Rational design and synthesis of 3-heteroaromatics coumarin molecules with unusual solution and solid dual efficient luminescence

Article abstract of DOI:10.1016/j.tet.2019.04.034

3-Imidazolyl coumarin molecules were synthesized under solvent-free condition and the optical properties both in solution and the solid state were determined. The compounds showed dual efficient luminescence, which were blue fluorescence with the highest fluorescence quantum yield being more than 0.9 and also exhibited favorable yellow solid-state fluorescence. Additionally, by using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculation, all structures were optimized and the associated optical performances showed similar results as the experimental results.

Full text of DOI:10.1016/j.tet.2019.04.034

Accepted Manuscript
Rational design and synthesis of 3-heteroaromatics coumarin molecules with unusual
solution and solid dual efficient luminescence
Zi-chun Zhou, An-na Zheng, Yan-hong Cui, Zhang-qi Lin, Wen-jie Niu, Yong-jian
Zhang, Jian-rong Gao, Yu-jin Li
PII:
S0040-4020(19)30446-6
https://doi.org/10.1016/j.tet.2019.04.034
TET 30279
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 2 February 2019
Revised Date: 9 April 2019
Accepted Date: 13 April 2019
Please cite this article as: Zhou Z-c, Zheng A-n, Cui Y-h, Lin Z-q, Niu W-j, Zhang Y-j, Gao J-r, Li Y-j,
Rational design and synthesis of 3-heteroaromatics coumarin molecules with unusual solution and solid
dual efficient luminescence, Tetrahedron (2019), doi: https://doi.org/10.1016/j.tet.2019.04.034.
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Rational design and synthesis of 3-
heteroaromatics coumarin molecules with
unusual solution and solid dual efficient
luminescence
Leave this area blank for abstract info.
Zi-chun Zhou, An-na Zheng, Yan-hong Cui, Zhang-qi Lin, Wen-jie Niu, Yong-jian Zhang, Jian-rong Gao, Yu-
jin Li*
College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, People's Republic of
China.

1
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Tetrahedron
journal homepage: www.elsevier.com
Rational design and synthesis of 3-heteroaromatics coumarin molecules with unusual
solution and solid dual efficient luminescence
Zi-chun Zhou, An-na Zheng, Yan-hong Cui, Zhang-qi Lin, Wen-jie Niu, Yong-jian Zhang, Jian-rong Gao,
Yu-jin Li*
College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, People's Republic of China.
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
3-Imidazolyl coumarin molecules were synthesized under solvent-free condition and the optical
properties both in solution and the solid state were determined. The compounds showed dual
efficient luminescence, which was blue fluorescence with the highest fluorescence quantum
yield being more than 0.9 and also exhibited favorable yellow solid-state fluorescence.
Additionally, by using density functional theory (DFT) and time-dependent DFT (TD-DFT)
calculation, all structures were optimized and the associated optical performances showed
similar results as the experimental results.
Available online
Keywords:
2
009 Elsevier Ltd. All rights reserved.
3
-imidazolyl coumarin
blue fluorescence
dual efficient luminescence
TD-DFT calculation
1
. Introduction
Coumarin dyes have attracted long-standing hotspot since
fluorescence in the solid state, which are well known as
13
aggregation-caused quenching (ACQ) owing to the formation
1
of molecular accumulation cause enhanced molecular π-π
they are considered with widely applications in various fields of
fundamental research, fluorescent probes, dye-sensitized solar
cells, transistors, and organic light-emitting diodes (OLEDs)
etc. In general, coumarin has been developed green to near-
infrared fluorescence by rigidifying with other fluorophores, such
as dihydropyridine, benzooxazole, naphthalene, BODIPY and
hemicyanine etc. However, the investigation of coumarin
fluorescent dyes with blue fluorescence is still quite limited,
14
stacking of the excited state. Accordingly, developing novel
2
coumarin dyes to solve the ACQ problem has been aggressively
studied.
3
4
5
In general, the introduction of electron withdrawing groups
at 3 positions and electron donating groups at 7 positions of
coumarin leads to form a "push-pull" structure, which can further
enhance the optical performance of coumarins by the
6
7
8
9
10
11
15
12
intramolecular charge transfer (ICT) mechanism. In order to
obtain high quantum yield of coumarin molecules, we designed
and synthesized imidazo[1,2a]pyridine substituted at the 3-
especially those exhibiting high quantum yield. Therefore,
developing new blue-emitting coumarin is very crucial.
Meanwhile, most coumarin derivatives exhibit extremely weak
Scheme 1. The synthesis of 2-acetylcoumarin 2 and 3-imidazolyl coumarin 3
∗
Corresponding author. Tel.: +86 0571 88320891; fax: +86 0571
8
8320544. E-mail address: lyjzjut@zjut.edu.cn (Y.j. Li).

2
Tetrahedron
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-
5
-1
Fig.1. Absorption spectra (left) and fluorescence spectra (right) of 3-NP1 (1×10 mol·L ) in
different solvents
position and diethylamino substituted at the 7-position of
coumarin derivatives. These coumarin derivatives have a
relatively smaller conjugate structure with higher quantum yield
than traditional coumarin fluorescence dyes. Herein, we
examined the optical properties of these fluorescent molecules
which showed blue fluorescence with high quantum yield and
yellow luminescence in solid state. Furthermore, the DFT and
TD-DFT calculation results are consistent the experimental
results.
Table 1
Optical data of 3-NP1 determined in different solvents at
room temperature.
Solvent
b
UV-Vis
Fluorescence
em(nm)
SS
-1
-1
a
F
λabs(nm)
ε(M ·cm )
λ
Ф
(nm)
toluene
DCM
407
429
425
407
408
421
425
428
424
423
52000
52000
46200
51500
50900
49300
51900
51300
44800
49000
469
478
471
468
473
475
477
482
482
485
0.83
0.86
0.93
0.70
0.65
0.82
0.67
0.61
0.75
0.71
62
49
46
61
65
54
52
54
58
62
CHCl
3
EA
THF
MeCN
DMF
DMSO
EtOH
MeOH
a
F
Fluorescence quantum yields (Ф ) are measured using an integrating sphere
method. Standard errors are less than 5%.
b
The Stokes shift of the experimental results.
2
2
.2. Fluorescence detection
-
5
-1
Fig.2. The color of 3-NP1(1×10 mol·L )(left to right:
.2.1. UV-Vis and fluorescence of 3-NP1 in solution
toluene, DCM, CHCl , EA, THF, MeCN, DMF, DMSO,
EtOH, MeOH) under visible light (upper row) and the UV
lamp (365 nm, lower row)
3
The absorption and fluorescence properties of compound 3-
NP1 were determined in different solvents and the results were
shown in Table 1. The absorption peaks of 3-NP1 in different
solvents was found in the range of 407-429 nm, whilst the
fluorescence emission peaks of 3-NP1 was exhibited blue
fluorescence at around 475 nm. As shown in Fig. 1 and Table 1,
2
. Results and discussion
2
.1. synthesis
4
preparation of the target fluorescent molecules 3 was shown
the molar absorption coefficient (ε) of 3-NP1 was about 5×10
in scheme 1. Precursors 3-acetylcoumarin 2 were accomplished
by the condensation reaction of salicylaldehyde derivatives with
ethyl acetoacetate catalyzed by piperidine which resulted in 80%
and the solvents had rarely effect on the absorption peaks.
However, the absorption spectra in chlorinated (DCM and
CHCl ) and polar solvents were subjected to a slight red shift of
3
(
R = H) and 71% (R = NEt ) yields, respectively. The target
around 14-22 nm. Meanwhile, the fluorescence emission peak of
3-NP1 was rarely affected by solvents, yet in the polar solvent it
was shown to decline slightly. The Stokes shift in different
solvents was about 40-60 nm. Additionally, it can be seen from
Table 1 that the 3-NP1 exhibited high fluorescence quantum
1
1
2
molecule 3-heteroaromatics coumarin derivatives were
synthesized by the [3+2] cycloaddition reaction of 3-
16
acetylcoumarin 2 and 2-aminopyridine catalyzed by iodine. 3-
Imidazo[1,2a]pyridine coumarin 3-HP, 3-NP1~3-NP3 were
yielded in 40-65% with the reaction of 3-acetylcoumarin and 2-
aminopyridine. 3-Imidazo[1,2a]quinoline coumarin 3-NQ was
yielded of 39% when 2-aminoquinoline was employed. All the
structures of 3-HP, 3-NP1, 3-NP2, 3-NP3 and 3-NQ were
yields (Ф
(methylbenzene (0.83), DCM (0.86) and MeCN (0.82)). It is
noteworthy that the Ф of 3-NP1 was the highest (0.93) in
chloroform. In contrast, the Ф were slightly reduced in the polar
solvents such as EA (0.70), THF (0.65), DMF (0.67) and DMSO
) which were higher than 0.8 in non-polar solvents
F
F
F
1
13
characterized by H NMR, C NMR analysis and HR-MS.

3
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-
5
-1
Fig.3. Absorption spectra (left) and fluorescence spectra (right) of compound 3 (1×10 mol·L ) in
CHCl3
Table 2
Optical data of compound 3 in CHCl3.
Dye
UV-Vis
Fluorescence
SS
-
1
-1
λabs(nm)
ε(M ·cm )
λem(nm)
Ф
F
(nm)
3
-HP
349
425
424
434
434
15200
46200
38000
41500
69800
456
471
473
478
460
0.15
0.93
0.94
0.90
0.92
107
46
49
42
26
3
-NP1
-
5
-1
Fig. 4. The color of compound 3 (1×10 mol·L ) in CHCl
3
3-NP2
-NP3
-NQ
under UV lamp (365 nm)
3
(0.61), while in ethanol and methanol (protonic solvents) were
3
0
.75 and 0.71, respectively. As shown in Fig.2, the color of 3-
NP1 in different solvents appeared as pale yellow under visible
light and blue under UV lamp (365 nm).
2
.2.2. optical properties of compound 3 in solvents
According to optical properties of 3-NP1 in different
solvents, the absorption and fluorescence spectrum of
compound 3 were measured in chloroform and the results
were shown in Fig. 3 and Table 2. The absorption peak of 3-
HP was found at 349 nm and its molar absorption coefficient
4
(
ε) was 1.5×10 . The fluorescence emission spectrum of 3-HP
corresponded to a emission peak at 456 nm. However, The 7-
diethylamine substituted coumarin molecules showed a
similar absorption peak at about 430 nm and the fluorescence
emission wavelength ranged from 460 to 478 nm. It can be
seen from Fig. 4 that the five compounds in chloroform
appeared as colorless or pale yellow under visible light and
were shown as blue fluorescence under UV radiation (365
nm). Due to the introduction of diethylamino group, the molar
absorption coefficient (ε) of compounds 3-NP and 3-NQ
greatly increased and the emission peaks were also
significantly enhanced. This can be explained by the fact that
a push-pull structure formed by the introduction of the 7-
position diethylamino group and the 3-position nitrogen
heterocycle, which caused the ICT to occur, and the ICT
resulted in an increase in the molar absorption coefficient and
Fig.5. Normalized fluorescence spectra of 3-HP, 3-NP1, 3-
NP2 and 3-NQ in the solid state.
2. It is worth nothing that substitution of the diethylamino group
greatly increased the fluorescence quantum yield from 0.15 (3-
HP) to more than 0.9 of 3-NP1, 3-NP2, 3-NP3 and 3-NQ with
diethylamine substituted on 7-position. However, the substituted
groups in the 3-heterocyclic ring were shown slightly influence
on the fluorescence quantum yield, suggesting that the
introduction of substituted groups in the 3-heterocyclic ring were
hardly influence the charge distribution in the molecule.
Furthermore, the Stokes shifts of 3-NP1, 3-NP2 and 3-NP3 were
all around 45 nm and due to the conjugate action of the benzene
ring, the Stokes shift of 3-NQ was reduced to 26 nm. Although
the fluorescence quantum yield of 3-HP was the lowest
1
7
the fluorescence performance.
The molar absorption
4
coefficient (ε) of 3-NQ was the highest of 7.0×10 . In the
fluorescence emission spectrum, the substitution of the
diethylamino group in the coumarin 7-position caused a slight
red shift of the emission wavelength from 456 to 475 nm.
Moreover, due to the growth of the conjugated system, the
emission wavelength of 3-NQ exhibited a slight blue shift to
4
60 nm. The fluorescence quantum yields of compound 3
(
Φ =0.15), 3-HP exhibited a large Stokes shift up to 107 nm.
F
with different substituent groups were also displayed in Table

4
Tetrahedron
2
.2.3. Optical Properties of compound 3 in the solid state
ACCEPTED MATa
N SCRIPT
ble
U
3
Optical data of compound 3 in the solid state.
Generally, the high planarity molecules may lead to π-π
stacking between molecules causing molecular accumulation
resulting in fluorescence quenching in the solid state. The
research of the solid-state fluorescence of coumarin compounds
Dye
UV-Vis
Fluorescence
em(nm)
SS
1
8
λex(nm)
λ
Ф
F
(nm)
19
has been reported rarely. It was an interesting phenomenon
opposite to ACQ that the compounds showed yellow
fluorescence in the solid state. Thus, we further observed solid-
state fluorescence properties of 3-imidazolyl coumarins with
different substituent groups. Photos of the color of compound 3
in the solid state were provided for comparison (Fig. 6). It can be
seen from Fig. 5 and Table 3 that the emission wavelength of 3-
imidazolyl coumarin 3 were in the range of 520-590 nm in the
solid state, which was subjected to a significant red shift
compared with the emission wavelength in solution. Moreover,
the Stokes shift was more than 100 nm, reaching a maximum of
3-HP
412
479
430
423
461
520
593
557
586
590
0.02
0.05
0.14
<0.01
0.21
108
114
127
163
129
3
-NP1
-NP2
3
3-NP3
-NQ
3
21
our fluorescent molecules. The ground state geometrical
configurations of compounds 3 were optimized by applying the
B3LYP/6-31G(d) basis sets in gas phase and the polarizable
continuum model (PCM) at the B3LYP/6-311+G(d, p) level in
CHCl3 . Then the absorption spectrum and emission spectrum
were calculated by TD-DFT on the corresponding basis sets. All
calculations were performed in the Gaussian 09 program
package . (Table 4). As can be seen in Table 4, both of the
calculated data in gas phase and CHCl were consistent the
experimental results, and the data in CHCl were more closer
1
63 nm. As shown in Table 3, the introduction of an electron-
2
2
donating diethylamino group was favorable for the solid-state
fluorescence properties of the coumarin molecules. In contrast, 3-
HP showed almost no solid-state fluorescence. It was obvious
that the introduction of different substituent groups into the
pyridine rings of 3-NP1, 3-NP2 and 3-NQ greatly influenced the
solid-state fluorescence of these compounds. The solid-state
fluorescence emission spectrum of methyl substituted 3-NP2 was
found at 557 nm which showed a fluorescence quantum yield of
2
3
3
3
with the experimental results. Moreover, it is closer to
experiments for the fact the experimental data was collected in
CHCl3.
0
.14, but the methoxy group substituted 3-NP3 did not exhibit
solid-state fluorescence due to the ACQ take place with the
substitution of methoxy group. In addition, the emission
spectrum of 3-NQ is at 590 nm with a rise in quantum yield to
20
The optimized geometry of 3-NP1 was shown in Fig. 7
which exhibited favorable planarity and a large conjugated
system in CHCl3.
0
.21 owing to extend of the conjugate system.
Fig.7. Representative optimized geometry of 3-NP1 in CHCl3
from different orientation at B3LYP/6-311+G(d, p) level
Fig.6. The color of compound 3 under visible light (upper
row) and UV lamp (365 nm, lower row)
2
.2.4. DFT calculation
The frontier molecular orbit and transition energy of
compound 3 in CHCl were shown in Fig. 8 and Table 4.
Through calculations, it was found that experimentally observed
To better understand the optical properties of the
compounds 3, DFT and TD-DFT calculations can be applied to
3
Fig.8. Representative HOMO and LUMO diagrams of compound 3 in CHCl obtained from
3
calculations and their corresponding energy levels at B3LYP /6-311+G(d, p) level

5
Table 4
Calculation and experimental data of compou
ACCEPTED MANUSCRIPT
nd
3
a
b
experimental
Dye
Calculation in gas phase
Calculation in CHCl
3
c
c
Energy gap
eV)
c
c
Energy gap
(eV)
λabs (nm)
λem (nm)
λ
abs (nm) / f
λem (nm) / f
λabs (nm) / f
λem (nm) / f
(
3
-HP
349
425
424
434
434
456
471
473
478
460
336 / 0.5255
380 / 0.9634
382 / 0.9541
388 / 0.8165
413 / 0.7924
361 / 0.6194
425 / 0.7135
440 / 0.5425
461 / 0.4239
430 / 1.0394
4.08
3.53
3.52
3.49
3.31
354 / 0.5205
422 / 1.2626
421 / 1.2611
424 / 1.2079
442 / 0.4900
384 / 0.6435
463 / 1.2857
468 / 1.2432
481 / 1.0770
466 / 0.9660
4.01
3.38
3.38
3.35
3.23
3
3
3
-NP1
-NP2
-NP3
3
-NQ
a
b
c
The calculated data in gas phase at the B3LYP/6-31G(d) level.
The calculated data in CHCl by employing polarizable continuum model (PCM) at the B3LYP/6-311+G(d, p) level.
Oscillator strength coefficients.
3
absorption/emission of 3-NP1, 3-NP2 and 3-NP3 were
corresponding to transitions from HOMO to LUMO, whilst 3-HP
and 3-NQ were corresponding to transitions from HOMO-1 to
LUMO. As shown in Fig. 8, the HOMO-1 electron cloud of 3-
HP was uniformly distributed in the whole molecule while the
electron cloud of LUMO concentrated on coumarin. It is known
that the electron donating group in the 7-position and electron-
withdrawing groups in the 3-position can be able to enhance the
fluorescence intensity of coumarin based on an intramolecular
charge transfer process(ICT). During the excitation, ICT
occurred to increase non-radiative energy, thus leading to a large
Stokes shift. It can also be seen that owing to the introduction of
the diethylamino group into 7-coumarin, the electron clouds of
HOMO-1 and LUMO in 3-NP1, 3-NP2, 3-NP3 and 3-NQ were
uniformly distributed in the whole molecule. Theoretical
calculations also confirm our previous conjecture that the
substituent group showed rarely influence on the charge
distribution in the molecules. It can explain why 3-NP1, 3-NP2,
fluorescence quantum yields were enhanced up to 0.9. In addition,
3-imidazolyl coumarin 3 showed yellow solid state emission at
520-590 nm. In particular, the fluorescence quantum yield of 3-
NQ determined by the integrated sphere are 0.92 in CHCl and
3
0.21 in the solid state, respectively. Besides, the absorption and
emission spectrum properities by TD-DFT calculation agreed
with the experimental spectrum. Such strategy of taking
advantages of ICT effect provided an effective method to
construct dual-state high-luminescent materials in both solution
and the solid state, which could be applied to the design of
OLEDs, live-cell imaging and fluorescent probes.
24
4
. Experimental
4
.1. Materials and equipment
All of the chemicals used in the current study were purchased
from commercial vendors and used as received without further
purification, unless otherwise noted. All solvents were purified
and dried using standard methods prior to use. Nuclear magnetic
3
-NP3 showed similar optical in solvent. As shown in Fig. 8, the
1
13
molecules of 3-NP1, 3-NP2, 3-NP3 and 3-NQ showed a larger
resonance ( H, C) spectra were recorded on a Bruker AM 500
spectrometer with chemical shifts reported as ppm at 500, 125
electron delocalization which is considered as a condition of
25
emission wavelength red shift and strong fluorescence intensity.
MHz, respectively (in CDCl and TMS as the internal standard).
3
The high-resolution mass spectra were recorded on a Thermo
Scientific LTQ Orbitrap XL (ESI) and melting points (m.p.) were
recorded on a X-4 electro-thermal digital melting point apparatus.
All of the chemicals used in the current study were purchased
from commercial vendors and used as received without further
purification, unless otherwise noted. All solvents were purified
and dried using standard methods prior to use.
According to the calculation optical data shown in Table 4,
the absorption wavelength of 3-HP in CHCl was 354 nm. Due
3
to the introduction of the diethylamino group, the absorption
wavelengths of 3-NP1, 3-NP2, 3-NP3 and 3-NQ have a red shift
of 67-88 nm in CHCl . Moreover, the emission wavelengths of 3-
3
NP1, 3-NP2 and 3-NP3 were subjected to a red shift from 463
nm to 481 nm in CHCl . In contrast, the emission wavelength of
3
3
-NQ displayed a slight blue shift to 466 nm. The theoretically
4
.2. Absorbance, fluorescence and quantum yield
calculated data showed similar as the experimental data (Table 1).
Additionally, the energy level of each compound was separately
calculated. 3-HP required 4.01 eV of energy when transition
from the HOMO-1 to the LUMO while the other four compounds
required a lower energy in the range of 3.23-3.38 eV and were
easier to transition compared with 3-HP. Accordingly, the
theoretically calculated results validated a factor leading to the
strong fluorescence of 3-NP1, 3-NP2, 3-NP3 and 3-NQ.
UV-Vis absorption spectra were measured on a UV-2550.
Fluorescence spectra were obtained with an Edinburgh FS5
spectrofluorometer. The solvents used in the photochemical
measurements were spectroscopic grade. All the experiments
were performed repeatedly, and reproducible results were
obtained. The Φ
values in solution were measured using an
F
integrating sphere method and dilute solutions of the compounds
-
5
-1
in organic solvent were used (1×10 mol·L ). The fluorescence
spectra were recorded 3 times. The solid emission spectra and ФF
were measured by attaching the solid samples on Edinburgh FS5
spectrofluorometer.
3
. Conclusion
In summary, we have developed novel blue fluorescence
coumarin derivatives containing imidazolyl on 3-position. The
fluorescent molecule 3-imidazolyl coumarins displayed
unusual solution and solid dual efficient luminescence, which
exhibited blue fluorescence at 470 nm in organic solvents and
yellow luminescence in the solid state. By the introduction of
diethylamine group at the 7-position of the coumarins, the
4
.3. General preparation of compound 3-acetylcoumarin
3
derivatives 2a-2b
A mixture of salicylaldehyde (10.0 mmol, 1.210 g), ethyl
acetoacetate (10.0 mmol, 1.270 g), piperidine(0.05 mL) in
ethanol (2.5 mL) was stirred to reflux for 4 h. The reaction was

6
Tetrahedron
complete detected by TLC and cooled to room
A
te
C
m
C
pe
E
ra
P
tu
T
re
E
, a
D
nd MA10
NU
9.24
S
(
C
2C
R
),
I
97.10 (1C), 44.88 (2C), 21.47 (1C), 12.52 (2C).
P
T
+ +
then the reaction precipitate was filtered to give the crude product.
The crude product was purified by re-crystallized from
anhydrous ethanol (5 mL) to afford target compound 2a (1.504 g,
HRMS (ESI): m/z calcd for C H N O [M+H] 348.1707,
21
22
3
2
found 348.1710.
4
.4.4. 7-(diethylamino)-3-(7-methoxyimidazo[1,2-a]pyridin-2-
8
0%) as white solid. 3-acetyl-2H-chromen-2-one (compound 2a)
1
yl)-2H-chromen-2-one (3-NP3).
white solid. Yield 80%. Mp 275-277 °C. H NMR (500 MHz,
CDCl ) δ(ppm): 8.52 (s, 1H), 7.70-7.63 (m, 2H), 7.36 (m, 2H),
1
3
Yellow solid. Yield 40%. Mp 235-236 °C. H NMR (500
2
.74 (s, 3H).
MHz, CDCl ) δ(ppm): 9.08 (s, 1H), 8.34 (s, 1H), 8.05 (d, J = 6.8
3
Hz, 1H), 7.59 (d, J = 8.7 Hz, 1H), 7.38 (s, 1H), 6.80 (d, J = 6.4
Hz, 1H), 6.65 (d, J = 7.9 Hz, 1H), 6.51 (s, 1H), 3.99 (s, 3H), 3.46
3
-acetyl-7-(diethylamino)-2H-chromen-2-one (compound
2
b) Yellow solid. Yield 71%. Mp 152-154 °C. (ref: 150-153 °C)
H NMR (500 MHz, CDCl ) δ(ppm): 8.73(s, 1H), 7.17(d, 1H),
.57(dd, 1H), 6.56(d, 1H), 3.33(q, 4H), 2.76(s, 3H), 1.23(t, 6H).
1
(
dd, J = 14.0, 7.0 Hz, 4H), 1.24 (t, J = 7.0 Hz, 6H). HRMS (ESI):
3
+ +
26
m/z calcd for C H N O [M+H] 364.1656, found 364.1657.
6
21 22
3
3
4
.4.5. 7-(diethylamino)-3-(imidazo[1,2-b]isoquinolin-2-yl)-2H-
4
.4. General preparation of compound 3
chromen-2-one (3-NQ)
A mixture of 2a (0.92 mmol, 0.1740 g), 2-aminopyridine (2.1
1
Yellow solid. Yield 39%. Mp 259-261 °C. H NMR (500
MHz, CDCl ) δ (ppm): 11.54 (s, 1H), 8.84 (s, 1H), 8.58 (d, J =
mmol, 0.1974 g) and iodine (1.0 mmol, 0.254 g) was stirred for 2
h at 110 °C, and then stirred for another 12 h at 80 °C. The
residue was diluted with 2 mL of distilled water and added
excess of 0.1 mL aqueous sodium hydroxide (45%). Then the
reaction mixture was stirred at 100 °C for 30 min. After cooling
to room temperature, the reaction mixture was diluted with 25
mL of DCM and added 10% aqueous HCl to the mixture until a
neutral pH. The mixture was then extracted with DCM (30
mL×3), and the organic layer was washed with water, and dried
with Na SO , and concentrated under reduced pressure. The solid
3
8
7
2
.9 Hz, 1H), 8.20 (d, J = 9.0 Hz, 1H), 7.97 (d, J = 8.4 Hz, 1H),
.80 (d, J = 7.3 Hz, 1H), 7.68 (t, J = 7.7 Hz, 1H), 7.52-7.43 (m,
H), 6.70 (dd, J = 9.0, 2.5 Hz, 1H), 6.57 (d, J = 2.3 Hz, 1H), 3.50
q, J = 7.2 Hz, 4H), 1.28 (t, J = 7.1 Hz, 6H). C NMR (126 MHz,
CDCl ) δ(ppm): 162.52 (1C), 158.10(1C), 153.07 (1C), 151.91
13
(
3
(
1C), 151.29 (1C), 148.88 (1C), 138.12 (1C), 135.85 (1C),
1
1
1
31.49 (1C), 129.69 (1C), 128.08 (1C), 127.37 (1C), 126.39 (1C),
25.10 (1C), 125.03(1C), 115.10 (1C), 110.18 (1C), 109.86 (1C),
08.64 (1C), 96.78 (1C), 45.22 (2C), 12.46 (2C). HRMS (ESI):
2
4
was isolated by column chromatography (silica, ethyl
acetate/petroleum ether 1:1 to dichloromethane/petroleum ether
+
+
m/z calcd for C H N O [M+H] 384.1707, found 384.1709.
24 22
3
2
3
:1) to afford dark yellow solid 3-HP (0.1063 g，43%).
Acknowledgments
4
.4.1. 3-(imidazo[1,2-a]pyridin-2-yl)-2H-chromen-2-one (3-HP).
This work was supported by the Natural Science Foundation
of China (21606201), the National Natural Science Foundation of
Zhejiang (LY13B020016) and the Undergraduate Science and
Technological Innovation Program in Zhejiang Province
1
Dark yellow solid. Yield 43%. Mp 207-209 °C. H NMR
(500 MHz, CDCl ) δ(ppm): 8.80 (s, 1H), 8.57 (s, 1H), 8.16 (d, J
3
=
7
6.7 Hz, 1H), 7.65 (d, J = 7.5 Hz, 1H), 7.60 (d, J = 9.1 Hz, 1H),
(Zhejiang Xinmiao Talents Program) (2017R403066).
.54 (t, J = 7.8 Hz, 1H), 7.39 (d, J = 8.3 Hz, 1H), 7.32 (t, J = 7.5
13
Hz, 1H), 7.25-7.18 (m, 1H), 6.81 (t, J = 6.7 Hz, 1H). C NMR
References
(126 MHz, CDCl ) δ(ppm): 159.99 (1C), 153.10 (1C), 145.15
3
(
1
1
1C), 138.30 (1C), 138.03 (1C), 131.32 (1C), 128.31 (1C),
26.20 (1C), 125.74 (1C), 124.67 (1C), 120.95 (1C), 119.72 (1C),
17.18 (1C), 116.42 (1C), 113.90 (1C), 112.56 (1C).
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.4.2.
7-(diethylamino)-3-(imidazo[1,2-a]pyridin-2-yl)-2H-
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.
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Dark yellow solid. Yield 54%. Mp 185-187 °C. H NMR
(
=
7
1
6
500 MHz, CDCl ) δ(ppm): 8.66 (s, 1H), 8.46 (s, 1H), 8.12 (d, J
6.7 Hz, 1H), 7.57 (d, J = 9.1 Hz, 1H), 7.42 (d, J = 8.8 Hz, 1H),
.21-7.13 (m, 1H), 6.76 (t, J = 6.6 Hz, 1H), 6.63 (d, J = 8.8 Hz,
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(
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4
29.44 (1C), 125.96 (1C), 125.09 (1C), 116.80 (1C), 113.76 (1C),
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.4.3. 7-(diethylamino)-3-(7-methylimidazo[1,2-a]pyridin-2-yl)-
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1
Dark yellow solid. Yield 65%. Mp 214-217 °C. H NMR
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3
=
=
6.9 Hz, 1H), 7.42 (d, J = 8.8 Hz, 1H), 7.32 (s, 1H), 6.60 (ddd, J
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