Direct Olefination of Fluorinated Quinoxalines via Cross- Dehydrogenative Coupling Reactions: A New Near-Infrared Probe for Mitochondria

Article abstract of DOI:10.1002/adsc.201700237

A large library of 5,8-distyrylquinoxaline fluorophores was synthesized in good-to-excellent yields via a palladium-catalyzed oxidative C–H/C–H cross-coupling of electron-deficient fluorinated quinoxalines with electron-rich styrenes. The resulting quinoxaline fluorophores (Qu-Fluors) exhibited tunable color emissions with the quantum yields of up to 83% and large Stokes shifts of up to 6236 cm^?1 in dichloromethane. The bioimaging performance of the Qu-Fluors was shown to have potential as near-infrared fluorescent probes for mitochondria. (Figure presented.).

Full text of DOI:10.1002/adsc.201700237

Title: Direct Olefination of Fluorinated Quinoxalines via Cross-
Dehydrogenative Coupling Reactions: A New NIR Probe for
Mitochondria
Authors: Zeyuan Zhang, yiwen Zheng, Zuobang Sun, Zhen Dai,
Ziqiang Tang, Jiangshang Ma, and Chen Ma
This manuscript has been accepted after peer review and appears as an
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content of this Accepted Article.
To be cited as: Adv. Synth. Catal. 10.1002/adsc.201700237
Link to VoR: http://dx.doi.org/10.1002/adsc.201700237

10.1002/adsc.201700237
Advanced Synthesis & Catalysis
FULL PAPER
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
Direct Olefination of Fluorinated Quinoxalines via Cross-
Dehydrogenative Coupling Reactions: A New Near-Infrared
Probe for Mitochondria
Zeyuan Zhang,a Yiwen Zheng,a,c Zuobang Sun,a Zhen Dai,a Ziqiang Tang,a Jiangshan
Ma,a and Chen Ma a,b*
a
School of Chemistry and Chemical Engineering, Shandong University, Jinan, 250100, P R China.
E-mail: chenma@sdu.edu.cn
State Key Laboratory of Natural and Biomimetic Drugs, Peking University, Beijing, 100191, P R China.
Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and
b
c
Chemistry & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, P.R. China.
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.((Please
delete if not appropriate))
Abstract.
A large library of 5,8-distyrylquinoxaline dichloromethane. The bioimaging performance of the Qu-
fluorophores was synthesized in good-to-excellent yields via Fluors was shown to have potential as near-infrared
a palladium-catalyzed oxidative C–H/C–H cross-coupling of fluorescent probes for mitochondria.
electron-deficient fluorinated quinoxalines with electron-rich
styrenes. The resulting quinoxaline fluorophores (Qu-Fluors)
exhibited tunable color emissions with the quantum
yields up to 83% and large Stokes shifts up to 6236 cm−1 in
Keywords: Cross-dehydrogenative coupling; Quinoxaline;
1,4-Divinylbenzene; near-infrared probe; Mitochondrial
imaging and tracking
approaches have garnered significant attention from
the chemical community. As an important part of
CDC, dehydrogenative Heck reaction, or Fujiwara-
Moritani reaction, has attracted more and more
attention in the last two decades.[16]
Introduction
Electron-poor heteroarenes are key components of
organic electronic and photonic materials, including
dye-sensitized solar cells (DSCs),[1] polymer solar
cells,[2] electron-transport materials,[3] and fluorescent
material and dyes.[4] These electron-poor moieties are
mostly incorporated into materials via Suzuki or
Stille cross-couplings using their organometallic,
halide or pseudohalide derivatives. In general,
electron-poor organometallic coupling partners result
in poor yields.[5] Moreover, in many cases, the
synthesis of organometallic and boron derivatives of
electron-poor compounds can be challenging.
Scheme 1. Direct Oxidative C−H/C−H Cross-Coupling of
6,7-Difluoroquinoxalines with Various Olefins.
Recently, C–H activation has been applied to
electron-poor building blocks such as 2,1,3-
benzothiadiazoles,[6] perylene diimides,[7] naphthalene
diimides,[8]
pyridine
thieno[3,4-c]pyrrole-4,6-diones,[9]
N-oxides,[10]
BODIPY,[12]
sulphur-containing
and
heterocycles,[11]
As a consequence of the electron-withdrawing
abilities and planar structure, quinoxaline (Qu)
derivatives, and in particular, 6-fluoroquinoxaline
(MFQu) and 6,7-difluoroquinoxaline (DFQu)
derivatives have been widely incorporated into small
molecules[17] and polymers[18] for solar cells and field-
effect transistors such as DSC sensitizers and emitters
in organic light-emitting diodes (OLED). 1,4-
polyfluorobenzenes.[13] Some of them are involved in
cross-dehydrogenative coupling (CDC) strategy.
CDC has recently emerged as an ideal method for the
formation of carbon–carbon (C–C)[14] and carbon–
heteroatom (C–X) bonds.[15] Because of the
substantial benefits for organic synthesis, CDC
1
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10.1002/adsc.201700237
Advanced Synthesis & Catalysis
Divinylbenzene derivatives have received significant
attention in recent years owing to their highly
fluorescent quantum efficiency and have been
incorporated into OLED and fluorescent probes.[4,19]
Despite the utility of the 1,4-divinylbenzene motif,
multi-step syntheses via cross-aldol condensation and
Wittig reaction are often required to access 1,4-
divinylbenzene derivatives. In addition, the synthesis
of required aldehyde starting material suffers from
harsh reaction conditions, laborious product isolation
procedures, and unsatisfactory yield.
The reaction conditions were optimized using 6,7-
difluoro-2,3-diphenylquinoxaline 1a and styrene 2a
as the model substrates (Table 1). First, 5,8-
distyrylquinoxaline was obtained in 87% yield by
reacting 1a with 2a in the presence of Pd(OAc)2 (5
mol%), using AgNO3 (5 equiv.) and Ag2CO3 (5
equiv.) as the oxidants, 1,10-phenanthroline as ligand
and DMF as the solvent at 130 C (entry 1). Several
types of Ag reagents including Ag2CO3, AgNO3,
AgOAc, Ag2O, AgF, AgTFA, AgOTs, and AgOTf
were screened; AgF provided the best yield (89%),
while no desired product was obtained using Ag2CO3
and Ag2O (Table 1, Entries 2–9). The equivalent of
AgF was also investigated; 5.0 equiv of AgF resulted
in 89% yield, while 4 equiv AgF significantly
lowered the yield (see the Supporting Information).
Furthermore, after screening several different
solvents, the yield did not increase (Table 1, Entries
10–12). When Pd(TFA)2 was used as the catalyst
instead of Pd(OAc)2, the reaction time reduced from
12 h to 7 h, and the desired product was obtained in a
higher yield compared to that using Pd(OAc)2 (92%
and 89%, respectively) (Table 1, Entries 6 and 13).
Other pyridine-containing ligands such as 2,2'-
bipyridine and 4,4'-di-t-butyl-2,2'-bipyridine were
screened; however, no detectable increase in the yield
of 3a was observed (Table 1, Entries 14 and 15).
Herein, we report a double direct olefination of
quinoxaline
derivatives
to
build
5,8-
distyrylquinoxalines via a highly efficient series sp2
C–H activation CDC process. Furthermore, the
properties of the resulting olefinated DFQu
derivatives were characterized in yellow to near-
infrared light-emitting dyes.
Results and Discussion
Table 1. Optimization of reaction conditions for the one-
pot synthesis of 3aa.
Under the optimized reaction conditions, the
substrate scope of this method was investigated
(Scheme 2). Diverse styrenes 2a–l (see the
Supporting Information) were investigated in this
reaction with 6,7-difluoro-2,3-diphenylquinoxalines
1a–c, affording the corresponding products in good-
to-excellent yields. The yields decreased slightly in
the presence of electron-donating substituents on the
aryl ring of styrene (3a: 92% compared to 3d: 82%).
The yield slightly decreased in the presence of
electron-donating substituents on the 2,3-diphenyl of
quinoxaline (3a: 92% compared to 3e: 89%). In
contrast, yields improved in the presence of electron-
withdrawing substituents on the 2,3-diphenyl of
quinoxaline (3o: 84% compared to 3p: 79%). To
further demonstrate the utility and versatility of this
method, several 5-substituted 6,7-difluoro-2,3-
diphenylquinoxaline 1d–f were employed. As shown
in Scheme 3, the desired products 4a–c were obtained
in good yields. It is worth mentioning that 5-bromo-
6,7-difluoroquinoxaline coupled to styrene via the 8-
H preferentially over the 5-Br (Scheme 3c).
Entry [Pd]
[Ag]
AgNO3+
Ag2CO3
Solvent Yield (3a)b
1
Pd(OAc)2
DMF
87%
c
2
3
4
5
6
7
8
9
10
11
12
13d
14d, e
15d, f
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(TFA)2
Pd(TFA)2
Pd(TFA)2
Ag2CO3
AgNO3
AgOAc
Ag2O
AgF
AgTFA
AgTs
AgOTf
AgF
AgF
AgF
AgF
AgF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
trace
72%
37%
trace
89%
52%
20%
45%
DMSO 36%
DMA
NMP
DMF
DMF
DMF
40%
43%
92%
49%
51%
AgF
aReaction conditions: 1a (0.2 mmol), 2a (0.8 mmol), [Pd]
(5 mol%), [Ag] (5 equiv.), 1,10-Phen (10 mol%), solvent
(2 mL), in a sealed tube at 130 oC under N2 atmosphere for
b
c
12 h. Yield of isolated product. AgNO3 (5 equiv.) and
With
a
divergent
library
of
5,8-
d
e
Ag2CO3 (5 equiv.). under N2 atmosphere for 7 h. 2,2'-
bipyridine was used as ligand. f4,4'-di-t-butyl-2,2'-
bipyridine was used as ligand. DMF = N,N-dimethy-
lformamide, DMA = N,N-dimethylacetamide, NMP = N-
methylpyrrolidone, DMSO = dimethyl sulfoxide.
distyrylquinoxalines in hand, the photophysical
properties including absorptions, emissions, and
quantum yields were measured (for details, see the
Supporting Information). It is worth noting that these
quinoxaline fluorophores, named Qu-Fluors, present
color-tunable emissions (λem: 496−660 nm in CH2Cl2)
with large Stokes shifts (up to 6236 cm−1 in CH2Cl2)
2
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10.1002/adsc.201700237
Advanced Synthesis & Catalysis
Scheme 2. Direct Oxidative C−H/C−H Cross-Coupling of 6,7-Difluoroquinoxalines with Various Olefins and Photophysical
Data of the Resulting Productsa
3
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10.1002/adsc.201700237
Advanced Synthesis & Catalysis
4
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10.1002/adsc.201700237
Advanced Synthesis & Catalysis
aReaction conditions: 1 (0.2 mmol), 2 (0.8 mmol), Pd(TFA)2 (5 mol%), AgF (500 mol%), 1,10-Phen (10 mol%), DMF (2
mL), in a sealed tube at 130 oC under N2 atmosphere for 7 h. bIsolated yield. cAbsorption maximum in CH2Cl2 at 10.0 μM.
dEmission maximum in CH2Cl2 at 10.0 μM. eAbsolute quantum yield in CH2Cl2 at 10.0 μM determined with an integrating
sphere system.
depend on the substituent (R2) on the 2,3-diphenyl of
and high fluorescence quantum yields (up to 0.83 in
quinoxaline (Table 3). Slightly higher quantum yields
were obtained in the presence of electron-donating
substituents on the 2,3-diphenyl of quinoxaline (3o:
0.59 compared to 3p: 0.78). An increase in the
electron-withdrawing ability from n-propoxy (3p and
3r) to F (3o and 3s) enables bathochromic shifts of
emission wavelengths from 622 and 641 to 638 and
660 nm, respectively.
CH2Cl2).
To clarify the fluorescence-structure relationship of
Qu-Fluors, the representative data are listed in Tables
2 and 3. First, as listed in Table 2, the emission
wavelengths and quantum yields of Qu-Fluors
significantly depend on the styrene substituent (R1).
The quantum yields increased significantly (from
0.37 to 0.81) in the presence of electron-donating
substituents on the aryl ring of styrene except
compound 3d. In addition, an increase in the
electron-donating ability from Cl (3h) to 4-
diphenylamino (3k) enables bathochromic shifts of
emission wavelengths from 496 to 605 nm. Second,
the quantum yields of Qu-Fluors also significantly
Near-infrared/far red (NIR/FR) fluorophores (λem
=
650–900 nm) play a crucial role in fluorescent
bioimaging owing to their low light scattering,
minimal photodamage, and deep tissue penetration;
therefore, minimizing background interference and
improving image sensitivity.[19] With two near-
5
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10.1002/adsc.201700237
Advanced Synthesis & Catalysis
Scheme 3. Direct Oxidative C−H/C−H Cross-Coupling of 5-Substituted 6,7-Difluoroquinoxalines with Various Olefins
and Photophysical Data of the Resulting Products.
aAbsorption maximum in CH2Cl2 at 10.0 μM. bEmission maximum in CH2Cl2 at 10.0 μM. cAbsolute quantum yield in
CH2Cl2 at 10.0 μM.
Table 2. Effect of Substituents (R1 and R2) on the
infrared emission fluorescence materials (3q and 3s)
Photophysical Property of Qu-Fluorsa
in hand, 3s was explored for the confocal fluorescent
imaging of SiHa cell. Living SiHa cells were
cultivated with 3s (2 µM) in minimum eagle’s
medium (DMEM, containing 10% of fetal bovine
serum (FBS), 100 IU mL−1 of penicillin, and 100 mg
mL−1 of streptomycin) for 30 min at 37 °C and then
washed twice with phosphate buffered solution. To
our delight, 3s successfully penetrated the cell
Stokes
shift
membranes and labeled SiHa cells with a bright red
luminescence, displaying strong fluorescence in
cytosol (Figure 1a). The emission in cytosol sketched
filament morphologies, indicating that 3s may
concentrate in mitochondria. In addition, 3s showed a
large Stokes shift of 149 nm, which can be used to
avoid imaging interference between excitation and
emission.
λabs
(nm) (nm)
λem
Compd R1
R2
ΦF
(cm−1)
4609
4392
4606
4651
4979
4838
4901
4859
H
CH3
OCH3
H
CH3
H
H
H
409
422
435
504
518
544
499
512
535
496
512
0.58
0.59
0.83
0.37
0.52
0.79
0.37
0.56
3a
3b
3c
3e
3f
3g
3h
3i
n-PrO 405
n-PrO 408
n-PrO 425
n-PrO 399
n-PrO 410
OCH3
Cl
In almost all eukaryotic cells, mitochondria play
vital roles as the energy factories of eukaryotic
cells[21] and are also involved in signaling, controlling
the cell cycle, and regulating metabolism, cellular
t-Butyl
Naphthale
n-2-yl
NPh2
Carbazol-
9-yl
n-PrO 419
n-PrO 476
n-PrO 418
512
605
530
4335
4479
5056
0.62
0.81
0.71
3j
3k
3l
differentiation,
cell
growth
and
death.[22]
Consequently, fluorescent probes that can selectively
illuminate cellular mitochondria are in high demand
for monitoring the morphological changes and study
aPhotophysical properties in CH2Cl2 at 10.0 μM.
6
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10.1002/adsc.201700237
Advanced Synthesis & Catalysis
Table 3. Effect of Substituents (R2 and R3) on the
simulate viscosity environment. As shown in Figure 3,
the emission intensities of 3s obviously increased
with increasing volume fraction of Gly. Thus, 3s
could response to high-viscosity environment,
probably ascribed to the fact that certain sticky
mitochondria matrix restricted intramolecular rotation
of 3s and further enhanced its fluorescence in
mitochondria of SiHa cells, fulfilling our speculation.
Moreover, we think that this property of 3s would
benefit its application in improving signal-to-noise
ratio.[24d]
Photophysical Property of Qu-Fluorsa
Stokes
shift
λabs
(nm) (nm)
λem
Compd R3
R2
H
ΦF
(cm−1)
4427
4479
4152
4207
4167
4425
4320
4417
H
484
616
605
631
622
638
652
641
660
0.58
0.81
0.67
0.78
0.59
0.08
0.16
0.04
3d
3k
3n
3p
3o
3q
3r
3s
H
n-PrO 476
500
n-PrO 493
CH3
CH3
CH3
OCH3
H
F
H
504
506
OCH3 n-PrO 502
OCH3 511
F
aPhotophysical properties in CH2Cl2 at 10.0 μM.
important cellular processes.[23] Recently, many
mitochondria-targeted fluorescent probes have been
developed.[24] To further explore the imaging
potential of 3s, co-staining experiment with SiHa
cells using a mitochondria-specific dye, MitoTracker
Green FM (MTG), was performed. The
morphological observations showed that 3s might be
localized in mitochondria. Notably, the images from
channel 1 (red luminescence from 3s) and channel 2
(green luminescence from MTG) overlapped very
well (Figure 2). The Pearson’s coefficient (Rr = 0.94)
was calculated using Image-Pro Plus software, clearly
demonstrating the specific accumulation of 3s into
the mitochondria of living cells.
Figure 2. (a) fluorescent image of SiHa cells stained with
3s (2.0 μM, 30 min) (λex = 561 nm, λem = 580-700nm); (b)
fluorescent image of SiHa cells stained with MTG (200
nM, 30 min) (λex = 473 nm, λem =500-550nm); (c) merged
image of (a and b); (d):DIC, bar = 20 μm
Figure 1. (a) Confocal fluorescence images of SiHa cells
cultured with 3s (2.0 μM, 30 min) (λex = 561 nm, λem
=580−700 nm); (b) DIC; (c) merged image of (a and b),
bar = 20 μm
Figure 3. FL spectra of 3s (25 μM) in DMF/Gly mixtures
(λex = 500 nm, Gly fraction Vol%)
Mitochondrial matrix is well known to supply a
high-viscosity environment; therefore, we speculated
that 3s can target mitochondria owing to its specific
selectivity to viscosity. Thus, the emission spectra of
3s in various viscosity solvents were recorded, as
shown in Figure 3, and the mix solvent of glycerinum
(Gly) and dimethyl formamide (DMF) was chosen to
Conclusion
In conclusion, we developed the first palladium-
catalyzed direct olefination of DFQus via a cross-
dehydrogenative coupling reaction. A series of
symmetrical and unsymmetrical DFQu-olefin
7
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10.1002/adsc.201700237
Advanced Synthesis & Catalysis
structures were obtained in good to excellent yields
under mild reaction conditions with excellent
functional group compatibility. The directly coupled
fluorophores, named Qu-Fluors, exhibited tunable
color emissions with good quantum yields and large
Stokes shifts. In vitro imaging was explored to
demonstrate the potential of the novel Qu-Fluors as
the NIR FL probes for bioimaging applications. This
versatile methodology offers valuable opportunities
for further studies into the properties of quinoxaline
motif in optoelectronic materials.
129.36, 129.15, 128.79, 128.63, 127.32, 121.02 (3,4JC,F
=
6.0, 3.75 Hz, dd), 117.97; 19F NMR (282 MHz, CD2Cl2): δ
-133.05 (s); HRMS calcd for C36H24F2N2 (M+H)+
523.19803; found: 523.1981.
Typical Procedure for the Synthesis of Compounds 4: A
sealable tube (10 mL) was charged with Pd(TFA)2 (3.4 mg,
0.01 mmol), AgF (63 mg, 0.50 mmol), 1,10-phenanthroline
(3.6 mg, 0.02 mmol), compound 1 (0.20 mmol) and
compound 2 (0.40 mmol). DMF (2 mL) was added and the
tube evacuated and backfilled with N2 three times. The
mixture was gradually heated to 130 °C for 7 h, cooled to
room temperature. CH2Cl2 (60 mL) was added to dilute the
mixture. The combined organics were washed with
saturated brine (25 mL), dried over MgSO4, subjected to
filtration, and concentrated in vacuo. The crude product
was purified by flash chromatography on silica gel, eluting
with CH2Cl2/hexane to deliver the compound 4.
Experimental Section
General information
6,7-difluoro-2,3-diphenylquinoxaline and styrene were
prepared according to literature procedures.1-5 Other
reagents were commercially available and were used
without further purification. All reactions were monitored
by thin-layer chromatography (TLC). 1H NMR spectra
were recorded on a Bruker Avance 300 spectrometer at
300 MHz, 400 MHz, and 500 MHz, using CDCl3, CD2Cl2
and DMSO-d6 as solvent and tetramethylsilane (TMS) as
internal standard. 13C NMR spectra were run in the same
instrument at 75 MHz, 100 MHz, and 125 MHz. HRMS
spectra were determined on a Q-TOF6510 spectrograph
(Agilent). UV-vis absorption spectra and fluorescence
spectra measurements were performed with a Hitachi UV-
4100 spectrometer and a Hitachi F-7000 spectrometer,
respectively. The double-stranded DNA-specific dye
Hoechst 33342 and MTG were purchased from Molecular
Probes. PBS buffer solution: 10 mM NaCl,
Na2HPO4·12H2O, NaH2PO4·2H2O, pH = 7.40. Viability of
the cells was assayed using cell proliferation Kit I with the
absorbance of 492 nm being detected using a PerkinElmer
Victor plate reader. Mitochondrial fluorescence detection
was carried out with flow cytometry (ImageStreamX
MarkII). The data were obtained using INSPIRE software
and analyzed using IDEAS Application v6.0 software.
(E)-4-(6,7-Difluoro-2,3-bis(4-propoxyphenyl)-8-styryl-
quinoxalin-5-yl)-N,N-diphenylaniline 4a: A purification
by flash chromatography in petroleum ether
:
dichloromethane = 5 : 1 gave the title compound as a
1
yellow-green solid (132 mg, 85%). H NMR (300 MHz,
CD2Cl2): δ 8.20 (6H, m), 7.81 (2H, J = 8.4 Hz, d), 7.73
(6H, m), 7.54 (6H, m), 7.36 (3H, m), 6.95 (2H, m), 6.83
(2H, m), 4.01 (2H, t), 3.94 (4H, t), 1.90 (4H, m), 1.09(6H,
m); 13C NMR (100 MHz, CD2Cl2): δ 160.18, 160.09,
151.71, 151.08, 140.66, 137.79, 137.59, 137.06, 136.93,
136.11, 135.99, 133.27, 131.29, 131.26, 131.18, 130.87,
129.72, 128.78, 128.43, 128.23, 126.95, 125.99, 123.86,
123.75, 123.47, 121.40, 120.21, 120.08, 117.61, 114.27,
114.12, 109.96, 69.62, 69.55, 22.56, 22.50, 10.24, 10.18;
19F NMR (282 MHz, CDCl3): δ -132.44 (1F, J = 19.8 Hz,
d), -134.59 (1F, J = 19.8 Hz, d); HRMS calcd for
C52H41F2N3O2 (M+H)+ 778.32396; found: 778.3239.
Acknowledgements
We are grateful to the National Science Foundation of China (No.
21572117) and the State Key Laboratory of Natural and
Biomimetic Drugs of Peking University (No. K20140208) for
financial support of this research.
Typical Procedure for the Synthesis of Compounds 3: A
sealable tube (10 mL) was charged with Pd(TFA)2 (3.4 mg,
0.01 mmol), AgF (126 mg, 1.00 mmol), 1,10-
phenanthroline (3.6 mg, 0.02 mmol), compound 1 (0.20
mmol) and compound 2 (0.80 mmol). DMF (2 mL) was
added and the tube evacuated and backfilled with N2 three
times. The mixture was gradually heated to 130 °C for 7 h,
cooled to room temperature. CH2Cl2 (60 mL) was added to
dilute the mixture. The combined organics were washed
with saturated brine (25 mL), dried over MgSO4, subjected
to filtration, and concentrated in vacuo. The crude product
was purified by flash chromatography on silica gel, eluting
with CH2Cl2/hexane to deliver the compound 3.
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6,7-Difluoro-2,3-diphenyl-5,8-di((E)-styryl)quinoxaline
3a： A purification by flash chromatography in petroleum
ether : dichloromethane = 5 : 1 gave the title compound as
1
a yellow-green solid (96 mg, 92%). H NMR (300 MHz,
CD2Cl2): δ 8.20 (2H, J = 17.1 Hz, d), 8.02 (2H, J =17.1 Hz,
d), 7.67 (8H, m), 7.46 (12H, m); 13C NMR (75 MHz,
CD2Cl2): δ 152.85 (1,2JC,F = 256.5, 18.0 Hz, dd), 152.03,
139.32, 138.19, 137.31 (2,3JC,F = 37.5, 6.0 Hz, dd), 131.37,
[3] J. E. Anthony, A. Facchetti, M. Heeney, S. R. Marder,
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