Direct (Het)arylation of fluorinated benzothiadiazoles and benzotriazole with (Het)aryl iodides

Article abstract of DOI:10.1021/jo402675v

A new and controllable method for the preparation of unsymmetrical and symmetrical fluorinated benzothiadiazole (FBT)-arene structures that can be applied in organic optoelectronic materials has been developed. The reaction proceeds under mild reaction conditions with high efficiency and shows excellent functional group compatibility, even toward bromide. Fluorinated benzotriazoles also take part in the reaction.

Full text of DOI:10.1021/jo402675v

Article
pubs.acs.org/joc
Direct (Het)Arylation of Fluorinated Benzothiadiazoles and
Benzotriazole with (Het)Aryl Iodides
Chun-Yang He,† Cai-Zhi Wu,† Feng-Ling Qing,†,‡ and Xingang Zhang*,‡
†College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, 2999 North Renmin Lu, Shanghai 201620,
China
‡Key Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling
Road, Shanghai 200032, China
S
* Supporting Information
ABSTRACT: A new and controllable method for the preparation of unsymmetrical and symmetrical fluorinated
benzothiadiazole (FBT)−arene structures that can be applied in organic optoelectronic materials has been developed. The
reaction proceeds under mild reaction conditions with high efficiency and shows excellent functional group compatibility, even
toward bromide. Fluorinated benzotriazoles also take part in the reaction.
with aryl bromides was reported.11 The two methods are
complementary to each other and provide facile access to
unsymmetrical FBTs.
INTRODUCTION
■
Donor (D)/acceptor (A) moieties play an important role in
advanced functional materials, particularly in organic solar
cells.1 In this context, many electron-poor aromatic units, such
as benzothiadiazole (BT),2 thiazolothiazole (TzTz),3 thieno-
pyrroledione (TPD),4 diketopyrrolopyrrole (DPP),5 and
isoindigo (IID)6 have been developed to meet the increasing
demand in the development of high-performance organic
electronic and optoelectronic materials. Among them, fluori-
nated benzothiadiazoles (FBTs), including 5-fluoro-BT
(MFBT) and 5,6-difluoro-BT (DFBT), have gained great
attention recently7 and show great advantage over their
nonfluorinated counterparts because of the strong electro-
negativity of the fluorine atom(s), which brings about a great
improvement in device performance, such as photovoltaic
performance.8 Generally, FBTs have been introduced into
organic materials through Stille cross-coupling.9 Although it is
reliable, such a process suffers from the use of toxic stannanes
that require additional steps for preparation and are difficult to
handle. Moreover, the preparation of FBT derivatives via such a
strategy often generates symmetrical disubstituted FBTs,7 in
which sometimes an unstable 4,7-diiodo-DFBT10 has to be
used. To date, it remains challenging to access unsymmetrical
FBTs. To address these issues, herein we demonstrate an
efficient and straightforward method for the preparation of
unsymmetrical and symmetrical arylated FBTs via C−H bond
functionalization of FBTs with aryl iodides. The reaction
proceeds under mild reaction conditions with high efficiency
and shows excellent functional group tolerance, even toward
bromide. During the preparation of our manuscript, a
palladium-catalyzed direct C−H functionalization of FBTs
RESULTS AND DISCUSSION
■
We began this study by choosing 4-bromo-DFBT (1)12 as the
starting material on the consideration that if the selective direct
arylation of 1 with aryl halides via C−H activation were feasible,
the resulting arylated DFBT 3 could serve as a versatile building
block through transformation of the bromide. Accordingly,
compound 1 and 1-iodo-4-methylbenzene (2a) were chosen as
the model substrates (Table 1). Initially, a negative result was
obtained for the reaction of 1 with 2a in the presence of
Pd(OAc)2 (5 mol %), PPh3 (10 mol %), and K2CO3 (0.75
equiv) in DMF at 80 °C (entry 1). Inspired by our recent
work,13 we examined Ag2CO3 instead of K2CO3, as Ag2CO3
was previously supposed to abstract halide anions from the
palladium complex, thus making it more electrophilic.14 To our
delight, a 25% yield of 3a was obtained with intact bromide
(entry 2). To improve the reaction efficiency further, different
phosphane ligands and palladium sources were tested (for
details, see the Supporting Information). It turned out that the
bidentate ligand dppe was the optimal choice, providing 3a in
56% yield (entry 3). Among the tested palladium salts (entries
4−7), Pd(PPh3)4 showed a beneficial effect on the reaction
efficiency, affording a 74% yield of 3a (entry 5). The
counteranion of the palladium salt also had a profound
influence on the reaction efficiency. Trifluoroacetate was
Received: December 3, 2013
Published: January 29, 2014
© 2014 American Chemical Society
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methyl ketone, and a nitrile were compatible with the reaction
system, providing their corresponding products in good to
excellent yields (3e−g). Remarkably, the successful formation
of dibromide-substituted compounds 3h and 3i provides good
opportunities for further transformation or polymerization. It
should be mentioned that even when DFBT 1 was treated with
1-bromo-4-iodobenzene at 140 °C, the aryl bromide still
tolerated the reaction conditions and the byproduct resulting
from the coupling of aryl bromide with 1 was not observed.
However, the yield of 3i dramatically decreased to 45% (as
determined by 19F NMR analysis) because of the formation of
some homocoupling product from the aryl iodide. 2-
Iodothiophene and 3-iodothiophene also reacted smoothly,
and moderate yields were obtained (3k, 3l). This is noteworthy
because the FBT−thiophene structure is a key structrual unit in
the development of high-performance optoelectronic materials,
in particular in bulk heterojunction (BHJ) solar cells.7 The
reaction was not restricted to FBTs, as difluorinated
benzotriazole (DFTAZ) 4,12 an important structural motif in
the development of optoelectronic materials,7c was also a
suitable substrate, providing 3m in good yield.
To probe the applicability of this method further, the
selective direct monoarylation of DFBT (5) with aryl iodides
was also tested (Scheme 2). In general, good yields of
monoarylated FBTs 6a−d were obtained with the use of 3
equiv of 5, albeit with the formation of small amounts of the
corresponding diarylated compounds 7. Importantly, mono-
thienylation of 5 still afforded the key structural motif FBT-
thiophene 6e in synthetically useful yield (6e). In addition,
DFTAZ 917 was also a competent coupling partner, providing
6f in 62% yield. However, MFBT (8)18 showed less reactivity
than its difluorinated counterpart 5, and only a moderate yield
of 6g was obtained, probably because of the low acidity of the
C−H that was to be activated.19 To our delight, the formation
of symmetrical diarylated FBT 7b also proceeded smoothly
when the reaction temperature and the loading of aryl iodide
were increased, thus demonstrating the controllability of this
method.
Table 1. Representative Results for Optimization of the
Direct Arylation of DFBT 1 with 2a
a
b
entry
[Pd]
ligand
base
yield of 3a (%)
1
2
3
4
5
6
7
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd2(dba)3
Pd(PPh3)4
Pd(TFA)2
Pd(OPiv)2
Pd(OPiv)2
PdCl2
PPh3
PPh3
dppe
dppe
dppe
dppe
dppe
dppe
dppe
dppe
dppe
dppe
dppe
dppe
dppe
dppe
none
K2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2O
NR
25
56
30
74
60
85 (82)
63
c
8
9
15
10
Pd(OPiv)2
Pd(OPiv)2
Pd(OPiv)2
Pd(OPiv)2
Pd(OPiv)2
Pd(OPiv)2
none
26
d
11
AgOAc
Ag2CO3
Ag2CO3
Ag2CO3
none
20
e
12
(91)
(74)
33
f
13
g
14
15
16
17
8
Ag2CO3
none
NR
NR
Pd(OPiv)2
a
Reaction conditions (unless otherwise specified): 1 (1.5 equiv), 2a
b
(0.2 mmol), base (0.75 equiv), DMF (1.5 mL), 6 h. NMR yields as
determined by 19F NMR spectroscopy using fluorobenzene as an
c
internal standard (isolated yields are shown in parentheses). 0.05
equiv of dppe was used. 1.5 equiv of AgOAc was used. The reaction
was conducted for 12 h. 0.4 mmol scale, Pd(OPiv)2 (2.5 mol %), dppe
(5 mol %), DMF (1.5 mL), 12 h. Pd(OPiv)2 (1 mol %), dppe (2 mol
d
e
f
g
%) in DMF (1.5 mL), 12 h.
comparable with acetate (entry 6), but the use of PivO−
dramatically improved the yield to 82% (entry 7). We supposed
that PivO− may function as a proton shuttle during the C−H
cleavage step in FBT 1.15,16 The choice of the silver salt was
also found to be crucial for the reaction efficiency, as Ag2O and
AgOAc both showed little effect (entries 10 and 11). The
reaction is not so sensitive to the nature of the solvent, as the
polar solvent DMSO, the nonpolar solvent toluene, and other
solvents (dioxane and dichloroethane) were all suitable reaction
media, leading to 3a in slightly lower yields (see the Supporting
Information). Finally, an optimal yield (91%) of 3a was
obtained by prolonging the reaction time to 12 h (entry 12). It
is noteworthy that even when the Pd(OPiv)2 loading was
reduced to 2.5 mol %, a good yield of 3a was still obtained
(entry 13). The control experiments showed that palladium,
phosphane ligand, and silver salt are essential for the reaction
(entries 15−17), demonstrating that a Pd(0/II) redox catalytic
cycle is involved in the reaction.
With the optimized conditions in hand (Table 1, entry 12), a
variety of (hetero)aryl iodides 2 were investigated (Scheme 1).
An excellent yield was obtained when 1-iodo-3-methylbenzene
was used (3b). However, the steric effect dramatically
influenced the reaction efficiency, and moderate yields were
obtained when sterically hindered substrates were employed,
such as 1-iodo-2-methylbenzene and 1-iodonaphthalene (3c,
3d). Upon further optimization of the reaction conditions by
increasing the reaction temperature to 100 °C, the yield of 3c
improved to 64%. Versatile functional groups such as an ester, a
To demonstrate the utility of this method, the unsymmetrical
diarylated DFBT 11, which can be used in organic
optoelectronic materials, was prepared in an efficient manner
through Suzuki−Miyaura coupling between 3a and arylboronic
acid 10 (Scheme 3a). Furthermore, the coupling of 6c with aryl
iodide 2g also proceeded smoothly, providing unsymmetrical
diarylated DFBT 12 in high yield (Scheme 3b). However, a
one-pot strategy to prepare compound 12 through sequential
C−H bond arylation failed as a result of deactivation of the
palladium catalyst in the second coupling.
CONCLUSION
■
An efficient and controllable method for the preparation of
arylated FBTs has been developed. The notable advantages of
this protocol are its synthetic simplicity, high efficiency, mild
reaction conditions, and excellent functional group compati-
bility. Thus, this protocol provides facile access to symmetrical
and unsymmetrical FBT derivatives that can be applied in
organic optoelectronic materials.
EXPERIMENTAL SECTION
■
General Procedure for the Selective Arylation of FBT 1 with
Aryl Iodides. To a 25 mL Schlenk tube were added Pd(OPiv)2 (5
mol %), dppe (8.0 mg, 0.1 equiv), aryl iodide (0.2 mmol, 1.0 equiv),
Ag2CO3 (41.7 mg, 0.75 equiv), and FBT 1 (75 mg, 1.5 equiv) under
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a
Scheme 1. Direct Arylation of DFBT 1 and DFTAZ 4 with Aryl Iodides
a
b
Reaction conditions (unless otherwise specified): 1 (1.5 equiv), 2 (0.2 mmol), DMF (1.5 mL). All of the reported yields are isolated yields. The
c
reaction was conducted at 100 °C. Pd(PPh3)4 (5 mol %), (oxidi-2,1 phenylene)bis(diphenylphosphine) (0.1 equiv), DMF (1.5 mL).
N2, followed by DMF (1.5 mL) with stirring. The reaction mixture was
stirred at 80 °C (oil bath). After 12 h of stirring, the reaction mixture
was cooled to room temperature, diluted with dichloromethane,
washed with brine, dried over Na2SO4, filtered, and concentrated. The
residue was purified by silica gel chromatography to provide the pure
product.
Hz, 20.1 Hz), 149.88 (d, J = 5.2 Hz), 149.87 (dd, J = 257.9 Hz, 18.4
Hz), 148.8 (d, J = 18.2 Hz), 138.3, 130.9 (d, J = 2.5 Hz), 130.2, 129.4
(m), 128.5, 127.4 (d, J = 2.6 Hz), 119.7 (d, J = 14.1 Hz), 97.4 (dd, J =
21.5 Hz, 2.0 Hz), 21.5. MS (EI-quadrupole): m/z (%) 342 (M+, 100),
340 (M+, 100), 329, 327, 261, 246. HRMS (EI-TOF): calcd for
C13H7N F2SBr, 339.9481; found, 339.9480.
2
4-Bromo-5,6-difluoro-7-(o-tolyl)benzo[c][1,2,5]thiadiazole (3c).
The product (31 mg, 45% yield at 80 °C; 44 mg, 64% yield at 100
°C) was purified by silica gel chromatography (PE/DCM = 50:1) as a
4-Bromo-5,6-difluoro-7-(p-tolyl)benzo[c][1,2,5]thiadiazole (3a).
The product (62 mg, 91% yield) was purified by silica gel
chromatography (PE/DCM = 50:1) as a yellow solid. Mp: 122 °C.
1H NMR (400 MHz, CDCl3): δ 7.65 (d, J = 7.2 Hz, 2H), 7.37 (d, J =
7.2 Hz, 2H), 2.46 (s, 3H). 19F NMR (376 MHz, CDCl3): δ −120.0 (d,
J = 19.7 Hz, 1F), −132.0 (d, J = 19.7 Hz, 1F). 13C NMR (100 MHz,
1
white solid. Mp: 92 °C. H NMR (400 MHz, CDCl3): δ 7.48−7.39
(m, 2H), 7.39−7.30 (m, 2H), 2.17 (s, 3H). 19F NMR (376 MHz,
CDCl3): δ −120.0 (d, J = 21.2 Hz, 1F), −127.6 (d, J = 21.2 Hz, 1F).
13C NMR (100 MHz, CDCl ): δ 152.1 (dd, J = 257.4 Hz, 20.4 Hz),
3
CDCl ): δ 152.3 (dd, J = 256.4 Hz, 20.4 Hz), 149.9 (d, J = 5.3 Hz),
3
150.0 (dd, J = 257.0 Hz, 18.2 Hz), 149.8 (d, J = 8.3 Hz), 149.6 (d, J =
4.9 Hz), 137.1, 130.6, 130.3, 129.6, 129.0, 125.9, 119.6 (d, J = 17.4
Hz), 98.6 (d, J = 21.7 Hz), 20.0. MS (EI-quadrupole): m/z (%) 342
(M+, 100), 340 (M+, 100), 322, 320, 261, 241. HRMS (EI-TOF):
149.8 (dd, J = 257.6 Hz, 18.4 Hz), 149.5 (d, J = 7.8 Hz), 139.6, 130.2
(d, J = 2.8 Hz), 129.3, 126.6 (m), 119.5 (d, J = 13.9 Hz), 97.8 (d, J =
19.2 Hz), 21.4. MS (EI-quadrupole): m/z (%) 342 (M+, 100), 340
(M+, 100), 329, 327, 261, 241. HRMS (EI-TOF): calcd for C13H7N
2F2SBr, 339.9481; found, 339.9485.
4-Bromo-5,6-difluoro-7-(m-tolyl)benzo[c][1,2,5]thiadiazole (3b).
The product (63 mg, 93% yield) was purified by silica gel
chromatography (PE/DCM = 50:1) as a yellow solid. Mp: 114 °C.
1H NMR (400 MHz, CDCl3): δ 7.54 (s, 1H), 7.53 (d, J = 7.6 Hz, 1H),
7.45 (t, J = 7.6 Hz, 1H), 7.33 (d, J = 7.2 Hz, 1H), 2.47 (s, 3H). 19F
NMR (376 MHz, CDCl3): δ −120.0 (d, J = 20.5 Hz, 1F), −131.5 (d, J
= 20.5 Hz, 1F). 13C NMR (125 MHz, CDCl 3): δ 152.3 (dd, J = 256.4
calcd for C13H7N F2SBr, 339.9481; found, 339.9478.
2
4-Bromo-5,6-difluoro-7-(naphthalen-1-yl)benzo[c][1,2,5]-
thiadiazole (3d). The product (40 mg, 53%) was purified by silica gel
chromatography (PE/DCM = 50:1) as a pale-yellow solid. Mp: 105
°C. 1H NMR (400 MHz, CDCl3): δ 8.06 (d, J = 8.4 Hz, 1H), 7.98 (d,
J = 8.0 Hz, 1H), 7.66 (d, J = 7.4 Hz, 1H), 7.60 (dd, J = 6.8 Hz, 0.8 Hz,
1H), 7.54 (m, 1H), 7.42 (m, 2H). 19F NMR (376 MHz, CDCl3): δ
−119.9 (d, J = 20.5 Hz, 1F), −126.0 (d, J = 20.5 Hz, 1F). 13C NMR
(125 MHz, CDCl 3): δ 152.1 (dd, J = 257.4 Hz, 20.1 Hz), 150.6 (dd, J
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a
Scheme 2. Selective Arylation of FBTs and DFTAZ with Aryl Iodides
a
Reaction conditions (unless otherwise specified): 5, 8, or 9 (3 equiv), 2 (0.2 mmol), DMF (1.5 mL), 12 h. All of the reported yields of 6 are
b
isolated yields; the numbers in the parentheses are the NMR yields of 7 determined by 19F NMR spectroscopy. Pd(PPh3)4 (5 mol %), (oxidi-2,1-
phenylene)bis(diphenylphosphine) (0.1 equiv), DMF (1.5 mL). The reaction was performed on a 0.4 mmol scale in 1.5 mL of DMF. 5 (0.2
mmol), 2 (3 equiv), Pd(OPiv)2 (5 mol %), dppe (0.1 equiv), Ag2CO3 (1.5 equiv), DMF (1.5 mL), 100 °C, 12 h.
c
d
Scheme 3. Syntheses of Unsymmetrical Diarylated FBTs 11 and 12
= 258.2 Hz, 18.1 Hz), 150.2 (d, J = 7.9 Hz), 149.7 (d, J = 5.1 Hz),
133.7, 131.3, 130.1, 128.8, 128.7, 127.0 (d, J = 2.2 Hz), 126.7, 126.3,
125.2, 125.0, 118.5 (d, J = 16.2 Hz), 99.1 (d, J = 21.2 Hz). MS (EI-
quadrupole): m/z (%) 378 (M+), 376 (M+), 377 (M+, 100), 375 (M+,
100). HRMS (EI-TOF): calcd for C16H7N2F2SBr, 375.9481; found,
375.9479.
Ethyl 4-(7-Bromo-5,6-difluorobenzo[c][1,2,5]thiadiazol-4-yl)-
benzoate (3e). The product (69 mg, 86% yield) was purified by
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silica chromatography (PE/DCM = 5:1) as a white solid. Mp: 149 °C.
1H NMR (400 MHz, CDCl3): δ 8.23 (d, J = 8.8 Hz, 2H), 7.85 (dd, J =
8.2 Hz, 1.4 Hz, 2H), 4.43 (q, J = 7.1 Hz, 2H), 1.43 (t, J = 7.1 Hz, 3H).
19F NMR (376 MHz, CDCl3): δ −119.8 (d, J = 20.3 Hz, 1F), −130.7
Hz), 55.4. MS (MALDI-TOF): m/z (%) 358 (M+), 356 (M+), 355
(M+). HRMS (MALDI-FTMS): calcd for C13H7N2OSF2Br, 355.9425;
found, 355.9439.
4-Bromo-5,6-difluoro-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole
(3k). The reaction was carried out with Pd(PPh3)4 (0.05 mol %) and
(oxidi-2,1-phenylene)bis(diphenylphosphine) (0.1 equiv) in DMF
(1.5 mL). The product (41 mg, 62% yield) was purified by silica gel
chromatography (PE/DCM = 30:1) as an orange solid. Mp: 149 °C.
1H NMR (400 MHz, CDCl3): δ 8.24 (d, J = 3.2 Hz, 1H), 7.63 (d, J =
(d, J = 20.3 Hz, 1F). 13C NMR (100 MHz, CDCl ): δ 166.0, 153.3
3
(dd, J = 256.8 Hz, 20.1 Hz), 150.2 (dd, J = 259.6 Hz, 18.6 Hz), 149.9
(d, J = 5.0 Hz), 149.0 (d, J = 7.6 Hz), 133.9 (m), 131.2, 130.4 (d, J =
2.9 Hz), 129.7, 118.4 (d, J = 13.7 Hz), 99.2 (d, J = 21.5 Hz), 61.2, 14.3.
MS (MALDI-TOF): m/z (%) 401 (M+), 399 (M+), 397 (M+). HRMS
(MALDI-FTMS): calcd for C15H10N 2O2F2SBr, 398.9609; found,
398.9619.
5.2 Hz, 1H), 7.26 (d, J = 3.6 Hz, 1H). 19F NMR (376 MHz, CDCl3): δ
−120.2 (d, J = 18.4 Hz, 1F), −126.8 (d, J = 18.4 Hz, 1F). 13C NMR
(100 MHz, CDCl3): δ 152.4 (dd, J = 255.5 Hz, 20.0 Hz), 149.8 (d, J =
5.4 Hz), 149.2 (dd, J = 261.2 Hz, 19.2 Hz), 147.8 (d, J = 11.2 Hz),
131.3 (d, J = 8.4 Hz), 130.7 (m), 129.4 (d, J = 6.6 Hz), 127.5, 113.3
(d, J = 9.3 Hz), 97.0 (d, J = 21.9 Hz). MS (EI-quadrupole): m/z (%)
334 (M+, 100), 332 (M+, 97), 288, 253. HRMS (EI-TOF): calcd for
C10H3N2F2S2Br, 331.8889; found, 331.8884.
4-(7-Bromo-5,6-difluorobenzo[c][1,2,5]thiadiazol-4-yl)-
benzonitrile (3f). The product (56 mg, 80% yield) was purified by
silica chromatography (PE/DCM = 5:1) as a white solid. Mp: 147 °C.
1H NMR (400 MHz, CDCl3): δ 7.91 (d, J = 8.2 Hz, 2H), 7.84 (d, J =
8.2 Hz, 2H). 19F NMR (376 MHz, CDCl3): δ −119.7 (d, J = 19.0 Hz,
1F), −130.3 (d, J = 19.0 Hz, 1F). 13C NMR (125 MHz, CDCl ): δ
3
4-Bromo-5,6-difluoro-7-(thiophen-3-yl)benzo[c][1,2,5]thiadiazole
(3l). The reaction was carried out with Pd(PPh3)4 (0.05 mol %) and
(oxidi-2,1-phenylene)bis(diphenylphosphine) (0.1 equiv) in DMF
(1.5 mL). The product (25 mg, 38% yield) was purified by silica gel
151.8 (dd, J = 256.9 Hz, 19.8 Hz), 149.9 (dd, J = 260.5 Hz, 18.8 Hz),
149.88 (d, J = 5.0 Hz), 148.5 (d, J = 7.5 Hz), 134.1, 132.2, 131.1 (d, J
= 3.0 Hz), 118.2, 117.2 (d, J = 13.2 Hz), 113.0, 100.0 (dd, J = 21.2 Hz,
2.1 Hz). MS (EI-quadrupole): m/z (%) 353 (M+, 100), 351 (M+, 98),
1
chromatography (PE/DCM = 30:1) as a yellow solid. Mp: 98 °C. H
273. HRMS (EI-TOF): calcd for C13H4BrF2N S, 350.9277; found,
3
NMR (400 MHz, CDCl3): δ 8.32 (d, J = 2.8 Hz, 1H), 7.88 (ddd, J =
4.8 Hz, 2.0 Hz, 1.2 Hz, 1H), 7.51 (dd, J = 5.0 Hz, 3.0 Hz, 1H). 19F
NMR (376 MHz, CDCl3): δ −120.0 (d, J = 19.0 Hz, 1F), −129.2 (d, J
= 19.0 Hz, 1F). 13C NMR (100 MHz, CDCl3): δ 152.4 (dd, J = 255.7
Hz, 20.4 Hz), 149.9 (d, J = 5.3 Hz), 149.7 (dd, J = 259.2 Hz, 18.7 Hz),
148.6 (d, J = 8.6 Hz), 129.4 (t, J = 3.0 Hz), 128.64 (d, J = 5.6 Hz),
128.58 (d, J = 4.6 Hz), 114.1 (d, J = 12.7 Hz), 97.4 (dd, J = 21.5 Hz,
2.1 Hz). MS (EI-quadrupole): m/z (%) 334 (M+, 100), 332 (M+, 97),
253, 220. HRMS (EI-TOF): calcd for C10H3N2F2S2Br, 331.8889;
found, 331.8887.
350.9276.
1-(4-(7-Bromo-5,6-difluorobenzo[c][1,2,5]thiadiazol-4-yl)phenyl)-
ethanone (3g). The product (68 mg, 92% yield) was purified by silica
gel chromatography (PE/DCM = 5:1) as a white solid. Mp: 159 °C.
1H NMR (400 MHz, CDCl3): δ 8.13 (d, J = 8.0 Hz, 2H), 7.88 (d, J =
8.0 Hz, 2H), 2.68 (s, 3H). 19F NMR (376 MHz, CDCl3): δ −119.8 (d,
J = 19.9 Hz, 1F), −130.6 (d, J = 19.9 Hz, 1F). 13C NMR (100 MHz,
CDCl ): δ 197.4, 152.1 (dd, J = 256.8 Hz, 20.1 Hz), 150.0 (dd, J =
3
259.8 Hz, 18.8 Hz), 149.9 (d, J = 5.2 Hz), 148.9 (d, J = 7.0 Hz), 137.4,
134.2, 130.7, 128.4, 118.2 (d, J = 13.5 Hz), 99.3 (d, J = 21.4 Hz), 26.7.
MS (EI-quadrupole): m/z (%) 370 (M+), 368 (M+), 355 (98), 353
(100). HRMS (EI-TOF): calcd for C14H7F2N2BrSO, 367.9431; found,
367.9433.
1-(4-(7-Bromo-5,6-difluoro-2-octyl-2H-benzo[d][1,2,3]triazol-4-
yl)phenyl)ethanone (3m). The reaction was carried out with DFTAZ
4 instead of FBT 1. The product (66 mg, 71% yield) was purified by
1
silica gel chromatography (PE/DCM = 5:1) as a pale-yellow oil. H
4-Bromo-7-(4-bromo-3-fluorophenyl)-5,6-difluorobenzo[c]-
[1,2,5]thiadiazole (3h). The product (34 mg, 40% yield) was purified
by silica gel chromatography (PE/DCM = 50:1) as a white solid. Mp:
150 °C. 1H NMR (400 MHz, CDCl3): δ 7.72 (d, J = 8.0 Hz, 1H), 7.59
(d, J = 14.0 Hz, 1H), 7.47 (d, J = 8.0 Hz, 1H). 19F NMR (376 MHz,
CDCl3): δ −106.1 (apparent t, J = 8.3 Hz, 1F), −119.7 (d, J = 19.7 Hz,
1F), −130.5 (d, J = 19.7 Hz, 1F). 13C NMR (125 MHz, CDCl3): δ
158.9 (d, J = 246.5 Hz), 152.0 (dd, J = 256.8 Hz, 20.0 Hz), 150.1 (dd,
J = 260.0 Hz, 18.6 Hz), 149.9 (d, J = 5.1 Hz), 148.6 (d, J = 7.5 Hz),
133.6, 130.4 (dm, J = 8.9 Hz), 127.2 (t, J = 3.6 Hz), 118.5 (dd, J = 24.1
Hz, 3.1 Hz), 117.0 (dm, J = 13.2 Hz), 110.5 (d, J = 20.8 Hz), 99.4 (dd,
J = 21.4 Hz, 2.1 Hz). MS (EI-quadrupole): m/z (%) 426 (M+), 425
(M+), 424 (M+, 100), 345, 343. HRMS (EI-TOF): calcd for
C12H3Br2F3N2S, 421.8336; found, 421.8337.
4-Bromo-7-(4-bromophenyl)-5,6-difluorobenzo[c][1,2,5]-
thiadiazole (3i). The product (68 mg, 84% yield at 100 °C) was
purified by silica gel chromatography (PE/DCM = 50:1) as a white
solid. Mp: 160 °C. 1H NMR (400 MHz, CDCl3): δ 7.69 (d, J = 8.4 Hz,
2H), 7.65 (d, J = 8.4 Hz, 2H). 19F NMR (376 MHz, CDCl3): δ −119.8
(d, J = 19.7 Hz, 1F), −131.2 (d, J = 19.7 Hz, 1F). 13C NMR (100
MHz, CDCl3): δ 152.2 (dd, J = 256.5 Hz, 20.1 Hz), 149.94 (dd, J =
258.8 Hz, 18.4 Hz), 149.9 (d, J = 5.1 Hz), 149.0 (d, J = 7.6 Hz), 131.9
(d, J = 2.8 Hz), 131.86, 128.4, 123.9, 118.2 (d, J = 13.8 Hz), 98.8 (d, J
= 21.5 Hz). MS (EI-quadrupole): m/z (%) 408 (M+), 406 (M+, 100),
404 (M+), 327, 325. HRMS (EI-TOF): calcd for C12H4N2Br2F2S,
403.8430; found, 403.8424.
NMR (400 MHz, CDCl3): δ 8.09 (d, J = 8.8 Hz, 2H), 7.96 (d, J = 8.8
Hz, 2H), 4.71 (t, J = 7.2 Hz, 2H), 2.65 (s, 3H), 2.10 (m, 2H), 1.45−
1.20 (m, 10H), 0.85 (t, J = 7.0 Hz, 3H). 19F NMR (376 MHz, CDCl3):
δ −128.2 (d, J = 19.7 Hz, 1F), −137.0 (d, J = 19.7 Hz, 1F). 13C NMR
(100 MHz, CDCl3): δ 197.4, 149.4 (dd, J = 248.9 Hz, 19.2 Hz), 147.6
(dd, J = 253.2 Hz, 17.8 Hz), 139.8 (d, J = 5.1 Hz), 138.0 (d, J = 7.7
Hz), 136.9, 134.8, 130.3 (d, J = 3.5 Hz), 128.4, 116.1 (d, J = 13.7 Hz),
96.1 (d, J = 22.0 Hz), 57.2, 31.6, 30.0, 29.0, 28.8, 26.6, 26.4, 22.5, 14.0.
MS (MALDI-TOF): m/z (%) 464 (M+), 462 (M+). HRMS (MALDI-
FTMS): calcd for C22H24N3F2OBr, 462.0987; found, 462.0996.
General Procedure for the Preparation of Compounds 6a−d
and 6f. To a 25 mL Schlenk tube were added Pd(OPiv)2 (5 mol %),
dppe (8.0 mg, 0.1 equiv), aryl iodide (0.2 mmol, 1.0 equiv), Ag2CO3
(41.7 mg, 0.75 equiv), and FBT 5 or DFTAZ 9 (3.0 equiv) under N2,
followed by DMF (1.5 mL) with stirring. The reaction mixture was
stirred at 80 °C (oil bath). After 12 h of stirring, the reaction mixture
was cooled to room temperature, diluted with dichloromethane,
washed with brine, dried over Na2SO4, filtered, and concentrated. The
residue was purified by silica gel chromatography to provide the pure
product.
5,6-Difluoro-4-(4-methoxyphenyl)benzo[c][1,2,5]thiadiazole
(6a). The product (44 mg, 79%) was purified by silica gel
chromatography (PE/DCM = 30:1) as a yellow solid. Mp: 127 °C.
1H NMR (400 MHz, CDCl3): δ 7.75 (d, J = 8.0 Hz, 2H), 7.68
(apparent t, J = 8.4 Hz, 1H), 7.08 (d, J = 8.0 Hz, 2H), 3.89 (s, 3H). 19F
NMR (376 MHz, CDCl3): δ −127.1 (dd, J = 19.0 Hz, 9.6 Hz, 1F),
−134.8 (dd, J = 18.4 Hz, 7.5 Hz, 1F). 13C NMR (125 MHz, CDCl3): δ
160.2, 154.4 (dd, J = 256.8 Hz, 19.3 Hz), 150.8 (d, J = 7.5 Hz), 150.6
(d, J = 12.2 Hz), 149.4 (dd, J = 255.1 Hz, 18.4 Hz), 131.8 (d, J = 3.0
Hz), 122.3, 120.0 (d, J = 11.8 Hz), 114.0, 104.1 (d, J = 20.0 Hz), 55.3.
MS (EI-quadrupole): m/z (%) 278 (M+), 263, 235. HRMS (EI-TOF):
calcd for C13H8N2OF2S, 278.0325; found, 278.0327.
4-Bromo-5,6-difluoro-7-(4-methoxyphenyl)benzo[c][1,2,5]-
thiadiazole (3j). The product (37 mg, 52% yield) was purified by silica
gel chromatography (PE/DCM = 30:1) as a yellow solid. Mp: 127 °C.
1H NMR (400 MHz, CDCl3): δ 7.74 (d, J = 8.6 Hz, 2H), 7.08 (d, J =
8.6 Hz, 2H), 3.90 (s, 3H). 19F NMR (376 MHz, CDCl3): δ −120.1 (d,
J = 20.5 Hz, 1F), −132.5 (d, J = 20.5 Hz, 1F). 13C NMR (100 MHz,
CDCl3): δ 160.4, 152.4 (dd, J = 256.2 Hz, 20.3 Hz), 149.9 (d, J = 5.2
Hz), 149.6 (d, J = 7.9 Hz), 149.5 (dd, J = 257.0 Hz, 18.2 Hz), 131.8
(d, J = 2.7 Hz), 121.8, 119.2 (d, J = 14.1 Hz), 114.1, 97.4 (d, J = 19.2
1-(4-(5,6-Difluorobenzo[c][1,2,5]thiadiazol-4-yl)phenyl)ethanone
(6b). The product (42 mg, 72% yield) was purified by silica gel
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Article
1
chromatography (PE/DCM = 5:1) as a white solid. Mp: 144 °C. H
NMR (400 MHz, CDCl3): δ 8.15 (d, J = 8.6 Hz, 2H), 7.90 (d, J = 8.6
Hz, 2H), 7.78 (dd, J = 9.4 Hz, 7.4 Hz, 1H), 2.68 (s, 3H). 19F NMR
(376 MHz, CDCl3): δ −126.9 (dd, J = 17.9 Hz, 9.6 Hz, 1F), −132.8
(dd, J = 17.7 Hz, 8.3 Hz, 1F). 13C NMR (100 MHz, CDCl3): δ 197.5,
154.1 (dd, J = 257.7 Hz, 19.0 Hz), 150.5 (d, J = 12.1 Hz), 150.2 (d, J =
7.3 Hz), 150.1 (dd, J = 258.2 Hz, 18.7 Hz), 137.2, 134.7, 130.7 (d, J =
2.8 Hz), 128.4, 119.0 (d, J = 11.6 Hz), 105.5 (d, J = 19.9 Hz), 26.7. MS
(EI-quadrupole): m/z (%) 290 (M+), 275 (100), 247. HRMS (EI-
TOF): calcd for C14H8N2F2SO, 290.0325; found, 290.0323.
Ethyl 4-(5,6-Difluorobenzo[c][1,2,5]thiadiazol-4-yl)benzoate (6c).
The product (46 mg, 72%) was purified by silica gel chromatography
(PE/DCM = 5:1) as a white solid. Mp: 120 °C. 1H NMR (400 MHz,
CDCl3): δ 8.23 (d, J = 8.8 Hz, 2H), 7.86 (d, J = 8.8 Hz, 2H), 7.77 (dd,
J = 9.6 Hz, 7.6 Hz, 1H), 4.43 (q, J = 7.2 Hz, 2H), 1.43 (t, J = 7.2 Hz,
3H). 19F NMR (376 MHz, CDCl3): δ −126.9 (dd, J = 18.4 Hz, 9.0 Hz,
1F), −132.9 (dd, J = 17.7 Hz, 6.8 Hz, 1F). 13C NMR (100 MHz,
CDCl3): δ 166.0, 154.1 (dd, J = 257.6 Hz, 19.0 Hz), 150.5 (d, J = 12.1
Hz), 150.3 (d, J = 7.5 Hz), 150.1 (dd, J = 258.1 Hz, 18.6 Hz), 134.4
(m), 131.0, 130.4 (d, J = 2.8 Hz), 129.6, 119.2 (d, J = 14.7 Hz), 105.4
(d, J = 18.5 Hz), 61.2, 14.3. MS (EI-quadrupole): m/z (%) 320 (M+),
292, 275 (100). HRMS (EI-TOF): calcd for C15H10N2O2F2S,
320.0431; found, 320.0429.
4.1 Hz, 1F). 13C NMR (100 MHz, CDCl3): δ 197.6, 159.4 (d, J =
253.1 Hz), 154.0 (d, J = 9.5 Hz), 152.2, 136.7, 135.8, 130.7 (d, J = 2.6
Hz), 128.2, 122.0 (d, J = 11.1 Hz), 121.7 (d, J = 30.8 Hz), 117.6 (d, J =
16.5 Hz), 26.7. MS (EI-quadrupole): m/z (%) 272 (M+), 257 (100),
229. HRMS (EI-TOF): calcd for C14H9N2FSO, 272.0420; found,
272.0425.
1,1′-((5,6-Difluorobenzo[c][1,2,5]thiadiazole-4,7-diyl)bis(4,1-
phenylene))diethanone (7b). The reaction was carried out with 5 (0.2
mmol, 1 equiv), Ag2CO3 (1.5 equiv), 1-(4-iodophenyl)ethanone (3
equiv), Pd(OPiv)2 (5 mol %), and dppe (0.1 equiv) in DMF (1.5 mL)
at 100 °C. The product (73 mg, 89% yield) was purified by silica gel
1
chromatography (PE/EA = 5:1) as a white solid. Mp: 242 °C. H
NMR (400 MHz, CDCl3): δ 8.17 (d, J = 8.4 Hz, 4H), 7.95 (d, J = 8.4
Hz, 4H), 2.69 (s, 6H). 19F NMR (376 MHz, CDCl3): δ −131.9 (s,
2F). 13C NMR (125 MHz, CDCl3): δ 197.4, 150.5 (dd, J = 259.1 Hz,
20.2 Hz), 150.0 (t, J = 3.6 Hz), 137.3, 134.6, 130.8, 128.4, 118.4 (dd, J
= 10.4 Hz, 4.5 Hz), 26.7. MS (EI-quadrupole): m/z (%) 408 (M+),
393 (100), 322, 189. HRMS (EI-TOF): calcd for C22H14N2F2SO2,
408.0744; found, 408.0741.
4-(4-(Diphenylamino)phenyl)-5,6-difluoro-7-(p-tolyl)benzo[c]-
[1,2,5]thiadiazole (11). To a 25 mL Schlenk tube were added 3a (0.4
mmol, 1.0 equiv), (4-(diphenylamino)phenyl)boronic acid (231 mg, 2
equiv), Pd(PPh3)4 (2 mol %), and K2CO3 (220 mg, 4.0 equiv) under
N2, followed by DMF (5 mL) and H2O (1 mL) with stirring. The
reaction mixture was stirred at 110 °C (oil bath). After 10 h of stirring,
the reaction mixture was cooled to room temperature, diluted with
dichloromethane, filtered, washed with brine, dried over Na2SO4, and
concentrated. The product (199 mg, 98% yield) was purified by silica
gel chromatography (PE/DCM = 5:1) as a green yellow solid. Mp:
167 °C. 1H NMR (400 MHz, CDCl3): δ 7.70 (t, J = 6.0 Hz, 4H), 7.36
(d, J = 7.6 Hz, 2H), 7.28 (t, J = 7.6 Hz, 4H), 7.19 (d, J = 8.0 Hz, 6H),
7.07 (t, J = 7.2 Hz, 2H), 2.44 (s, 3H). 19F NMR (376 MHz, CDCl3): δ
−133.5 (d, J = 17.7 Hz, 1F), −133.8 (d, J = 17.7 Hz, 1F). 13C NMR
(125 MHz, CDCl3): δ 150.6 (d, J = 8.5 Hz), 150.43 (d, J = 8.2 Hz),
150.4 (dd, J = 257.8 Hz, 21.8 Hz), 150.1 (dd, J = 252.2 Hz, 16.4 Hz),
148.4, 147.2, 139.0, 131.3 (d, J = 3.1 Hz), 130.3 (d, J = 2.5 Hz), 129.4,
129.2, 127.4, 125.2, 123.6, 123.1, 121.7, 118.1 (dd, J = 19.4 Hz, 13.4
Hz), 21.4. MS (EI-quadrupole): m/z (%) 505 (M+), 245, 91 (100).
HRMS (EI-TOF): calcd for C31H21N3F2S, 505.1424; found, 505.1420.
Ethyl 4-(7-(4-Acetylphenyl)-5,6-difluorobenzo[c][1,2,5]thiadiazol-
4-yl)benzoate (12). To a 25 mL Schlenk tube were added 6c (0.26
mmol, 1.3 equiv), 1-(4-iodophenyl)ethanone (49.2 mg, 1.0 equiv),
Pd(OPiv)2 (5 mol %), dppe (10 mol %), and Ag2CO3 (42 mg, 0.75
equiv) under N2, followed by DMF (1.5 mL) with stirring. The
reaction mixture was stirred at 80 °C (oil bath). After 12 h of stirring,
the reaction mixture was cooled to room temperature, diluted with
dichloromethane, filtered, washed with brine, dried over Na2SO4, and
concentrated. The product (77 mg, 88% yield) was purified by silica
gel chromatography (PE/EA = 20:1) as a yellow solid. Mp: 182 °C. 1H
NMR (400 MHz, CDCl3): δ 8.24 (t, J = 8.4 Hz, 2H), 8.16 (d, J = 8.4
Hz, 2H), 7.94 (d, J = 7.6 Hz, 2H), 7.91 (d, J = 7.6 Hz, 2H), 4.43 (q, J
= 7.2 Hz, 2H), 2.69 (s, 3H), 1.43 (t, J = 7.2 Hz, 3H). 19F NMR (376
MHz, CDCl3): δ −131.96 (d, J = 17.7 Hz, 1F), −132.04 (d, J = 17.7
Hz, 1F). 13C NMR (100 MHz, CDCl3): δ 197.4, 166.0, 150.5 (dd, J =
259.3 Hz, 20.2 Hz), 150.1 (dd, J = 259.0 Hz, 20.4 Hz), 150.06 (d, J =
4.8 Hz), 150.0 (d, J = 4.8 Hz), 137.2, 134.7, 134.3, 131.0, 130.8 (d, J =
2.0 Hz), 130.5 (d, J = 1.9 Hz), 129.6, 128.4, 118.6 (d, J = 12.8 Hz),
118.3 (dd, J = 11.9 Hz, 3.1 Hz), 61.2, 26.7, 14.3. MS (EI-quadrupole):
m/z (%) 438 (M+), 423 (100), 322, 189. HRMS (EI-TOF): calcd for
C23H16N2F2SO3, 438.0850; found, 438.0848.
4-(5,6-Difluorobenzo[c][1,2,5]thiadiazol-4-yl)benzonitrile (6d).
The product (44 mg, 80% yield) was purified by silica gel
1
chromatography (PE/DCM = 5:1) as a white solid. Mp: 163 °C. H
NMR (400 MHz, CDCl3): δ 7.93 (d, J = 7.2 Hz, 2H), 7.84 (d, J = 8.4
Hz, 2H), 7.81 (dd, J = 8.8 Hz, 7.2 Hz, 1H). 19F NMR (376 MHz,
CDCl3): δ −126.7 (dd, J = 19.6 Hz, 8.6 Hz, 1F), −132.5 (dd, J = 18.4
Hz, 7.5 Hz, 1F). 13C NMR (125 MHz, CDCl3): δ 153.9 (dd, J = 257.9
Hz, 18.9 Hz), 150.5 (d, J = 11.9 Hz), 150.2 (dd, J = 259.0 Hz, 18.8
Hz), 149.8 (d, J = 7.1 Hz), 134.7 (m), 132.2, 131.2 (d, J = 3.1 Hz),
118.4, 118.1 (dd, J = 12.9 Hz, 1.8 Hz), 112.9, 106.1 (dd, J = 19.8 Hz,
1.6 Hz). MS (EI-quadrupole): m/z (%) 273 (M+, 100), 254, 227.
HRMS (EI-TOF): calcd for C13H5N3SF2, 273.0172; found, 273.0170.
5,6-Difluoro-4-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (6e).
The reaction was carried out with Pd(PPh3)4 (5 mol %) and (oxidi-
2,1-phenylene)bis(diphenylphosphine) (0.1 equiv) in DMF (1.5 mL).
The product (25 mg, 49% yield) was purified by silica gel
chromatography (PE/DCM = 30:1) as a yellow solid. 1H NMR
(400 MHz, CDCl3): δ 8.25 (d, J = 4.0 Hz, 1H), 7.61 (apparent t, J =
8.2 Hz, 1H), 7.60 (d, J = 4.8 Hz, 1H), 7.24 (t, J = 5.2 Hz, 1H). 19F
NMR (376 MHz, CDCl3): δ −127.2 (dd, J = 17.1 Hz, 8.8 Hz, 1F),
−128.7 (dd, J = 16.5 Hz, 6.8 Hz, 1F). 13C NMR (100 MHz, CDCl3): δ
154.3 (dd, J = 256.1 Hz, 19.0 Hz), 150.5 (d, J = 12.5 Hz), 149.1 (d, J =
7.9 Hz), 149.0 (dd, J = 259.5 Hz, 19.1 Hz), 131.2 (m), 131.1 (d, J =
8.3 Hz), 129.0 (d, J = 6.5 Hz), 127.3, 114.0 (d, J = 11.7 Hz), 103.6 (d,
J = 20.2 Hz). MS (EI-quadrupole): m/z (%) 254 (M+, 100), 210.
HRMS (EI-TOF): calcd for C10H4N2F2S2, 253.9784; found, 253.9782.
1-(4-(5,6-Difluoro-2-octyl-2H-benzo[d][1,2,3]triazol-4-yl)phenyl)-
ethanone (6f). The product (48 mg, 62% yield) was purified by silica
1
gel chromatography (PE/DCM = 5:1) as a yellow oil. H NMR (400
MHz, CDCl3): δ 8.10 (d, J = 8.4 Hz, 2H), 7.98 (d, J = 7.2 Hz, 2H),
7.59 (dd, J = 9.2 Hz, 6.8 Hz, 1H), 4.68 (t, J = 7.2 Hz, 2H), 2.66 (s,
3H), 2.08 (m, 2H), 1.40−1.20 (m, 10H), 0.85 (t, J = 7.0 Hz, 3H). 19F
NMR (376 MHz, CDCl3): δ −133.1 (dd, J = 17.9 Hz, 9.6 Hz, 1F),
−139.5 (dd, J = 17.7 Hz, 6.8 Hz, 1F). 13C NMR (125 MHz, CDCl3): δ
197.5, 151.5 (dd, J = 249.0 Hz, 18.2 Hz), 147.6 (dd, J = 251.1 Hz, 17.7
Hz), 139.6 (d, J = 12.2 Hz), 139.2 (d, J = 7.4 Hz), 136.8, 135.4, 130.4
(d, J = 3.4 Hz), 128.3, 116.8 (d, J = 13.3 Hz), 103.1 (d, J = 21.0 Hz),
56.9, 31.6, 29.9, 29.0, 28.9, 26.6, 26.4, 22.5, 14.0. MS (MALDI-TOF):
m/z (%) 387 (M+), 386 (M+). HRMS (MALDI-FTMS): calcd for
C22H26N3OF2, 386.2038; found, 386.2052.
ASSOCIATED CONTENT
1-(4-(5-Fluorobenzo[c][1,2,5]thiadiazol-4-yl)phenyl)ethanone
(6g). The reaction was performed on a 0.4 mmol scale in 1.5 mL of
DMF. The product (58 mg, 53% yield) was purified by silica gel
■
S
* Supporting Information
Representative results for optimization of direct arylation of
1
chromatography (PE/DCM = 5:1) as a white solid. Mp: 156 °C. H
1
DFBT 1 with 2a and copies of H, 13C, and 19F NMR spectra
NMR (400 MHz, CDCl3): δ 8.12 (d, J = 8.0 Hz, 2H), 8.02 (dd, J = 9.4
Hz, 4.6 Hz, 1H), 7.89 (d, J = 6.8 Hz, 2H), 7.57 (t, J = 9.6 Hz, 1H),
2.67 (s, 3H). 19F NMR (376 MHz, CDCl3): δ −113.7 (dd, J = 9.4 Hz,
for new compounds. This material is available free of charge via
the Internet at http://pubs.acs.org.
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Article
Louwen, J. N.; Noltes, J. G.; Spec, A. L. J. Am. Chem. Soc. 1982, 104,
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(15) Lapointe, D.; Fagnou, K. Chem. Lett. 2010, 39, 1118.
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(17) Min, J.; Zhang, Z.-G.; Zhang, S.; Li, Y. Chem. Mater. 2012, 24,
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(18) For the use of MFBTs in the development of small-molecule-
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AUTHOR INFORMATION
Corresponding Author
*E-mail: xgzhang@mail.sioc.ac.cn.
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The National Natural Science Foundation of China (21172242
and 21332010) and SIOC are gratefully acknowledged for
funding this work.
(19) Lafrance, M.; Rowley, C. N.; Woo, T. K.; Fagnou, K. J. Am.
Chem. Soc. 2006, 128, 8754.
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