol, 1.0 equiv), LPO (2.0
equiv), Et3N·3HF (5 M), CuTC (7 mol %), and bpy (14 mol %) in
E
DOI: 10.1021/acs.orglett.8b01658
Org. Lett. XXXX, XXX, XXX−XXX