Novel hole transport materials based on triarylamine/naphtho[2,1-b]benzofunan for efficient green electroluminescent device

Article abstract of DOI:10.1016/j.tet.2017.06.031

Two hole transport materials, N-([1,1'-biphenyl]-4-yl)-9,9-dimethyl-N-(4-(naphtho[2,1-b]benzofuran-6-yl)phenyl)-9H-fluoren-2-amine (DFA) and N-(9,9-dimethyl-9H-fluoren-2-yl)-9,9-dimethyl-7-(naphtho[2,1-b]benzofuran-6-yl)-N-phenyl-9H-fluoren-2-amine (TFA) were designed, synthesized and fully characterized. The photophysical and thermal properties of these two compounds were investigated by UV–vis absorption spectra, photoluminescence spectra, thermogravimetric analysis (TGA) and differential scanning calorimetry analysis (DSC), which indicated that DFA and TFA would be efficient hole transport materials due to their proper HOMO energy levels and excellent thermal stability. Then, green OLEDs with DFA and TFA as hole transport layer, respectively, were fabricated, NPB-based OLEDs was also prepared for comparison. It turned out that DFA- and TFA-based devices exhibited higher efficiencies than that of NPB-based device, and TFA-based device showed the best performances with current efficiency, power efficiency and external quantum efficiency of 41.68 cd/A, 32.04 lm/W and 12.04%, respectively.

Full text of DOI:10.1016/j.tet.2017.06.031

Tetrahedron 73 (2017) 4610e4615
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Novel hole transport materials based on triarylamine/naphtho[2,1-b]
benzofunan for efficient green electroluminescent device
,
**
Panpan Wu a, Guojian Tian a, Mingming Hu a, Hong Lian b, Qingchen Dong b
,
,
, d,
Wenting Liang c ***, Jinhai Huang a *, Jianhua Su a
a Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science & Technology, Shanghai, 200237, PR China
b Ministry of Education Key Laboratory of Interface Science and Engineering in Advanced Materials, Research Center of Advanced Materials Science and
Technology, Taiyuan University of Technology, Taiyuan, 030024, PR China
c Institute of Environmental Science, Shanxi University, Taiyuan, 030006, PR China
d Shanghai Taoe Chemical Technology Co., Ltd, Shanghai, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two hole transport materials, N-([1,1'-biphenyl]-4-yl)-9,9-dimethyl-N-(4-(naphtho[2,1-b]benzofuran-6-
yl)phenyl)-9H-fluoren-2-amine (DFA) and N-(9,9-dimethyl-9H-fluoren-2-yl)-9,9-dimethyl-7-(naphtho
[2,1-b]benzofuran-6-yl)-N-phenyl-9H-fluoren-2-amine (TFA) were designed, synthesized and fully
characterized. The photophysical and thermal properties of these two compounds were investigated by
UVevis absorption spectra, photoluminescence spectra, thermogravimetric analysis (TGA) and differ-
ential scanning calorimetry analysis (DSC), which indicated that DFA and TFA would be efficient hole
transport materials due to their proper HOMO energy levels and excellent thermal stability. Then, green
OLEDs with DFA and TFA as hole transport layer, respectively, were fabricated, NPB-based OLEDs was also
prepared for comparison. It turned out that DFA- and TFA-based devices exhibited higher efficiencies
than that of NPB-based device, and TFA-based device showed the best performances with current effi-
ciency, power efficiency and external quantum efficiency of 41.68 cd/A, 32.04 lm/W and 12.04%,
respectively.
Received 18 April 2017
Received in revised form
7 June 2017
Accepted 16 June 2017
Available online 17 June 2017
Keywords:
naphtho[2,1-b]benzofunan
Hole transport
Stable
Efficient
© 2017 Elsevier Ltd. All rights reserved.
1. Introduction
cathode. The improved OLEDs can achieve higher carrier injection
efficiencies than single-layer device.6,7 Novel OLEDs have become
Organic light- emitting diodes(OLEDs) have caused extensive
and strong attention since the first efficient OLED presented by the
research group of Tang,1 which is mainly attributed to their prop-
erties of small volume, fast response, high luminous efficiency and
large view angle, etc.2e5 The initial OLED was called single-layer
device due to the simple constitution of anode, emitting layer
and cathode. With the rapid development of scientific research, the
construction of OLED has been improved. To date, organic light-
emitting devices are generally fabricated of anode, hole transport
layer(HTL), emitting layer, electron transport layer(ETL) and
vital segment of flat panel displays and lighting equipment.8e12 In
the past decades, great development has been achieved in OLED
materials and devices, however there are some crucial problems to
be solved.13e16
Hole transport materials are one of the key factor for high effi-
cient organic light-emitting diodes, which play the roles of hole
transporter and electron blocker between hole injection layer and
emitting layer. The proper highest occupied molecular orbi-
tal(HOMO) energy level, good thermal stability and excellent film-
forming property are necessary for a satisfied hole transport
material.17e21 Triarylamine type compounds are ideal hole trans-
port materials for OLEDs, which possess high thermal stability,
appropriate HOMO energy level and good solubility.22e25 N,N’-bis-
* Corresponding author. Key Laboratory for Advanced Materials and Institute of
Fine Chemicals, East China University of Science & Technology, Shanghai, 200237,
PR China.
** Corresponding author.
*** Corresponding author.
(3-methylphenyl)-N,N’-bis-phenyl-benzidine(TPD)
and
N,N'-
di(naphthalen-1-yl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine
(NPB) are among the most familiar hole transport materials due to
their excellent hole-transport property, although their poor ther-
mal stability is an obvious defect of them.26e28 For this reason, new
E-mail addresses: dongqingchen@tyt.edu.cn (Q. Dong), liangwt@sxu.edu.cn
(W. Liang), dele12@163.com (J. Huang).
http://dx.doi.org/10.1016/j.tet.2017.06.031
0040-4020/© 2017 Elsevier Ltd. All rights reserved.

P. Wu et al. / Tetrahedron 73 (2017) 4610e4615
4611
hole transport materials need to be explored.
In this work, two triarylamine-based hole transport materials,
N-([1,1'-biphenyl]-4-yl)-9,9-dimethyl-N-(4-(naphtho[2,1-b]
benzofuran-6-yl)phenyl)-9H-fluoren-2-amine(DFA) and N-(9,9
dimethyl-9H-fluoren-2-yl)-9,9-dimethyl-7-(naphtho[2,1-b]
benzofuran-6-yl)-N-phenyl-9H-fluoren-2-amine(TFA)
were
designed and synthesized. According to literature,29 benzofuran
moiety is an ideal electron acceptor with excellent stability, while
dibenzo[b,d]furan moiety can decrease the oxidation potential and
increase the number of delocalized electrons, thus enhancing the
HOMO energy level and facilitating the transport of hole excitons.
Thus, we guessed that the addition of benzene ring on dibenzo-
furan moiety can increase the molecular weight, which can
improve the thermal stabilities and amorphous state of com-
pounds, thereby realizing excellent device performance of the
corresponding OLEDs. Based on the above considerations, the
naphtho[2,1-b]benzofuran was introduced to the structure of these
three compounds, which can boost the molecular planarity and
thermal stability. To verify the hole transport capacity of these two
triarylamine compounds, OLED devices using DFA and TFA as hole
transport materials were fabricated, and evaluated by comparing
with NPB based device in the same structure.
Fig. 1. Normalized UVevis absorption and fluorescence emission spectra of the com-
pounds in tetrahydrofuran solution at room temperature.
transitions of the conjugated aromatic segments, the weaker ab-
sorption peaks for DFA and TFA are respectively located at around
359 nm and 382 nm, which should be derived from the n-p*
transitions for the extended conjugation of triarylamine and
naphtho[2,1-b]benzofuran. The optical energy bandgaps (Eg) of
these two compounds are calculated to be 3.05 eV and 3.01 eV,
respectively, through calculation from the onset of the absorption
spectra. The maximum PL emission peak was located at 467 nm and
469 nm for DFA and TFA, respectively. The mild red-shifted pho-
toluminescence spectrum of TFA compared to that of DFA could be
ascribed to the larger conjugation of TFA.
2. Result and discussion
2.1. Synthesis and characterization
The synthetic routes of the intermediates and target compounds
were shown in Scheme 1. Firstly, the naphtho[2,1-b]benzofuran
was treated with n-BuLi at ꢀ78 ꢁC, followed by reaction with boric
acid triisopropyl ester to give rise to the compound 3. The in-
termediates 1 and 2 were synthesized by BuchwaldeHartwig and
Ullmann reaction according to procedure as reported in literature.
The target products were prepared by Suzuki coupling reaction,
then purified by flash column chromatography and recrystalliza-
tion method with yields of 68% and 92.53%, respectively. The
molecule structures of these compounds were characterized by 1H
NMR, 13C NMR, and high-resolution mass spectrometry(HRMS).
2.3. Thermal properties
The thermal properties of DFA and TFA were investigated by
thermogravimetric analysis (TGA) and differential scanning calo-
rimetry analysis (DSC) under nitrogen atmosphere with a heating
rate of 10 ꢁC/min. As shown in Fig. 2a, the decomposition temper-
atures (Td), which correspond to 5% weight loss, were measured to
be 426 and 408 ꢁC for DFA and TFA, respectively. Meanwhile, their
corresponding glass transition temperatures (Tg) can be found from
DSC curves (Fig. 2b), which were determined to be 122 and 129 ꢁC
for DFA and TFA, respectively. In addition, the whole DSC analysis of
DFA and TFA are showed in Fig. S1 and Fig. S2, respectively, the first
heating eliminated thermal history of these two materials, and the
second heating revealed the original property of these two mate-
rials. Powder XRD did not reveal any sharp reflections (Fig. S3 and
Fig. S4). Hence, XRD and the excellent thermal behaviors indicate
that these two materials are amorphous and thermally stable. The
decomposition (Td) and glass transition (Tg) temperatures are
summarized in Table 1.
2.2. Photophysical properties
The absorption and emission spectra of DFA and TFA were
measured in tetrahydrofuran solution. As shown in Fig. 1 and
Table 1, the stronger UVeVis absorption peaks of DFA and TFA are
similarly located at around 278 nm, which is attributed to the p-p*
2.4. Electrochemical properties
The electrochemical behaviors of these two compounds were
investigated by cyclic voltammograms (CV) using a standard three-
electrode electrochemical cell in an electrolyte solution (0.1M
TBAPF6/DCM), with ferrocene as external reference. The CV curves
of DFA and TFA were shown in Fig. 3, from which the highest
occupied molecular orbital (HOMO) energy level of DFA and TFA
were calculated to be ꢀ5.22eV and ꢀ5.19eV, respectively. The
lowest unoccupied molecular orbital (LUMO) were then deter-
mined to be ꢀ2.17eV and ꢀ2.18eV, respectively, through the
equation of ELUMO ¼ EHOMO þ Eg. The high HOMO energy levels
imply that these two compounds would be ideal hole transport
materials.
Scheme 1. Synthetic routes of the compounds.

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P. Wu et al. / Tetrahedron 73 (2017) 4610e4615
Table 1
The physical properties of DFA and TFA.
Compounds
labs(nm)a
lem(nm)a
Eg(eV)b
HOMO(eV)c
LUMO(eV)d
Tg(ꢁC)e
Td(ꢁC)f
DFA
TFA
359
382
467
469
3.05
3.01
ꢀ5.22
ꢀ5.19
ꢀ2.17
ꢀ2.18
122
129
426
408
a
Measured in tetrahydrofuran at a concentration of 1.0 ꢂ 10ꢀ5
.
b
c
d
e
f
Estimated from onset of the absorption spectra (Eg ¼ 1241/lonset).
The HOMO energy level was measured from cyclic voltammetry (EHOMO ¼ ꢀ4.4 - Eox).
The LUMO energy level was measured by the equation: ELUMO ¼ EHOMO þ Eg.
Measured by DSC curves.
Measured by TGA curves.
Fig. 3. Cyclic voltammograms of the three compounds in dichloromethane.
Fig. 5, and related data are summarized in Table 2. It can be seen
that, the turn-on voltages of these devices were small, which were
determined to be 2.9e3.6 V, meanwhile, the current density and
luminance of devices based on DFA and TFA are comparable to the
device based on NPB at the same driving voltage. Moreover, the
device based on TFA achieved a maximum luminance of 89475 cd/
m2 at 11 V.
From Fig. 6a), it can be seen that, the maximum current effi-
ciency of devices based on DFA, TFA and NPB were 31.26 cd/A,
41,68 cd/A and 29.92 cd/A, respectively, and the corresponding
maximum power efficiency were 22.76 lm/W, 32.04 lm/W and
29.64 lm/W. Fig. 6c) implied that the maximum external quantum
efficiencies were 8.86%, 12.04% and 8.70% for DFA, TFA and NPB
based devices, respectively. Fig. 6aec indicated that the efficiencies
roll-off phenomena of devices based on DFA and TFA are somewhat
alleviated comparing with NPB, which could be ascribed to the
better hole-transport characteristics of these two compounds and
more balanced charge combination properties of the DFA and TFA
Fig. 2. a). The thermogravimetric analysis (TGA) curves, the decomposition tempera-
tures (Td) corresponding to 5% weight loss; b) Differential scanning calorimetry (DSC)
curves of DFA and TFA.
2.5. EL performance
To investigate the hole-transporting properties of these two
triarylamine-based materials, OLEDs with the device structure of
[ITO/MoO3 (3 nm)/HTM (40 nm)/TCTA (10 nm)/CBP:Ir(ppy)3
(20 nm, 8 wt%)/TPBi (35 nm)/LiF (1 nm)/Al (200 nm)] were fabri-
cated using DFA or TFA as the hole-transport layer, ITO and LiF/Al
were employed as the anode and composite cathode, respectively.
MoO3, TCTA and TPBi acted as hole injection layer(HIL), electron
block layer(EBL) and electron transport layer(ETL), respectively. CBP
was played as host, and Ir(ppy)3 was used as the emitting material.
For comparison, the control device with configuration of [ITO/MoO3
(3 nm)/NPB (40 nm)/TCTA (10 nm)/CBP:Ir(ppy)3 (20 nm, 8 wt
%)/TPBi (35 nm)/LiF (1 nm)/Al (200 nm)] was also prepared. The
energy level diagram of these materials in as-prepared devices are
shown in Fig. 4.
The current density-voltage-luminance (I-V-L) characteristics of
these devices with various hole transport materials are shown in
Fig. 4. The energy level diagram of the materials in devices.

P. Wu et al. / Tetrahedron 73 (2017) 4610e4615
4613
Fig. 5. Current density-voltage-luminance (I-V-L) curves of devices based on DFA, TFA
and NPB.
Table 2
EL performance of devices based on NPB, DFA and TFA.
Compounds Von(V)a Lmax[cd/m2]b hc(cd/A)c hp(lm/W)c hext(%)c CIE(x,y)
d
NPB
DFA
TFA
2.9
3.1
3.6
51890
82530
89475
29.92
31.26
41.68
29.64
22.76
32.04
8.70
8.86
12.04
(0.44,0.28)
(0.31,0.62)
(0.31,0.61)
a
Turn-on voltage to give a luminance of 1 cd/m2.
Lmax: maximum luminance.
Maximum values. hc: current efficiency. hp: power efficiency. hext: external
b
c
quantum efficiency.
d
Measured form the EL spectra at 10 V by inverting chromaticity coordinates on
the CIE 1931 diagram.
based devices. Besides, the TFA-based device displays higher effi-
ciencies than the DFA-based device as a result of stronger electron
donating properties of triphenylamine moiety.
Fig. 7 showed the EL spectra of DFA and TFA based devices at
10 V. Emission at 516 nm and 512 nm respectively for DFA and TFA
based devices can be seen clearly, which correspond to the CIE
coordinates of (0.31, 0.62) and (0.31,0.61), respectively.
Hence, as revealed in Fig. 6 and Table 2, the devices based on
DFA and TFA exhibited better performance than NPB, which could
be attributed to the higher HOMO energy levels and excellent
thermal stability of DFA and TFA.
Fig. 6. a) current efficiency-current density curves; b) power efficiency-current den-
sity curves; c) external quantum efficiency-current density of devices based on DFA,
TFA and NPB.
3. Conclusion
To conclude, two novel hole transport materials based on
naphtho[2,1-b]benzofuran were synthesized and well character-
ized. The good thermal stabilities and suitable HOMO energy levels
of these two compounds allow them to be promising hole transport
materials. In the test of the EL performance, DFA- and TFA-based
devices showed better performance than NPB-based device. Espe-
cially, the TFA-based device exhibited the best performance with
the current efficiency, power efficiency and external quantum ef-
ficiency of 41.68 cd/A, 32.04 lm/W and 12.04%, respectively, which
proved that the introduction of naphtho[2,1-b]benzofuran can
enhance the thermal stability and hole transport ability of
triarylamine-based compounds. Thus, TFA will be a potential hole
transport material for commercial application in OLEDs.
Fig. 7. EL spectra at 10 V of DFA- and TFA-based devices.
Shanghai Taoe chemical technology Co., Ltd and used as received
without further purification. The 1H and 13C NMR spectra were
recorded on a Bruker AM 400 spectrometer at room temperature.
High resolution mass spectra were obtained by a Waters LCT pre-
mier XE spectrometer. The UVevis absorption spectra and Photo-
luminescence (PL) spectra were recorded on a Varian Cary 500
spectrophotometer and a Varian-Cary fluorescence spectropho-
tometer, respectively. The cyclic voltammograms of the compounds
were performed by a Versastat II electrochemical workstation using
a conventional three electrode configuration with a glassy carbon
4. Experimental section
4.1. General information
All chemicals and solvents of the route were purchased from

4614
P. Wu et al. / Tetrahedron 73 (2017) 4610e4615
working electrode, a Pt wire counter electrode, and a regular
calomel reference electrode in saturated KCl solution, 0.1M
Bu4NPF6 in dichloromethane solution as a supporting electrolyte.
Thermogravimetric analysis (TGA) were performed under a nitro-
gen atmosphere on a NETZSCH STA 409 PC/PG instrument and a
TGA instrument. The differential scanning calorimetry (DSC) anal-
ysis were measured on a DSC Q2000 instrument under a nitrogen
atmosphere.
4.2.4. Synthesis of N-([1,1'-biphenyl]-4-yl)-9,9-dimethyl-N-(4-
(naphtho[2,1-b]benzofuran-6-yl)phenyl)-9H-fluoren-2-amine (DFA)
A mixture of compounds 3 (0.3 g, 1.14 mmol), 1 (0.5 g,
0.97 mmol) and 2M aq.K2CO3 (10 mL) was stirred for 30 min under
nitrogen atmosphere. Tetrakis(triphenylphosphine)palladium
(0.023 g, 0.02 mmol) was added to the mixture, and the resulting
mixture was refluxed for 6 h under nitrogen atmosphere. After
cooling to room temperature, poured into H2O and then extracted
with dichloromethane. The combined organic phase was collected,
filtered and dried over MgSO4. The crude product was purified by
SiO2 column chromatography using petroleum ether/dichloro-
methane (4:1, v/v) afforded DFA (0.43 g, 68.0%). 1H NMR (400 MHz,
4.2. Synthesis
4.2.1. Synthesis of N-([1,1'-biphenyl]-4-yl)-N-(4-bromophenyl)-9,9-
dimethyl-9H-fluoren-2-amine (1)
CDCl3)
d
8.66 (d, J ¼ 8.6 Hz, 1H), 8.46 (d, J ¼ 8.9 Hz, 1H), 8.06 (d, 2H),
7.96 (d, J ¼ 8.6 Hz, 2H), 7.73 (dd, J ¼ 8.6, 5.2 Hz, 2H), 7.70e7.61 (m,
A mixture of N-([1,1'-biphenyl]-4-yl)-9,9-dimethyl-9H-fluoren-
2-mine (1.00 g, 2.77 mmol), 1-bromo-4-iodobenzene (1.00 g,
3,53 mmol), potassium hydroxide (0.30 g, 5.38 mmol), coprous
iodide (5.70 mg, 0.03 mmol) and 1,10-Phenanthroline monohydrate
(5.40 mg, 0.03 mmol) in ortho-xylene (30 mL) was stirred at 150 ꢁC
for 8 h under nitrogen atmosphere. After cooling to room temper-
ature, the solution was evaporated in vacuum. The cold water was
added to the mixture and finally extracted with DCM. The com-
bined organic phase was collected, filtered and dried over MgSO4.
The crude product was purified by SiO2 column chromatography
4H), 7.57 (d, J ¼ 8.6 Hz, 3H), 7.53e7.49 (t, 2H), 7.44 (dd, J ¼ 14.9,
7.2 Hz, 3H), 7.35 (m, 8H), 7.21 (d, J ¼ 8.2 Hz, 1H), 1.47 (s, 6H). 13
C
NMR (101 MHz, CDCl3)
d 154.75, 154.19, 152.57, 151.17, 146.67,
145.99, 145.76, 139.53, 137.85, 134.49, 133.74, 129.89, 129.07, 128.76,
128.16, 127.74, 127.19, 126.85, 125.97, 125.86, 125.81, 125.77, 125.65,
125.58,125.31,124.91,123.94,123.70,123.39,123.05,122.45,122.20,
121.47, 120.96, 119.75, 118.50, 118.29, 116.98, 111.04, 45.88, 26.08.
HRMS (ESI, m/z): [MþH]þ calculated for C49H36NO, 654.2797, found
654.2784.
using petroleum ether/dichloromethane (4:1, v/v) afforded
1
(1.31 g, 91.8%). 1H NMR (400 MHz, CDCl3)
d
7.58 (d, J ¼ 7.5 Hz, 1H),
4.2.5. Synthesis of N-(9,9-dimethyl-9H-fluoren-2-yl)-9,9-dimethyl-
7-(naphtho[2,1-b]benzofuran-6-yl)-N-phenyl-9H-fluoren-2-amine
(TFA)
7.52 (t, J ¼ 7.5 Hz, 3H), 7.43 (d, J ¼ 8.7 Hz, 2H), 7.35 (dd, J ¼ 15.4,
7.4 Hz, 3H), 7.29 (d, J ¼ 8.9 Hz, 2H), 7.23 (m, 3H), 7.14 (d, J ¼ 2.0 Hz,
1H), 7.10 (d, J ¼ 8.6 Hz, 2H), 6.98 (m, 3H), 1.36 (s, 6H).
TFA (0.45 g, 92.53%) was synthesized in a similar way of DFA
with 2 instead of 1. 1H NMR (400 MHz, CDCl3)
d
8.60 (d, J ¼ 8.2 Hz,
1H), 8.39 (d, J ¼ 9.0 Hz, 1H), 8.03 (d, J ¼ 5.2 Hz, 2H), 7.92 (d,
J ¼ 6.4 Hz, 2H), 7.76 (d, J ¼ 8.0 Hz, 1H), 7.65 (d, J ¼ 16.7 Hz, 2H), 7.54
(m, 5H), 7.44 (d, J ¼ 10.7 Hz, 2H), 7.32 (d, J ¼ 7.4 Hz, 1H), 7.23 (m,
6H), 7.16 (s,1H), 7.07e6.98 (m, 3H),1.46 (s, 6H),1.36 (s, 6H). 13C NMR
4.2.2. Synthesis of 7-bromo-N-(9,9-dimethyl-9H-fluoren-2-yl)-9,9-
dimethyl-N-phenyl-9H-fluoren-2-amine (2)
A
mixture of 9,9-dimethyl-N-phenyl-9H-fluoren-2-amine
(2.00 g, 7.02 mmol), 2,7-dibromo-9,9-dimethyl-9H-fluorene
(2.95 g, 8.43 mmol), potassium tert-butylate (1.56 g, 13.92 mmol),
palladium acetate (40.41 mg, 0.18 mmol) and 2-
(101 MHz, CDCl3)
d 154.78, 154.41, 153.99, 152.94, 152.47, 151.24,
138.06, 137.96, 133.36, 129.89, 128.21, 127.59, 127.31, 127.14, 126.36,
126.25, 125.95, 125.89, 125.41, 124.91,123.99,123.73,123.35,122.25,
122.20, 122.14, 121.79, 121.45, 120.98, 119.79, 119.57, 118.51, 118.36,
117.56, 117.15, 117.00, 111.08, 46.01, 45.79, 26.12, 26.02. HRMS (ESI,
m/z): [MþH]þ calculated for C52H40NO, 694.3110, found 694.3103.
dicyclohexylphosphino-20,40,6'-triisopropylbipheny
(0.16
g,
0.36 mmol) was dissolved in 1,3,5-trimethylbenzene (30 mL) and
heated at 170 ꢁC for 7 h under nitrogen. After cooling to room
temperature, the solution was evaporated in vacuum. The cold
water was added to the mixture and finally extracted with DCM.
The combined organic phase was collected, filtered and dried over
MgSO4. The crude product was purified by SiO2 column chroma-
tography using petroleum ether/dichloromethane (10:1, v/v)
Acknowledgements
Q. Dong acknowledges the financial support from the National
Natural Science Foundation of China (Grant No.: 61307030,
21402110). This work was also supported by the Program for the
Outstanding Innovative Teams of Higher Learning Institutions of
Shanxi (OIT), the Youth “Sanjin” Scholar Program, the Key R&D
Project of Shanxi Province (International cooperation program, No.
201603D421032), Fund Program for the Scientific Activities of
Selected Returned Overseas Professionals in Shanxi Province the
Outstanding Young Scholars Cultivating Program and Research
Project Supported by Shanxi Scholarship Council of China (Grant
No.: 2014-02).
afforded 2 (1.82 g, 46.8%).1H NMR (400 MHz, DMSO-d6)
d 7.77e7.73
(m, 3H), 7.69 (d, J ¼ 8.1 Hz, 1H), 7.53e7.49 (m, 2H), 7.38e7.22 (m,
7H), 7.14e7.08 (m, 3H), 6.99e6.95 (m, 2H), 1.36 (s, 12H).
4.2.3. Synthesis of naphtho[2,1-b]benzofuran-6-ylboronic acid (3)
A mixture of N,N,N0,N0-Tetramethylethylenediamine (4.68 g,
40.34 mmol) and dried tetrahydrofuran (100 mL) were added into a
three-necked flask under a nitrogen atmosphere and stirring for
15 min under ꢀ78 ꢁC, then 2.5M n-butyllithium (16.15 mL,
40.37 mmol) were added to the mixture by a disposable syringe and
continue to stirring for 30 min. Subsequently, naphtho[2,1-b]
benzofuran (8.00 g, 36.70 mmol) dissolved in tetrahydrofunan
(50 mL) were added dropwise to the reaction stirring for 2 h.
Finally, Boric Acid Triisopropyl Ester (18.74 mL, 80.73 mmol) were
added to the mixture and continue to reacting for 2 h and resulting
mixture was reacted overnight at room temperature. After cooling
to ambient temperature, the mixture was extracted with water and
dichloromethane, the organic layer was evaporated in vacuum
affording white solid 5 (9.2 g, 95.7%).1H NMR (400 MHz, CDCl3)
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.tet.2017.06.031.
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d
8.62 (d, J ¼ 8.3 Hz,1H), 8.50 (s,1H), 8.42 (m, J ¼ 9.0 Hz,1H), 8.11 (d,
J ¼ 8.2 Hz, 1H), 7.76 (m, 2H), 7.55 (m, 3H), 5.68 (s, 2H).

P. Wu et al. / Tetrahedron 73 (2017) 4610e4615
4615
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