Visible-Light-Induced Selective Defluoroborylation of Polyfluoroarenes, gem-Difluoroalkenes, and Trifluoromethylalkenes

Article abstract of DOI:10.1002/anie.201911819

Fluorinated organoboranes serve as versatile synthetic precursors for the preparation of value-added fluorinated organic compounds. Recent progress has been mainly focused on the transition-metal catalyzed defluoroborylation. Herein, we report a photocatalytic defluoroborylation platform through direct B?H activation of N-heterocyclic carbene boranes, through the synergistic merger of a photoredox catalyst and a hydrogen atom transfer catalyst. This atom-economic and operationally simple protocol has enabled defluoroborylation of an extremely broad scope of multifluorinated substrates including polyfluoroarenes, gem-difluoroalkenes, and trifluoromethylalkenes in a highly selective fashion. Intriguingly, the defluoroborylation protocol can be transition-metal free, and the regioselectivity obtained is complementary to the reported transition-metal-catalysis in many cases.

Full text of DOI:10.1002/anie.201911819

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
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International Edition
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Accepted Article
Title: Visible-Light-Induced Selective Defluoroborylation
of Polyfluoroarenes, gem-Difluoroalkenes, and
Trifluoromethylalkenes
Authors: Wengang Xu, Heming Jiang, Jing Leng, Han-Wee Ong, and
Jie Wu
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201911819
Angew. Chem. 10.1002/ange.201911819
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10.1002/anie.201911819
Angewandte Chemie International Edition
RESEARCH ARTICLE
Visible-Light-Induced Selective Defluoroborylation of
Polyfluoroarenes, gem-Difluoroalkenes, and
Trifluoromethylalkenes
Wengang Xu, Heming Jiang, Jing Leng, Han-Wee Ong, and Jie Wu*
Abstract: Fluorinated organoboranes serve as versatile synthetic
precursors for the preparation of value-added fluorinated organic
compounds. Recent progress has been mainly focused on the
transition-metal catalyzed defluoroborylation. Herein, we report a
photocatalytic defluoroborylation platform via direct B−H activation of
N-heterocyclic carbene boranes, through the synergistic merger of a
photoredox catalyst and a hydrogen atom transfer catalyst. This atom-
economic and operationally simple protocol has enabled
defluoroborylation of an extremely broad scope of multifluorinated
substrates including polyfluoroarenes, gem-difluoroalkenes, and
trifluoromethylalkenes in a highly selective fashion. Intriguingly, the
defluoroborylation protocol can be transition-metal free, and the
regioselectivity obtained is complementary to the reported transition-
metal-catalysis in many cases.
distinct organic fluorides through a wide spectrum of established
and reliable derivatization reactions.[8] The most straightforward
way to access fluorinated organic borane building blocks is
selective C–F bond borylation of polyfluorinated organic
compounds. However, this is inherently challenging for several
reasons: 1) the C–F bond is among the most unreactive functional
groups; 2) the high bond energy of metal-fluorine intermediates
can lead to sluggish catalytic turnover in transition-metal-
catalyzed C–F activation; and 3) boron reagents are fluorophilic
and serve as fluorine scavengers in C–F derivatization.
Introduction
Approximately 20% of all pharmaceuticals and 30% of all
agrochemicals contain carbon–fluorine bonds.[1] There is
currently an increasing demand for introduction of fluorinated
building blocks into organic frameworks, and compounds of this
sort have found a wide range of applications in the development
of novel pharmaceutical agents,[2] insecticides,[3] catalysts,[4] and
materials.[5] However, fluoroaromatic and vinyl fluoride
compounds do not exist naturally and must be synthesized.[6]
Despite spectacular advances in single-site catalytic fluorination,
synthetic access to polyfluorinated compounds in a selective
fashion is still challenging.[7] In this context, fluorinated organic
boranes can serve as versatile synthetic precursors to obtain
[*]
Dr. W. Xu, J. Leng, H.-W Ong, Dr. J. Wu
Department of Chemistry, National University of Singapore
3 Science Drive 3, Singapore 117543, Republic of Singapore
E-mail: chmjie@nus.edu.sg
H. Jiang
Laboratory of Computational Chemistry & Drug Design, State Key
Laboratory of Chemical Oncogenomics, Peking University
Shenzhen Graduate School, Shenzhen, 518055, People’s Republic
of China
J. Leng
State Key Laboratory of Silicate Materials for Architectures, Wuhan
University of Technology, 122 Luoshi Road, Wuhan, Hubei, 430070,
People’s Republic of China
Dr. W. Xu
Scheme 1. C–F bond activation of fluoroarenes and alkenes. TM = transition-
metal catalyst; pinB-Bpin = bis(pinacolato)diboron; PC = photocatalyst; HAT =
hydrogen atom transfer; LED = light-emitting diode.
College of New Energy, Institute of New Energy, State Key
Laboratory of Heavy Oil Processing, China University of Petroleum
(East China), Qingdao, 266580, People’s Republic of China
Dr. J. Wu
National University of Singapore (Suzhou) Research Institute, 377
Lin Quan Street, Suzhou Industrial Park, Suzhou, Jiangsu, 215123,
People’s Republic of China
Most success in catalytic defluoroborylation thus far has relied
on catalysis by transition-metal, including Rh,[9] Ni,[10] Cu[11], Co[12]
and Fe-based[13] catalysis (Scheme 1a). However, higher
temperatures are generally required in these reactions, and
Supporting information for this article is given via a link at the end of
the document. CCDC 1894872 and 1937072.
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10.1002/anie.201911819
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RESEARCH ARTICLE
stoichiometric metallic additives are often employed to scavenge
the fluoride ions generated in situ. Photocatalysis has witnessed
dramatic developments over the past decade which have enabled
previously inaccessible synthetic transformations.[14] In particular,
photolytically-induced borylation of C–F bonds in electron-rich
monofluoroarenes has been realized by Li[15] and by Larionov[16]
though the formation of triplet aryl cations by the heterolysis of
C(sp2)–F bonds using strong ultraviolet (UV) light. Very recently,
the group of Guo, Radius, Steffen, and Marder demonstrated a
visible-light-promoted C–F borylation protocol that employs a Rh
photosensitizer to accelerate the difficult transmetalation step in
the nickel-catalyzed C–F activation.[17]
Polyfluorinated arenes and alkenes have been applied to C–C
bond formation via photocatalytic C–F bond functionalization.
Weaver et al. have achieved a variety of C–C couplings of
perfluoroarenes with alkenes, alkynes, arenes, and prenyl
reagents by photoredox catalysis.[18] This coupling was initiated
by polyfluoroaryl radicals generated through light-promoted single
electron reduction of polyfluoroarenes followed by extrusion of
fluoride (Scheme 1b). Remarkably, Xie, Hashmi and co-workers
recently demonstrated a photo-mediated mono-defluoroalkylation
of gem-difluoroalkenes using N-aryl amines by a radical-radical
coupling pathway.[19a] They subsequently expanded the scope to
polyfluoroarenes for controllable defluoroalkylation (Scheme
1b).[19b] The Molander group achieved a fascinating synthesis of
gem-difluoroalkene moieties by photoredox-induced carbon
radical addition to -trifluoromethylalkenes.[20]
On the other hand, the development of boron-centered radical
chemistry has recently gained increasing momentum, and is
conceptually appealing because it may offer regio- or
stereoselectivities different from those of transition-metal-
catalysis.[21] Elegant work from Fensterbank, Lacôte, Malacria,
and Curran has shown that N-heterocyclic carbene (NHC)-boryl
radicals can be generated by hydrogen atom abstraction from
NHC-BH3 complexes,[21a,22] which are powerful intermediates
useful in building a wide range of value-added boron compounds.
For instance, Wang has developed radical borylation/cyclization
cascade of 1,6-enynes with NHC-BH3,[21c] and Curran and
Taniguchi reported the Sato-Myers cyclization triggered by NHC-
boryl radicals.[22d] Consistent with our continuing interest in
entry
1
deviation
none
Yield of 3a[a]
94[b]
2
Ir[dF(CF3)ppy]2(dtbbpy)PF6 (2.0 mol%)
Ir(ppy)3 instead of PC1
93
0
3
4
Ir(ppy)2(dtbbpy)PF6 instead of PC1
Ir(dFppy)2(dtbbpy)PF6 instead of PC1
4CzIPN (2 mol%) instead of PC1
4CzIPN (2 mol%) instead of PC1
without light or PC1
88
87
76
90
0
5
6
7[c]
8
9
without S1
16
68
10
without base
Reaction conditions: hexafluorobenzene (1a, 0.20 mmol), NHC-
borane (2a, 0.24 mmol), Ir[dF(CF3)ppy]2(dtbbpy)PF6 (PC1, 1
mol%), S1 (10 mol%), NaOAc (0.10 mmol), THF (4 mL), 18W blue
LED irradiation, room temperature, 12 h. [a] Yields were
determined by analysis of the crude 1H NMR spectra using 1,3,5-
trimethoxybenzene as an internal standard. [b] Isolated yields. [c]
S2 was used instead of S1. THF = tetrahydrofuran.
development
of
atom-economic
and
redox-neutral
transformations through hydrogen atom transfer (HAT)-based
photocatalysis,[23] we envisioned that a photo-mediated catalytic
HAT process with NHC-BH3 might deliver the boryl radical in a
mild pathway, which could react with polyfluoroarenes and
alkenes to introduce synthetically valuable fluorinated organic
boranes (Scheme 1c). Notably, Lacôte and Lalevée developed
visible-light induced NHC-boryl radical formation through a HAT
process with thiyl radicals.[22c] During the course of our
investigation, the group of Xie and Zhu has reported an elegant
study on photocatalytic version of this reaction to realize the
inverse hydroboration of imines.[24]
Our investigation was initiated with examination of the
defluoroborylation of hexafluorobenzene (1a) with NHC-borane
2a as the model substrates in the presence of a photoredox
catalyst and a HAT catalyst under blue LED irradiation. After
extensive evaluation (Table 1 and Table S1), we established that
a combination of Ir[dF(CF3)ppy]2(dtbbpy)PF6 (PC1) (1 mol%), thiol
(S1) (10 mol%), and NaOAc (0.5 equiv) in THF (0.05 M) at
ambient temperature was optimal and produced the desired
defluoroborylation product (3a) in 94% isolated yield (Table 1,
entry 1). Increasing the catalyst loading to 2 mol% gave a similar
yield (entry 2). Ir(ppy)3, which was previously employed in
Weaver’s photocatalytic hydrodefluorination,[25] showed no
catalytic activity in the defluoroborylation (entry 3). Other Ir
Results and Discussion
photocatalysts,
such
as
Ir(ppy)2(dtbbpy)PF6
and
Ir(dFppy)2(dtbbpy)PF6 exhibited much lower efficiency (entries 4
and 5). Moderate yield could be obtained by using the organic dye,
2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) as the
Table 1. Condition optimization for photo-mediated defluoroborylation of
polyfluoroarenes
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Scheme 2. Scope of photo-mediated selective defluoroborylation of polyfluoroarenes.[a] [a] All isolated yields. Product was produced as a single regioisomer unless
otherwise noted. Condition A was employed unless otherwise noted. [b] Condition B was employed. [c] 2a (2.4 equiv) was used.
With the optimal photo-induced defluoroborylation conditions in
hand, we explored the substrate scope using the Ir photocatalyst-
based protocol (Condition A) or the transition-metal-free protocol
photocatalyst, which possesses redox properties similar to those
of PC1 (entry 6).[26] The yield can be improved to 90% by replacing
the thiol HAT catalyst S1 with S2, enabling an effective transition-
metal-free photocatalytic defluoroborylation protocol (entry 7).
Control experiments demonstrated that light, photocatalyst, thiol
and base were all essential for efficient defluoroborylation (entries
8-10).
(Condition B) (Scheme 2).
A series of pentafluoroarene
derivatives underwent regioselective defluoroborylation efficiently
(1b-1l). Notably, the transition-metal-free protocol (Condition B)
afforded products (3b-3e) in yields comparable to those obtained
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RESEARCH ARTICLE
with the Ir protocol (Condition A), demonstrating a practical
strategy to prepare fluorinated organic boranes in a transition-
metal-free manner. Functionalities such as a trifluoromethyl group
(3e), ketone (3g), ester (3h), boronic ester (3i), pyridine (3j), and
phosphine (3k, 3l) were well-tolerated. Diborylation could be
selectively achieved in good yields using 2.4 equivalents of NHC-
observed,[9c,10b,17] providing an orthogonal strategy for
regioselective defluoroborylation of polyfluoroarenes.
borane
(3d’,
3l’).
1,2,3,4-Tetrafluorobenzene
was
defluoroborylated in excellent regioselectivity to deliver product
3m in 85% yield. Tetrafluorobenzenes bearing functional groups
such as aryl bromides and benzyl ethers also participated in the
defluoroborylation to afford 3n and 3o in 45% and 53% yield
respectively. Tetrafluorobenzenes containing an amine
substituent underwent defluoroborylation selectively at the ortho-
position to the amino group (3p-3r). The regioselectivity was
confirmed by crystallographic analysis of the product 3q.[27]
Defluoroborylation of ester-substituted tetrafluoroarenes occurred
exclusively at the position ortho to the ester group (3s).
Importantly, the substrate scope could be successfully expanded
to trifluoroarenes and even difluoroarenes substituted with
electron-deficient functionalities such as ketone (3u), ester (3v-
3x), and nitrile (3z and 3ab) in a highly selective fashion.
Surprisingly,
hydroborylation
occurred
to
produce
dearomatization products (4t, 4x, 4y, and 4aa) in good yields as
a single diastereomer if the para-position of an electron-
withdrawing functional group (e.g. ester and nitrile) was
unsubstituted in the polyfluoroarenes. The stereo-configuration of
4y was identified by X-ray crystallographic analysis, illustrating a
trans hydroborylation,[28] and the structures of other
dearomatization products were assigned by analogy. The scope
for NHC-boranes was subsequently evaluated. Various NHC-
boranes more sterically hindered than 2a were good candidates,
giving products 3ac-3ag with 73% to 96% yields.
Scheme 3. Photo-mediated defluoroborylation of gem-difluoroalkenes.[a] [a]
Isolated yields. E/Z ratios were determined by the analysis of 1H NMR spectra.
DIPEA = N,N-diisopropylethylamine.
We subsequently attempted to extend this methodology to
gem-difluoroalkenes, which are readily available building
blocks.[31] The optimal conditions for defluoroborylation of gem-
difluoroalkenes were defined using
a
combination of
[Ir(dF(CF3)ppy)2(5,5’-dFbpy)]PF6,[32] thiol (S2) and DIPEA in THF
at room temperature under blue LED irradiation for 12 h. As
illustrated in Scheme 3, symmetrical gem-difluoroalkenes
participated well to afford mono-fluoroalkenylboranes in moderate
to good yields (6a-6d). In the case of unsymmetrical gem-
difluoroalkenes, mixtures of E/Z isomers (6e-6p) were obtained.
Electron-withdrawing substituents such as chloride (6g) and
bromide (6h), as well as electron-rich substituents including
methyl sulfide (6i), phenol (6j), amine (6k), and methyl ether (6l)
were well-tolerated. meta-Substituted aryl (6l, 6m) and 1- or 2-
naphthyl (6n, 6o) gem-difluoroalkenes delivered the
defluoroborylation products smoothly. A fluoroalkene containing a
The most intriguing part of this method is probably the excellent
regioselectivity for C–F bond activation achieved with
polyfluoroarene substrates. Even though a general prediction
mode cannot be established at the current stage, and may require
sophisticated kinetic studies and computational calculations, the
following trends can be observed and may be instructional with
respect to the other radical-based C–F functionalization of
polyfluoroarenes. 1) Polyfluoroarenes with electron-deficient
substituents are generally more reactive and selective than those
with electron-rich substituents (1e vs 1f). 2) For
pentafluoroarenes, the fluoride substitution took place at the most
electronegative site of the radical anion intermediates derived
from pentafluoroarenes (1b-1l).[29] 3) For tetrafluoroarene (1s)
and trifluoroarene (1u-1x, 1z) with an electron-withdrawing
substituent (e.g. ester, ketone, nitrile), the C–F activation
reactivity trend was ortho > para > meta. 4) In the case of
fluoroarenes containing an amine substituent (1p-1r), the reaction
was directed by intramolecular hydrogen bonding and occurred at
the ortho position of the amine substituent. The hydrogen bond
might facilitate the fragmentation step and direct the
regioselectivity to overcome the innate electronics of the
fluorinated arene substrates.[30] 5) Hydroborylation may occur to
produce dearomatization products if a proton was located at the
para-position of an electron-withdrawing group (1t, 1x, 1y, and
1aa). Notably, in some cases, such as 3c and 3j, the
regioselectivity is different from that obtained with the transition-
metal-catalyzed processes where ortho defluoroborylation was
pyridyl substituent was also
a good candidate for this
transformation (6p).
gem-Difluoroallylboranes are important synthons for
preparation of bioactive fluorinated compounds.[13] We speculated
that the HAT-induced nucleophilic NHC-boryl radical[33] could add
to an α-trifluoromethyl alkene, and a subsequent single electron
reduction [20] would promote an E1cB-type fluoride elimination [34]
to access such boranes. Indeed, after slight modifications of the
photo-induced defluoroborylation protocol, this transformation
was achieved efficiently under the transition-metal free conditions,
with 4-CzIPN as the photocatalyst. The scope of
trifluoromethylalkenes is illustrated in Scheme 4. The reactions
proceeded smoothly with para-, ortho-, and meta-substituted α-
trifluoromethylstyrenes to deliver gem-difluoroallylboranes in
moderate to good yields (8a-8j). Styryl systems bearing a phenyl
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RESEARCH ARTICLE
ether (8c), a trifluoromethyl substituent (8d), a bromide (8e), an
alkene (8f), a fluoride (8g and 8i), and a chloride (8j) were all
effectively transformed into their corresponding gem-
difluoroallylboranes. Naphthyl-substituted trifluoromethyl alkene
also underwent successful defluoroborylation (8k).
Scheme 5. Control experiments to elucidate reaction mechanisms.
Plausible mechanistic pathways for the defluoroborylation were
proposed in light of all the experimental data. As illustrated in
Scheme 4. Photo-mediated defluoroborylation of trifluoromethylalkenes.[a] [a]
Isolated yields.
Scheme 6a, after photoexcitation of Ir(III) catalyst, the Ir(III)*
*III/II
(E1/2
= +1.21 V vs. saturated calomel electrode (SCE))
undergoes a single electron transfer with a thiol (E1/2ox = +0.77 V
vs. SCE) through a proton-coupled electron transfer to produce
an Ir(II) species and thiyl radical I in the presence of base. A
kinetically favored polarity-matched HAT[22] between electrophilic
thiyl radical I and NHC-BH3 (BDE of BH = 72.8 kcal/mol based
on DFT calculations, slightly lower than the previous calculated
value in the range of 74-80 kcal/mol[21a,36]) gives NHC-boryl radical
II and recovers the thiol catalyst (BDE of SH = 76.1 kcal/mol).
The defluoroborylation of polyfluoroarenes and gem-
difluoroalkenes can be achieved by three possible pathways
A series of control experiments were conducted to further
elucidate the reaction mechanism (Scheme 5). No product was
observed in the presence of 2,2,6,6-tetramethyl-1-piperidyloxy
(TEMPO), indicating a radical-based pathway (Scheme 5a).
Stern-Volmer quenching studies illustrated that the thiol can
quench the excited photocatalyst, whereas the polyfluoroarene,
gem-difluoroalkene, and trifluoromethylalkene cannot (see the
Supporting Information). Under similar conditions, the
hydroboration of alkynes proceeded in high efficiency (Scheme
5b), which suggested the presence of boryl radical
intermediates.[21e] Hydrodefluorination could be achieved with the
same photocatalyst (Scheme 5c), indicating that a single electron
reduction of the fluoroarene to fluoroaryl radical anion might
occur.[25] The reaction of hexafluorobenzene with deuterated
borane (2a-D) proceeded efficiently under the standard conditions
to give deuterated product (3a-D) in 90% yield (Scheme 5d). The
kinetic isotope effect (KIE) was determined to be 1.1 by
measuring the initial rates of parallel reactions of 2a and 2a-D with
hexafluorobenzene (see the Supporting Information), which
suggested that the HAT of NHC-borane may not be involved in
the rate-determining step. A radical chain-based mechanism was
unlikely as the measured quantum yield was 0.43.[35]
involving the NHC-boryl radical II and the fluoro substrate. 1) The
III/II
generated Ir(II) species (E1/2
= −1.37 V vs. SCE) can be
oxidized by fluoroarene (E1/2red = −2.38 V vs. SCE for 1a) or gem-
difluoroalkene (E1/2red = −1.04 V vs. SCE for 5a)[19a] to reproduce
the Ir(III) catalyst and a radical anion III. This process is supported
by the control experiment (Scheme 5c) and may be accelerated
by the stabilization induced by the interaction between fluoroaryl
radical anion III and the positively charged Ir(III) catalyst.[19]
Radical recombination occurs between the fluoroaryl radical
anion III and NHC boryl radical II followed by the fluoride
fragmentation to give the desired product 3 or 6. 2) Fluoride
extrusion from radical anion III may occur before the radical
recombination. 3) Direct addition of NHC-boryl radical II to the
fluoroarene or gem-difluoroalkene and subsequent single-
electron reduction by the Ir(II) species, followed by fluoride
extrusion delivers the final product. When a proton is located at
the para-position of an electron-withdrawing group in the
polyfluoroarene, protonation of intermediate IV occurs to generate
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10.1002/anie.201911819
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RESEARCH ARTICLE
the dearomatized hydroborylation product 4 (Scheme 6b), which
may exclude the second possible pathway. Detailed coupling
mechanistic investigations to distinguish between these pathways
and gain a better appreciation of the source of selectivity are
conditions or gem-difluoroallylboronates 15 with pinacol under
acidic conditions.
currently
under
progress
in
our
laboratory.
With
trifluoromethylalkene substrates, the in situ formed NHC-boryl
radical II will undergo radical addition to the alkene followed by a
SET reduction by the reduced state of 4-CzIPN to generate a
carbanion VI.[20] The following E1cB-type fluoride elimination will
provide the gem-difluoroallylborane product 8 (Scheme 6c).
Scheme 7. Further transformations of fluoroarylborane (3a) and gem-
difluoroallylborane (8e)
Conclusion
In summary, we have developed a practical and selective
defluoroborylation of polyfluoroarenes, gem-difluoroalkenes, and
trifluoromethylalkenes in an atom- and redox-economic manner
through photoredox and HAT-induced B–H activation. The
selectivity is generally high, and can be orthogonal to transition-
metal-catalyzed defluoroborylation. Fluorinated organoboranes
with different degrees of fluorination and a wide range of
functionalities were accessed by operationally simple and mild
protocols, even in a transition-metal-free manner, and will likely
find broad applications for the synthesis of value-added
organofluorine compounds.
Scheme 6. Proposed plausible mechanisms.
The synthetic value of this method was further demonstrated by
diversification of the defluoroborylation product 3a and gem-
difluoroallylborane 8e (Scheme 7). (Perfluoro-phenyl)boronic acid
9 was produced in high yield by a simple bromination/hydrolysis
cascade, which has been widely utilized in cross-coupling
reactions to deliver valuable polyfluoroarene compounds.[8]
Treatment of borane 3a with phenyl bromide under palladium-
catalyzed cross-coupling conditions led to mono- (10a) and di-
arylation (10b) of the NHC part of 3a in 17% and 35% yield,
respectively. The mono-defluoroborylation product 3a could
undergo further defluoroborylation to achieve 1,4-diborane
product 11 in good yield. The reaction between 3a and Selectfluor
afforded borane difluoride 12 in high yield, which could act as a
boronic acid equivalent in further diversifications.[37] The borane
difluoride 12 could also undergo further defluoroborylation,
leading to the diborylated compound 13 with two distinguishable
boron substituents. gem-Difluoroallylboranes 8e can be directly
transformed to gem-difluoroallyl alcohol 14 under oxidative
Experimental Section
Typical procedure for defluoroborylation of fluoroarenes: In a 10 mL
Schlenk tube with a magnetic stir bar were placed PC1 (1 mol%) or 4-
CzIPN (2 mol%), NaOAc (8.4 mg, 0.1 mmol, 50 mol%), and NHC-BH3 (2,
0.24 mmol, 1.2 equiv). Under nitrogen atmosphere, fluoroarenes (1, 0.2
mmol, 1 equiv), S1 or S2 (0.02 mmol, 10 mol%), THF (4 mL) were
subsequently added. The resulting mixture was sealed and degassed via
freeze-pump-thaw for three times. Then, the reaction was placed under
blue LED (2-meter strips, 18 W) and irradiated for 12 h at room
temperature. The solvent was removed under vacuum. Silica gel
chromatography (eluent: hexane and ethyl acetate) of the crude product
mixture afforded the desired compound.
Acknowledgements
We appreciate the insightful discussion from Prof. Zhang Xinhao
(Peking University Shenzhen Graduate School) and Prof. Luo
Sanzhong (Tsinghua University). We are grateful for the financial
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[17] Y.-M. Tian, X.-N. Guo, M. W. Kuntze-Fechner, I. Krummenacher, H.
Braunschweig, U. Radius, A. Steffen, T. B. Marder, J. Am. Chem. Soc.
2018, 140, 17612-17623.
support provided by the Ministry of Education (MOE) of Singapore
(MOE2017-T2-2-081), GSK-EDB (R-143-000-687-592), NUS
(Suzhou) Research Institute, and National Natural Science
Foundation of China (Grant No. 21702142, 21871205).
[18] a) A. Singh, J. J. Kubik, J. D. Weaver, Chem. Sci. 2015, 6, 7206-7212;
b) A. Singh, C. J. Fennell, J. D. Weaver, Chem. Sci. 2016, 7, 6796-6802;
c) S. Senaweera, J. D. Weaver, J. Am. Chem. Soc. 2016, 138, 2520-
2523; d) S. Priya, J. D. Weaver, J. Am. Chem. Soc. 2018, 140, 16020-
16025.
Keywords: polyfluoroarene • boryl radical • hydrogen atom
transfer • photocatalysis • defluoroborylation
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Angewandte Chemie International Edition
RESEARCH ARTICLE
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10.1002/anie.201911819
Angewandte Chemie International Edition
RESEARCH ARTICLE
Entry for the Table of Contents
RESEARCH ARTICLE
Wengang Xu, Heming Jiang, Jing Leng,
Han-Wee Ong, and Jie Wu*
Page No. – Page No.
Visible-Light-Induced Selective
Defluoroborylation of
Polyfluoroarenes, gem-
Difluoroalkenes, and
Trifluoromethylalkenes
A practical and selective defluoroborylation of polyfluoroarenes, gem-difluoroalkenes,
and trifluoromethylalkenes was developed through photoredox and hydrogen atom
transfer-induced B–H activation to synthesize fluorinated organoboranes as the
building blocks for value-added organofluorine compounds.
This article is protected by copyright. All rights reserved.