Isatin-phenylhydrazone dyes and boron complexes with large Stokes shifts: Synthesis and solid-state fluorescence characteristics

Article abstract of DOI:10.1016/j.tet.2015.03.115

Isatin-phenylhydrazone derivatives and their corresponding BF₂-complexes were efficiently synthesized by a three-step reaction starting from isatin and phenylhydrazine hydrochloride. The optical properties of these isatin-phenylhydrazone derivatives and their difloroboron complexes were investigated in different organic solvents and in the solid-state. Although these fluorescent dyes exhibit feeble fluorescent intensity in solution-state, high fluorescent intensity can be detected in their solid-state. The Stokes shift of these dyes can be achieved 95-198 nm versus the typical BF₂-complexes (ca. 15 nm) in the solid-state, which were caused by the remarkable geometry relaxation upon photoexcitation and its substantial effect on the energy levels of molecular orbitals. Information supporting this inference was supported by the density functional theory calculations.

Full text of DOI:10.1016/j.tet.2015.03.115

Accepted Manuscript
Isatin-phenylhydrazone dyes and Boron complexes with large Stokes shifts:
Synthesis and Solid-State Fluorescence characteristics
Jie Zheng, Yujin Li, Yanhong Cui, Jianhong Jia, Qing Ye, Liang Han, Jianrong Gao
PII:
S0040-4020(15)00455-X
10.1016/j.tet.2015.03.115
TET 26597
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 4 December 2014
Revised Date: 17 March 2015
Accepted Date: 30 March 2015
Please cite this article as: Zheng J, Li Y, Cui Y, Jia J, Ye Q, Han L, Gao J, Isatin-phenylhydrazone dyes
and Boron complexes with large Stokes shifts: Synthesis and Solid-State Fluorescence characteristics,
Tetrahedron (2015), doi: 10.1016/j.tet.2015.03.115.
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ACCEPTED MANUSCRIPT
Graphical Abstract
Isatin-phenylhydrazone dyes and Boron complexes with large Stokes shifts:
Synthesis and Solid-State Fluorescence characteristics
Jie Zheng, Yujin Li*, Yanhong Cui, Jianhong Jia, Qing Ye, Liang Han, Jianrong
Gao**
College of Chemical Engineering, Zhejiang University of Technology, Hangzhou, 310014, P. R.
China
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
900
800
700
600
500
400
300
200
100
0
111 nm
184 nm
400
450
500
550
600
650
700
750
800
wavelength/nm
1

ACCEPTED MANUSCRIPT
Isatin-phenylhydrazone dyes and Boron complexes with
large Stokes shifts: Synthesis and Solid-State Fluorescence
characteristics
Jie Zheng, Yujin Li*, Yanhong Cui, Jianhong Jia, Qing Ye, Liang Han, Jianrong
Gao**
College of Chemical Engineering, Zhejiang University of Technology, Hangzhou, 310014, P. R.
China
Corresponding authors.
E-mail addresses: lyjzjut@zjut.edu.cn (Y. Li).
Telephone number: +86-0571-88320891 (Y. Li).
ABSTRACT
Isatin-phenylhydrazone derivatives and their corresponding BF2-complexes were
efficiently synthesised by a three-step reaction starting from isatin and
phenylhydrazine
hydrochloride.
The
optical
properties
of
these
isatin-phenylhydrazone derivatives and their difloroboron complexes were
investigated in different organic solvens and in the solid-state. Although these
fluorescent dyes exhibit feeble fluorescent intensity in solution state, high fluorescent
intensity can be detected in their solid-state. The Stokes shift of these dyes can be
achieved 95~198 nm vs the typical BF2-complexes (ca. 15 nm) in the solid-state
which were caused by the remarkable geometry relaxation upon photoexcitation and
its substantial effect on the energy levels of molecular orbitals. Information
supporting this inference was supported by the density functional theory calculations.
Keywords: boron complexes; large Stokes shift; solid state; geometry relaxation.
2

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1. Introduction
Difluoroboron complex fluorescent dyes exhibit high fluorescence quantum yield,
excellent photostability, and sharp fluorescence spectra in solution1 as a multipurpose
fluorophore which makes they have drawn much attention in luminophores2
molecular probes or molecular logic gates3 light-harvesting molecular arrays4
photodynamic therapy (PDT)5 and more recently, triplet-triplet annihilation (TTA)
upconversions, etc.6,7 However, most boron complexes hardly fluoresce in the solid
state because of the significant aggregation-caused quenching (ACQ) effect.8
Meanwhile, the small Stokes shift (ca. 15 nm) has never been addressed also
contribute another remarkable disadvantage for the boron complexes9,10 which often
have detrimental effects to its applications like in photoelectric conversion and
electroluminescence materials11 due to the emission intensity reduced by
self-absorption, or the inner filter effect.11b,c Thus, the boron complexes need to be
decorated for the long emission and large Stokes shift in order to avoid ACQ effect for
they can be used in broader fields such as field-effect transistors,12 live-cell imaging,13
organic light-emitting diodes (OLEDs)14 and fluorescent sensors.15
In order to address the long emission and the large Stokes shift of the boron
complexes, we designed a series of new boron complexes (BODIHY) that show solid
fluorescence and intrinsic large Stokes shift. These compounds show faint
fluorescence in solutions, but are induced to emit intensely with the aggregate
formation and the solid-state. It is noteworthy that the Stokes shift can be up to 198
nm, with excitation at green (ca. 496 nm) and emission at red (ca. 694 nm) in the solid
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state. Herein, we describe the synthesis and optical properties of the BODIHY
derivatives. Density functional theory (DFT) and time-dependent DFT (TDDFT)
calculations have been carried out to explore the reason for the large Stokes shift of
these compounds.
2 Results and discussion
2.1. Synthesis
Preparation of the substituted isatin-phenylhydrazone derivatives (precursor 2)
and their corresponding boron complexes (BODIHY 3) is shown in Scheme 1. The
N-alkylation isatin was accomplished by the reaction of isatin and alkyl bromide in
the presence of K2CO3 (1.4 equiv.) with DMF as the solvent at room temperature. The
precursor 2 was prepared by the condensation of the isatin derivative (1 equiv.) with
phenylhydrazine hydrochloride (1 equiv.) in DMF at room temperature which resulted
in good yield. The BODIHY 3 was produced, with a yield of 64% (3a), 92% (3b),
78% (3c) yield, by using an excess of BF3·OEt2 in DCM with Et3N as the base and
purification by column chromatography (silica gel, ethyl acetate: petroleum ether =
1:10). The structures of the boron complex target products 3 were characterised by
FT-IR, 1H NMR, 13C NMR, 19F NMR, and HRMS analysis, except for the compounds
3a, 3b, and 3c that are too insoluble to record a carbon NMR spectrum.
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Scheme 1. The synthesis of the precursor 2 and the BODIHY 3.
2.2. Fluorescence properties
The fluorescence properties of phenylhydrazone derivatives (2a-2j) and their
corresponding boron complexes (3a-3j) were examined in different organic solvents
(Fig. 1) and in their solid-states (Fig. 2). The quantum chemical calculations of the
compounds 2d, 2e, 2f, 2g, 3d, 3e, 3f, and 3g at the ground state (S0 state) and the
compound 3d at the first excited state (S1 state) were optimized in Fig. 5 and Fig. 6.
Optical data in the solution and the solid-state for all compounds are gathered in Table
1.
2.2.1. Fluorescence in solution
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2a
CHCl3
2b
3.0
2c
b
0.6
0.5
0.4
0.3
0.2
0.1
0.0
DCM
EtOH
MeCN
THF
a
3a
3b
2.5
3c
2c
3d
3c
2.0
2d
3a
3b
1.5
1.0
0.5
0.0
2b
2a
350
400
450
500
550
600
350
400
450
500
550
600
wavelength/nm
wavelength/nm
Fig. 1. (a) Absorption spectra of compound 2a, 2b, 2c, 3a, 3b and 3c (10 ꢀM) in CHCl3. (b) Absorption spectra of
compound 2d (dotted) and 3b (plain) (100 ꢀM) in different solution.
As shown in Fig. 1 and Table 1, the precursor 2 (2a, 2d, 2g, and 2h) with the
phenyl showed a sharp absorption peak at approximately 400 nm, the precursor 2 with
the p-methoxyphenyl (2b, 2e, and 2i) or p-nitrophenyl (2c, 2f, and 2j) on the arene
showed the absorption peak at approximately 425 nm. The maximum absorption
wavelength (λmax) of BODIHY 3 (phenyl 3a, p-methoxyphenyl 3b, p-nitrophenyl 3c)
(437 nm, 455 nm, 449 nm) was more bathochromic than the corresponding precursor
2 (phenyl 2a, p-methoxyphenyl 2b, and p-nitrophenyl 2c) (400, 425, and 425 nm).
Moreover, the result also showed that it had rarely effect on the maximum absorption
peak of the BODIHY 3 and precursor 2 with the different substituent on the N-atom
of isatin ring (2a, 2d, 2h, 3a, 3d, and 3h) (Table 1). As shown in Fig. 1 (b), the λmax of
these compounds were barely affected by solvent polarity, suggesting that the dipole
moments of the molecules in their ground and excited states were almost equal.16 The
molar absorption coefficient (ε) of BODIHY 3 underwent a slight change in different
organic solvents (Fig. 1, Table 1) and the BODIHY 3 and precursor 2 which with the
p-nitro substituted on phenyl ring had the largest value. However, the precursor 2 and
BODIHY 3 hardly exhibited fluorescence in the different organic solvents which
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could not be detected and the fluorescence quantum yields (Φf) of these compounds
were below 1.00 % in the solution.
Table 1. Optical data of the precursor 2 and the BODIHY 3.
λe(max)
(nm)
409
450
427
490
425
495
402
485
421
495
420
484
403
489
396
470
427
506
423
500
437
495
452
496
449
503
437
500
455
503
449
496
437
498
437
493
ε
λeem(max) Φf Height
ꢀ
dye
2a
R1
R2
Matrix
(M-1.cm-1)
(nm)
(%)
(nm)
H
H
DCM
solid
18690
578
4191
2083
128
132
2b
2c
2d
2e
2f
H
H
MeO DCM
solid
20740
50400
21670
20800
41100
19260
21500
24200
26400
32900
21600
39400
26590
26000
54500
23220
17900
622
NO2
DCM
solid
DCM
solid
Et
Et
Et
Bz
H
598
628
3918
667
113
133
MeO DCM
solid
NO2
DCM
solid
DCM
solid
DCM
solid
2g
H
584
574
614
1296
95
2h 4-tBu-Bz
H
4.62 3018
104
111
2i 4-tBu-Bz MeO DCM
solid
3.28
< 1
826
2j 4-tBu-Bz NO2
DCM
solid
DCM
solid
3a
3b
3c
3d
3e
3f
H
H
H
636
694
616
646
664
622
632
656
1503
312
141
198
113
146
161
126
134
163
MeO DCM
solid
H
NO2
DCM
solid
DCM
solid
3309
1820
354
Et
Et
Et
Bz
H
MeO DCM
solid
NO2
DCM
solid
DCM
solid
DCM
solid
1908
6526
732
3g
H
3h 4-tBu-Bz
H
6.10
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3i 4-tBu-Bz MeO DCM
456
500
450
500
19700
36700
solid
684
624
2.01
475
184
124
3j 4-tBu-Bz NO2
DCM
solid
9.12 2428
λe: λabs for solution-state absorption or λexc for solid-state excitation of the experimental results; ε:.the molar
absorption coefficient in DCM; λeem: the emission spectra in the solid-state of the experimental results; ꢁ: the
Stokes shift in the solid-state of the experimental results; ΦF: quantum yields in the solid-state, recorded in KBr
pellets; Height: the intensity of the fluorescence in the solid.
2.2.2. Fluorescence in the solid-state
2a
2b
5000
2c
3a
3b
4000
3000
2000
1000
0
3c
2a
3c
3a
2b
3b
2c
500
550
600
650
700
750
800
wavelength/nm
Fig. 2. Fluorescence emission spectra of the precursor 2 (dotted) (λex = 450 nm, 490 nm, 495 nm, 2a, 2b, 2c) and
the BODIHY 3 (plain) (λex = 495 nm, 496 nm, 503 nm, 3a, 3b, 3c) in the solid-state (PMT Voltage: 600V).
Further, the fluorescence emission spectra of the BODIPY 3 and precursor 2 in
the solid-state were measured. As shown in Fig. 2, the BODIHY 3 (phenyl 3a,
p-methoxyphenyl 3b) had a red shift (36-83 nm) compared with the corresponding
precursor 2, for example, 2a at 578 nm and 3a at 636 nm, 2b at 622 nm and 3b at 694
nm (Table 1), and the intensity of the fluorescence of the BODIHY 3 with the
p-nitrophenyl (3c) was much stronger than the corresponding precursor 2 (2c). The
colour of compounds 2a, 2b, 2c, 2h, 2i, 2j, 3a, 3b, 3c, 3h, 3i, and 3j in their solid
state by direct visualization and UV lamp (365 nm) are shown in Fig. 3 and it also can
intuitively indicated this result. This interesting phenomenon is opposite to ACQ
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effect widely observed from conventional chromophores and this aggregation-induced
emission enhancement (AIEE) phenomenon have been discussed in another paper.17
Fig. 3. The colour of compounds 2a, 2b, 2c,2h, 2i, 2j, 3a, 3b, 3c, 3h, 3i, and 3j in the solid-state.
2.2.3. Large Stokes shift and the fluorescence quantum yield in the solid-state
As shown in Fig. 4 and table 1, both the precursor 2 and the BODIHY 3 have
the large Stokes shifts which between about 95 and 198 nm in the solid-state. The
maximum Stokes shift of 3b was up to 198 nm, with excitation at green (ca. 496 nm)
and emission at red (ca. 694 nm) in the solid-state. In order to investigate the effect of
substituent group, a series of the precursor 2 and the BODIHY 3 with different
substituent on the arene and the N-atom of the isatin ring were synthesized.
Interestingly, the complexes with the different substituent on the arene change largely
in the emission spectra and the Stokes shift while rarely effect can be detected with
the substituent the N-atom of the isatin ring. Therefore, we chose a series of
compounds 2 (2h, 2i, and 2j) and 3 (3h, 3i, and 3j) with the different substituent on
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the arene to represent for the precursor 2 and the BODIHY 3 to determine the Φf in
the solid-state. The Φf of the compounds (2h, 2i, 2j, 3h, 3i, and 3j) in the solid-state
was examined as 4.62 %, 3.28 %, <1.00%, 6.10 %, 2.01 %, and 9.12 %, respectively.
For the precursor 2 (2a, 2d, 2g, and 2h) which with the phenyl have the largest value
of the Φf among the precursor 2. The precursor 2 (2b, 2e, and 2i) and the BODIHY 3
(3b, 3e, and 3i) with the electron-donating group (OMe) on the arene all have the
longer wavelength in the fluorescence emission spectra, and also have the larger
Stokes shifts. Therefore, the electron-donating group is beneficial to the Stokes shifts
of these compounds. The effect of the electron-withdrawing group (NO2) was
dramatically different for the precursor 2 and the BODIHY 3, the precursor 2 (2c, 2f,
and 2j) with the NO2 the intensity of the fluorescence largely reduced and almost
quenched in the solid-state, while the intensity of the fluorescence of the BODIHY 3
(3c, 3f, and 3j) increased to be the strongest one and has the largest Φf among all the
compounds. Accordingly, on balance the Φf of the BODIHY 3 was better than the
precursor 2 with the same substituent.
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
900
800
700
600
500
400
300
200
100
0
111 nm
184 nm
400
450
500
550
600
650
700
750
800
wavelength/nm
Fig.4. Absorption (plain) and emission (dotted) spectra of 2i (black) and 3i (red) in the solid-state.
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2.2.4. Quantum chemical calculations
To better understand the photophysical properties of the precursor 2 and the
BODIHY 3, such as the UV-vis absorption and fluorescence, especially the large
Stokes shift, the geometry of the compounds 2d, 2e, 2f, 2g, 3d, 3e, 3f, and 3g at the S0
state and the S1 state were optimized by density functional theory (DFT) and
time-dependent DFT (TDDFT) methods, respectively. Revealing the photophysical
properties from a theoretical perspective will be useful for the design of the
substituted isatin-phenylhydrazone derivatives and their corresponding boron
complexes. TD-DFT calculations have been performed at the B3LYP/6-31G(d) level
of theory,18 as implemented in the Gaussian 09 program package.19 All the
calculations were performed with the three-parameter functional Beche and the
correlation functional of Lee et al. According to the calculated results, the UV-vis
absorption spectra were simulated by Gaussian functions with the full width at
half-maximum of 0.33 eV.
Table 2. The absorption spectra of 2d, 2e, 2f, 2g, 3d, 3e, 3f, and 3g of the experimental and
calculated results.
dye
2d
2e
2f
2g
3d
3e
3f
3g
λe (max) (nm)
λt (max) (nm)
485
392
495
405
484
420
489
393
500
398
503
429
496
413
498
399
eThe solid-state excitation of the experimental results. tThe calculated absorption.
The calculated absorption peaks of the 3d, 3e, and 3f are located at 398, 429, and
413 nm, respectively (Table 2), which are consistent with the experimental results of
500, 503, and 496 nm. And the effect of the substituent group to the compounds was
agreed with the experimental results. As shown in the Fig. 5, the energy gap between
the HOMO and LUMO of the BODIHY 3 is 3d (phenyl) (3.35 eV), 3e (p-nitrophenyl)
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(3.15 eV), and 3f (p-methoxyphenyl) (3.24 eV), respectively.
Fig. 5. Molecular orbital amplitude plots of HOMO and LUMO energy levels of 3d, 3e and 3f.
In order to further research the large Stokes shift, the S1 excited state was
calculated represented by the compound 3d. The calculated emission peak is 509 nm
and the Stokes shift of the calculation is 111 nm. The calculated results were in
agreement with the experimental results (146 nm). The geometry of the S1 excited
state which is responsible for the fluorescence (Kasha’s rule)20 is different from the S0
state geometry (Fig. 6). The bond length of the N3-C24 in the S1 is 1.377 Å much
shorter than that in the S0 (1.428 Å). The phenyl moiety and the BODIHY core are
coplanar in the S1 state with the dihedral angles was only 0.55° compared with that in
the S0 state (25.82 °). The geometry relaxation upon photoexcitation imparts
remarkable effect on the energy level of the molecular orbitals. 20 For example, the
LUMO is stabilized by 0.47 eV at the S1 state geometry compared to that at the S0
state geometry, but the HOMO is destabilized by 0.28 eV for S1 state geometry
compared to that at the S0 state geometry. As a result, the energy gap between the
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LUMO and HOMO is greatly decreased with geometry relaxation at the S1 state
compared to that at S0 state geometry (UV-vis absorption, i.e., excitation). Thus, we
propose that the geometry relaxation is the main origin of large Stokes shift for the
compound 3d, which is in agreement with the Jablonski diagram of the
fluorescence.21
Fig. 6. The geometry of compound 3d in the s0 state (left) and in the s1 state (right).
3. Conclusion
In conclusion, a new family of BF2-Hydrazone derivatives (3) containing
isatin-phenylhydrazone were developed that showed enhanced fluorescence in the
solid-state. These compounds exhibit weak luminescence in solution, but are highly
emissive in the solid-state. All these compounds have large Stokes shift range from 95
to 198 nm. The geometries of the molecules at the S0 state and the S1 excited state
were optimized by DFT and TDDFT, respectively. The result of the calculation of the
UV-vis absorption is in agreement with the experimental result. The geometry
relaxation is proposed the primary cause for the large Stokes shift of the precursor 2
and the BODIHY 3. These series of compounds could be applied to the design of
OLEDs, live-cell imaging and fluorescent sensors.
4. Experimental
4.1 General
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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. Fourier
transform-infrared (FTIR) spectra were performed using Thermo Nicolet 6700
spectrophotometer. Nuclear magnetic resonance (1H, 13C, and 19F NMR) spectra were
recorded on a Bruker AM 500 spectrometer (Bruker) with chemical shifts reported as
ppm at 500, 125 and 376 MHz, respectively, (TMS as internal standard). Fluorescence
spectra were obtained with a F-7000 Fluorescence Spectrophotomete at solid state
with PMT Voltage at 600V. UV-Vis absorption spectra were measured on a UV-2550 .
4.2 Preparation of compounds 2a-2j
A mixture of isatin (1.4722 g, 10.0 mmol), ethyl bromide (1.0905 g, 10.0 mmol)
and anhydrous K2CO3 (2.0 g, 14.5 mmol) in DMF (10 mL) was stirred vigorously for
12 h at room temperature and complete reaction was detected by TLC analysis. The
reaction mixture was poured into water (100 mL) and the precipitate was concentrated
to give crude product 1a and recrystallized from EtOH.22 A mixture of 1a (0.8755 g,
5.0 mmol), phenylhydrazine hydrochloride (0.7325 g, 5.0 mmol) in DMF (10 mL)
was stirred vigorously at room temperature overnight. The reaction mixture was
poured into water (100 mL) and extracted with ethyl acetate (3 * 20 mL). The
combined organic layer was dried with MgSO4 and the solvent was removed under
reduced pressure. The residue was purified by silica gel chromatography eluting
(silica gel, ethyl acetate: petroleum ether = 1:5) leading to phenylhydrazone derivative
2d as a yellow solid.23
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4.2.1. 1H-indole-3-phenylhydrazone (compound 2a). Yellow solid. Yield 92%. Mp
210-213 °C. 1H NMR (500 MHz , CDCl3): δ=12.73 (s, 1H), 7.67 (d, 2H, J=7.4 Hz),
7.40-7.38 (m, 4H), 7.28-7.23 (m, 1H), 7.14-7.07 (m, 2H), 6.92 (d, 1H, J=7.8 Hz). 13C
NMR (125 MHz , CDCl3): δ=163.57 (1C), 142.64 (1C), 138.15 (1C), 129.46 (2C),
128.10 (1C), 126.86 (1C), 123.42 (1C), 122.69 (1C), 122.24 (1C), 119.24 (1C),
114.52 (2C), 110.21 (1C). FTIR (KBr, cm-1) 3166.0, 3057.2, 2922.3, 1681.8, 1597.0,
1556.7, 1493.0, 1463.7, 1345.5, 1296.4, 1246.2, 1171.0, 1101.2, 992.9, 859.3, 788.3,
748.8, 691.3, 628.7, 549.1, 493.4, 445.1. HRMS (ESI): calcd for C14H12N3O, [M +
H]+ 238.0980, found 238.0975.
4.2.2. 1H-indole-3-(4-methoxyphenyl)hydrazone (compound 2b). Deep-yellow solid.
Yield 85%. Mp 185-187 °C. 1H NMR (500 MHz , CDCl3): δ=12.77 (s, 1H), 7.79 (s,
1H), 7.65 (d, 1H, J=7.6 Hz), 7.35-7.34 (m, 2H), 7.24-7.21 (m, 1H), 7.13-7.10 (m, 1H),
6.95-6.91 (m, 3H), 3.84 (s, 3H). 13C NMR (125 MHz , CDCl3): δ=163.70 (1C),
156.37 (1C), 137.83 (1C), 136.48 (1C), 127.57 (1C), 125.82 (1C), 122.52 (1C),
122.41 (1C), 118.85 (1C), 115.79 (2C), 114.93 (2C), 110.17 (1C), 55.67 (1C). FTIR
(KBr, cm-1) 3165.2, 3057.0, 2830.5, 1674.7, 1618.6, 1592.7, 1552.6, 1519.4, 1463.1,
1388.6, 1343.3, 1299.6, 1230.2, 1175.0, 1106.2, 1040.0, 992.3, 889.7, 864.5, 822.9,
785.2, 746.5, 676.6, 538.8, 450.9. HRMS (ESI): calcd for C15H14N3O2, [M + H]+
268.1086, found 268.1081.
4.2.3. 1H-indole-3-(4-nitrophenyl)hydrazone (compound 2c). Deep-yellow solid.
Yield 92%. Mp 301-303 °C. 1H NMR (500 MHz , CDCl3): δ=12.90 (s, 1H), 8.28 (d,
2H, J=9.2 Hz), 7.70 (d, 1H, J=7.6 Hz), 7.60 (s, 1H), 7.44 (d, 2H, J=9.1 Hz), 7.34-7.31
15

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(m, 1H), 7.18-7.15 (m, 1H), 6.94 (d, 1H, J=7.9 Hz). 13C NMR (125 MHz , DMSO-d6):
δ=162.76 (1C), 148.22 (1C), 141.51 (1C), 141.03 (1C), 131.73 (1C), 129.96 (1C),
125.63 (2C), 122.11 (1C), 120.47 (1C), 119.58 (1C), 113.86 (2C), 110.74 (1C). FTIR
(KBr, cm-1) 3298.9, 3226.2, 2433.7, 1694.3, 1603.6, 1568.1, 1506.9, 1463.2, 1329.6,
1254.0, 1206.6, 1160.4, 1108.6, 1018.0, 990.8, 888.3, 841.5, 789.3, 749.3, 688.7,
652.8, 585.8, 796.1, 448.0. HRMS (ESI): calcd for C14H11N4O3, [M + H]+ 283.0831,
found 283.0826.
4.2.4. 1-ethylindole-3-phenylhydrazone (compound 2d). Yellow solid. Yield 62%. Mp:
78-79 °C. 1H NMR (500 MHz, CDCl3) δ=12.83 (s, 1H), 7.68 (d, 1H, J=7.5 Hz ),
7.38-7.37 (m, 4H), 7.31- 7.29 (m, 1H), 7.14- 7.11 (m, 1H), 7.08- 7.05 (m, 1H), 6.93 (d,
1H, J=7.9 Hz ), 3.89 (q, 2H, J=7.3 Hz), 1.35 (t, 3H, J=7.3 Hz). . 13C NMR (125 MHz ,
CDCl3): δ=161.96 (1C), 142.77 (1C), 140.12 (1C), 129.41 (2C), 127.94 (1C), 127.17
(1C), 123.12 (1C), 122.40 (1C), 121.54 (1C), 119.04 (1C), 114.36 (2C), 108.49 (1C),
34.19 (1C), 13.07 (1C) . FTIR (KBr, cm-1) 3054.3, 1973.1, 2933.3, 1677.3, 1596.4,
1563.5, 1517.5, 1466.8, 1360.3, 1249.2, 1195.0, 1126.3, 1102.2, 1053.3, 994.1, 913.6,
784.4, 746.5, 691.0, 652.3, 545.8, 500.2, 426.8. HRMS (ESI): calcd for C16H16N3O,
[M + H]+ 266.1293, found 266.1288.
4.2.5. 1-ethylindole-3-(4-methoxyphenyl)hydrazone (compound 2e). Deep-yellow
solid. Yield 66%. Mp 110-111 °C. 1H NMR (500 MHz , CDCl3): δ=12.85 (s, 1H), 7.66
(d, 1H, J=7.6 Hz), 7.33-7.32 (m, 2H), 7.28-7.25 (m, 1H), 7.13 (t, 1H, J=7.7 Hz),
13
6.94-6.91 (m, 3H), 3.90 (q, 2H, J=7.3 Hz), 3.83 (s, 3H), 1.36 (t, 3H, J=7.3 Hz). C
NMR (125 MHz , CDCl3): δ=162.02 (1C), 156.18 (1C), 139.72 (1C), 136.63 (1C),
16

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127.45 (1C), 126.07 (1C), 122.27 (1C), 121.73 (1C), 118.70 (1C), 115.62 (2C),
114.91 (2C), 108.42 (1C), 55.66 (1C), 34.17 (1C), 13.12 (1C). FTIR (KBr, cm-1)
2971.1, 2934.0, 2838.4, 1673.7, 1610.6, 1562.0, 1518.9, 1466.7, 1363.8, 1296.1,
1233.9, 1125.3, 1100.0, 1038.0, 995.1, 914.0, 829.2, 783.0, 743.6, 708.2, 632.6, 538.1,
497.8, 454.2, 421.4. HRMS (ESI): calcd for C17H18N3O2, [M + H]+ 296.1399, found
296.1394.
4.2.6. 1-ethylindole-3-(4-nitrophenyl)hydrazone (compound 2f). Deep-yellow solid.
Yield 89%. Mp 247-249 °C. 1H NMR (500 MHz , CDCl3): δ=13.02 (s, 1H), 8.26 (d,
2H, J=9.3 Hz), 7.70 (d, 1H, J=7.2 Hz), 7.42-7.38 (m, 2H), 7.40-7.35 (m, 1H),
7.18-7.15 (m, 1H), 6.95 (d, 1H, J=7.9 Hz), 3.87 (q, 2H, J=7.2 Hz), 1.36 (t, 3H, J=7.3
Hz). 13C NMR (125 MHz , DMSO-d6): δ=163.13 (1C), 149.71 (1C), 142.70 (1C),
141.53 (1C), 132.90 (1C), 131.28 (1C), 124.84 (2C), 121.65 (1C), 119.43 (1C),
115.18 (1C), 114.48 (2C), 108.90 (1C), 33.93 (1C), 12.57 (1C). FTIR (KBr, cm-1)
3545.3, 3441.0, 3250.2, 2981.4, 2942.9, 1679.2, 1599.4, 1572.3, 1499.8, 1465.3,
1378.9, 1332.3, 1264.8, 1210.5, 1164.2, 1107.3, 1052.3, 914.9, 846.4, 781.1, 754.3,
693.1, 553.1, 497.0. HRMS (ESI): calcd for C16H15N4O3, [M + H]+ 311.1144, found
311.1139.
4.2.7. 1-benzylindole-3-phenylhydrazone (compound 2g). Yellow solid. Yield 83%.
1
Mp: 138-139 °C. H NMR (500 MHz , CDCl3): δ=12.84 (s, 1H) 7.69 (d, 1H, J=7.3
Hz ) 7.68-7.37 (m, 4H), 7.36-7.30 (m, 4H), 7.30-7.28 (m, 1H), 7.22-7.13 (m, 1H),
7.13-7.07 (m, 2H), 6.82 (d, 1H, J=7.9 Hz), 5.02 (s, 2H). 13C NMR (125 MHz , CDCl3):
δ=162.27 (2C), 142.63 (1C), 140.18 (1C), 135.83 (1C), 129.46 (2C), 128.88 (2C),
17

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127.96 (1C), 127.75 (1C), 127.29 (2C), 126.76 (1C), 123.29 (1C), 122.67 (1C),
121.46 (1C), 118.95 (1C), 114.42 (1C), 109.35 (1C), 43.24 (1C). FTIR (KBr, cm-1)
3056.7, 3031.0, 1663.8, 1596.7, 1556.8, 1515.2, 1466.3, 1360.9, 1299.9, 1246.8,
1167.8, 1105.0, 1078.4, 1036.9, 1007.5, 785.2, 745.2, 695.1, 665.5, 627.1, 546.7,
454.6. HRMS (ESI): calcd for C21H18N3O, [M + H]+ 328.1450, found 328.1444.
4.2.8. 1-p-tert-butylbenzylindole-3-phenylhydrazone (compound 2h). Yellow solid.
Yield 80%. Mp 126-128 °C. 1H NMR (500 MHz , CDCl3): δ=12.84 (s, 1H), 7.68 (d,
1H, J=7.5 Hz), 7.41-7.35 (m, 6H), 7.28 (s, 1H), 7.27 (s, 1H), 7.25-7.20 (m, 1H),
7.13-7.11 (m, 1H), 7.09-7.06 (m, 1H), 6.87 (d, 1H, J=7.9 Hz), 4.99 (s, 2H), 1.30 (s,
9H). 13C NMR (125 MHz , CDCl3): δ=162.29 (1C), 150.76 (1C), 142.73 (1C), 140.39
(1C), 132.84 (1C), 129.44 (2C), 127.95 (1C), 127.11 (2C), 126.93 (1C), 125.78 (2C),
123.25 (1C), 122.59 (1C), 121.52 (1C), 118.94 (1C), 114.44 (2C), 109.37 (1C), 42.95
(1C), 34.53 (1C), 31.32 (3C). FTIR (KBr, cm-1) 3055.7, 2960.5, 1667.4, 1596.0,
1562.7, 1508.8, 1466.6, 1353.9, 1243.4, 1164.1, 1102.2, 1034.1, 1007.8, 887.1, 784.1,
747.7, 692.1, 652.5, 547.4, 451.3. HRMS (ESI): calcd for C25H26N3O, [M + H]+
384.2076, found 384.2070.
4.2.9. 1-p-tert-butylbenzylindole-3-(4-methoxyphenyl)phenylhydrazone (compound 2i).
Deep-yellow solid. Yield 82%. Mp 151-152 °C. 1H NMR (500 MHz , CDCl3): δ=
12.87 (s, 1H), 7.66 (d, 1H, J=7.3 Hz), 7.80 (dd, 3H, J1=3.25 Hz, J2= 3.30 Hz), 7.21 (t,
1H, J=7.5 Hz), 7.11 (t, 1H, J=7.3 Hz), 6.95 (d, 2H, J=1.95 Hz), 6.87 (d, 1H, J=7.8
Hz), 4.99 (s, 2H), 3.88 (s, 2H), 3.84 (s, 3H), 1.30 (s, 9H). 13C NMR (125 MHz ,
CDCl3): δ=162.31 (1C), 156.25 (1C), 150.69 (1C), 139.98 (1C), 136.56 (1C), 132.98
18

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(1C), 127.44 (1C), 127.09 (2C), 125.75 (2C), 122.45 (2C), 121.69 (1C), 118.58 (1C),
115.74 (1C), 115.69 (2C), 114.92 (2C), 109.27 (1C), 55.66 (1C), 42.90 (1C), 34.53
(1C), 31.32 (3C). FTIR (KBr, cm-1) 3055.0, 2959.8, 2866.1, 2843.2, 1665.3, 1610.8,
1552.4, 1517.2, 1466.1, 1358.8, 1300.6, 1239.7, 1164.4, 1101.9, 1039.6, 1008.4,
820.8, 783.8, 743.0, 713.3, 657.1, 607.2, 532.6, 451.5. HRMS (ESI): calcd for
C26H27N3O2, [M + H]+ 414.2182, found 414.2176.
4.2.10. 1-p-tert-butylbenzylindole-3-(4-nitrophenyl)phenylhydrazone (compound 2j).
Deep-yellow solid. Yield 95%. Mp 198-201 °C. 1H NMR (500 MHz , CDCl3): δ=
13.03 (s, 1H), 8.28-8.26 (m, 3H), 7.70-7.69 (m, 1H), 7.43-7.42 (m, 2H), 7.38-7.36 (m,
3H), 7.29-7.26 (m, 1H), 7.16-7.13 (m, 1H), 6.90-6.88 (m, 1H), 4.97 (s, 2H), 1.30 (s,
9H). 13C NMR (125 MHz , CDCl3): δ=162.20 (1C), 151.08 (1C), 147.90 (1C), 142.72
(1C), 141.54 (1C), 132.29 (1C), 130.93 (1C), 129.72 (2C), 127.15 (2C), 125.92 (2C),
125.89 (1C), 123.15 (1C), 120.55 (1C), 119.98 (1C), 114.28 (1C), 113.65 (2C),
109.84 (1C), 43.15 (1C), 34.57 (1C), 31.31 (3C). FTIR (KBr, cm-1) 2962.4, 2865.7,
1734.6, 1681.1, 1603.1, 1570.2, 1505.9, 1465.8, 1331.2, 1258.1, 1151.5, 1101.6,
1032.6, 1004.6, 970.8, 845.2, 787.7, 751.5, 694.6, 630.2, 495.0. HRMS (ESI): calcd
for C25H25N4O3, [M + H]+ 429.1927, found 429.1921.
4.3 Preparation of compounds 3a-3j
To a stirred solution of 2d (0.1328 g, 0.5 mmol) in degassed anhydrous
dichloromethane (20 mL), Et3N (1.5 mL, 10 mmol) was syringed under nitrogen
atmosphere. After stirred for 20 minutes, BF3·OEt2 (1.25 mL, 10 mmol) was
19

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successively added by syring. The mixture was stirred at room temperature overnight
and complete reaction was detected by TLC. The mixture was quenched with water
(20 mL), and extracted with dichloromethane (3 * 20 mL). The organic layer was
dried with MgSO4 and the solvent was removed under reduced pressure. The residue
was purified by silica gel chromatography eluting (silica gel, ethyl acetate: petroleum
ether = 1: 10) to afford clean complex 3d as an orange-yellow solid.
4.3.1. 5-H-3,3-difluoro-2-phenyl-3,5-dihydro-2H-[1,3,4,2]oxadiazaborinino[6,5-b]in-
dol-4-ium-3-uide (compound 3a). Orange solid. Yield 64 %. Mp 197-202 °C. 1H NMR
(500 MHz , DMSO-d6): δ=13.50 (s, 1H), 7.82 (d, 1H, J=7.6 Hz), 7.69 (d, 2H, J=8.0
Hz), 7.50-7.47 (m, 2H), 7.42-7.36 (m, 2H), 7.35-7.29 (m, 2H). 19F NMR (CDCl3, 376
MHz): δ=-130.42- -130.45 (m, 1F), -131.48- -130.51 (m, 1F). FTIR (KBr, cm-1)
3376.2, 3359.5, 3066.1, 1639.4, 1592.0, 1492.3, 1458.6, 1321.2, 1297.5, 1254.3,
1194.5, 1110.8, 1043.8, 1019.6, 969.6, 894.1, 757.2, 689.3, 630.8, 574.8, 439.7.
HRMS (ESI): calcd for C14H10BF2N3O Na, [M + Na]+ 308.0783; found 308.0785.
4.3.2. 5-H-3,3-difluoro-2-(4-methoxyphenyl)-3,5-dihydro-2H-[1,3,4,2]oxadiazaborin-
ino[6,5-b]indol-4-ium-3-uide (compound 3b). Red solid. Yield 92%. Mp 183-185 °C.
1H NMR (500 MHz , DMSO-d6): δ=13.36 (s, 1H), 7.80 (d, 1H, J=7.5 Hz), 7.63 (d, 1H,
J=8.8 Hz), 7.41-7.36 (m, 2H), 7.33-7.30 (m, 1H), 7.06-7.05 (m, 2H), 3.81 (s, 3H). 19F
NMR (CDCl3, 376 MHz): δ=-130.05- -130.08 (m, 1F), -131.12- -130.15 (m, 1F).
FTIR (KBr, cm-1) 3264.9, 3207.1, 1635.8, 1592.9, 1500.2, 11427.8, 1322.5, 1240.7,
1181.1, 1046.4, 1021.6, 973.9, 887.1, 827.3, 763.7, 557.3. HRMS (ESI): calcd for
20

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C15H11BF2N3O2, [M - H]+ 314.0912; found 314.0912.
4.3.3. 5-H-3,3-difluoro-2-(4-nitrophenyl)-3,5-dihydro-2H-[1,3,4,2]oxadiazaborin-
ino[6,5-b]indol-4-ium-3-uide (compound 3c). Orange solid. Yield 78%. Mp
1
183-185 °C. H NMR (500 MHz , DMSO-d6): δ=8.35-8.32 (m, 2H), 7.90-7.85 (m,
3H), 7.47-7.44 (m, 1H), 7.38-7.34 (m, 2H). 19F NMR (CDCl3, 376 MHz): δ=-129.38-
-129.40 (m, 1F), -131.46- -130.48 (m, 1F). FTIR (KBr, cm-1) 3359.4, 1660.4, 1594.9,
1544.7, 1490.7, 1459.9, 1423.2, 1332.6, 1259.3, 1172.4, 1110.8, 1074.2, 1022.1,
964.2, 852.4, 775.3, 752.1, 661.5, 441.6. HRMS (ESI): calcd for C14H8BF2N4O3, [M -
H]+ 329.0658; found 329.0658.
4.3.4. 5-ethyl-3,3-difluoro-2-phenyl-3,5-dihydro-2H-[1,3,4,2]oxadiazaborinino[6,5-b]
1
indol-4-ium-3-uide (compound 3d). Orange solid. Yield 80%. Mp 163-166 °C . H
NMR (500 MHz, CDCl3): δ=7.90-7.88 (m, 1H), 7.85-7.83 (m, 2H), 7.47-7.44 (m, 2H),
7.40-7.39 (m, 2H), 7.39-7.36 (m, 1H), 7.35-7.26 (m, 1H), 4.19 (q, 2H, J=7.4 Hz), 1.53
(t, 3H, J=7.4 Hz). 13C NMR (125 MHz , CDCl3): δ=152.84 (1C), 145.16 (1C), 136.02
(1C), 128.94 (2C), 126.85 (1C), 126.54 (1C), 124.88 (1C), 123.29 (1C), 121.56 (1C),
120.72 (1C), 119.01 (2C), 110.74 (1C), 36.72 (1C), 13.45 (1C). 19F NMR (CDCl3, 376
MHz): δ=-130.94 (s, 1F), -131.00 (s, 1F). FTIR (KBr, cm-1) 2987.2, 1608.4, 1508.5,
1321.0, 1282.5, 1210.1, 1135.9, 1023.3, 761.8, 545.8, 432.0. HRMS (ESI): calcd for
C16H15BF2N3O, [M + H]+ 314.1271, found 314.1273.
4.3.5. 5-ethyl-3,3-difluoro-2-(4-methoxyphenyl)-3,5-dihydro-2H-[1,3,4,2]oxadiazab-
orinino[6,5-b]indol-4-ium-3-uide (compound 3e). Red solid. Yield 80%. Mp
21

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1
163-165 °C. H NMR (500 MHz , CDCl3): δ=7.87 (dd, 1H, J1=1.4 Hz, J2 =1.4 Hz),
7.80 (d, 2H, J=9.0 Hz), 7.37-7.34 (m, 2H), 7.28-7.25 (m, 1H), 6.97 (d, 2H, J=3.3 Hz),
4.17(q, 2H, J=7.3 Hz), 3.87 (s, 3H), 1.50 (t, 3H, J=7.3 Hz); 13CNMR (125 MHz ,
CDCl3): δ=158.84 (1C),152.33 (1C), 138.86 (1C), 135.63 (1C), 126.06 (1C), 124.63
(1C), 122.17 (1C), 121.65 (1C), 118.74 (1C), 115.56 (1C), 114.84 (1C), 114.22 (2C),
19
110.61 (1C), 55.57 (1C), 36.65 (1C), 13.53 (1C). F NMR (CDCl3, 376 MHz):
δ=-131.66- -131.68 (m, 1F), -131.72- -131.74 (m, 1F). FTIR (KBr, cm-1) 1631.5,
1500.4, 1427.6, 1322.8, 1250.4, 1212.3, 1137.5, 1023.5, 827.3, 543.8. HRMS (ESI):
calcd for C17H17BF2N3O2, [M + H]+ 344.1376, found 344.1378.
4.3.6. 5-ethyl-3,3-difluoro-2-(4-nitrophenyl)-3,5-dihydro-2H-[1,3,4,2]oxadiazaborini-
no[6,5-b]indol-4-ium-3-uide (compound 3f). Orange solid. Yield 85%. Mp
1
211-215 °C. H NMR (500 MHz , CDCl3): δ=8.30-8.27 (m, 2H), 7.97 (d, 2H, J=9.2
Hz), 7.91 (d, 1H, J=7.4 Hz), 7.49-7.46 (m, 1H), 7.43-7.40 (m, 1H), 7.30-7.28 (m, 1H),
4.19 (q, 2H, J=7.3 Hz), 1.54 (t, 3H, J=7.4 Hz); 13C NMR (125 MHz, CDCl3)
δ=153.93 (1C), 150.12 (1C), 145.22 (1C), 137.21 (1C), 128.09 (1C), 125.77 (1C),
124.76 (2C), 121.91 (1C), 121.08 (1C), 120.01 ((1C), 119.99 (2C), 111.26 (1C), 37.13
(1C), 13.29 (1C). 19F NMR (CDCl3, 376 MHz): δ=-130.15- -130.17 (m, 1F), -130.22-
-130.25 (m, 1F). FTIR (KBr, cm-1) 1639.2, 1594.9, 1505.6, 1491.3, 1423.2, 1341.9,
1277.3, 1203.3, 1135.3, 1110.4, 1024.0, 972.0, 852.4, 773.3, 752.1, 653.8. HRMS
(ESI): calcd for C16H13BF2N4O3 Na, [M + Na]+ 381.0946, found 381.0946.
4.3.7. 5-benzyl-3,3-difluoro-2-phenyl-3,5-dihydro-2H-[1,3,4,2]oxadiazaborinino[6,5-
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1
b]indol-4-ium-3-uide (compound 3g). Orange solid. Yield 84%. Mp: 145-149 °C. H
NMR (500 MHz , CDCl3): δ=7.89-7.86 (m, 3H), 7.48 (t, 2H, J=1.9 Hz), 7.45-7.28 (m,
13
8H), 7.17 (d, 1H, J=7.4 Hz), 5.27 (s, 2H). C NMR (125 MHz , CDCl3): δ=153.14
(1C), 145.20 (1C), 136.28 (1C), 133.48 (1C), 129.30 (2C), 128.92 (2C), 128.72 (1C),
127.67 (2C), 127.11 (1C), 126.59 (1C), 125.03 (1C), 123.13 (1C), 121.58 (1C),
19
120.90 (1C), 118.95 (1C), 114.46 (1C), 111.62 (1C), 45.52 (1C). F NMR (CDCl3,
376 MHz): δ=-130.96 (s, 1F), -131.02 (s, 1F). FTIR (KBr, cm-1) 3060.5, 1634.0,
1508.1, 1458.1, 1266.7, 1183.4, 1133.0, 1023.8, 881.3, 757.9, 555.4. HRMS (ESI):
calcd for C21H17BF2N3O, [M + H]+ 376.1427, found 376.1436.
4.3.8. 5- p-tert-butylbenzylindole -3,3-difluoro-2-phenyl-3,5-dihydro-2H-[1,3,4,2]oxa-
diazaborinino[6,5-b]indol-4-ium-3-uide (compound 3h). Orange solid. Yield 83%.
1
Mp: 152-153 °C. H NMR (500 MHz , CDCl3): δ=7.88-7.85 (m, 3H), 7.48-7.45 (m,
2H), 7.41-7.39 (m, 2H), 7.34-7.28 (m, 5H), 7.23-7.21 (m, 1H), 5.25 (s, 2H), 1.30 (s,
9H); 13CNMR (125 MHz , CDCl3): δ=153.07 (1C), 151.81 (1C), 145.19 (1C), 136.34
(1C), 130.42 (2C), 128.98 (2C), 127.48 (2C), 127.10 (1C), 127.00 (1C), 126.52 (2C),
124.93 (1C), 123.16 (1C), 121.57 (1C), 120.84 (1C), 118.88 (1C), 114.40 (1C), 111.61
(1C), 45.16 (1C), 34.63 (1C), 31.31 (3C). 19F NMR (CDCl3, 376 MHz): δ=-131.07 (s,
1F), -131.11 (s, 1F). FTIR (KBr, cm-1) 2962.2, 1606.4, 1508.4, 1461.8, 1321.0, 1027.1,
887.1, 815.8, 763.7, 690.4, 557.3. HRMS (ESI): calcd for C25H25BF2N3O, [M + H]+
432.2053, found 432.2061.
4.3.9. 5- p-tert-butylbenzylindole -3,3-difluoro-2-(4-methoxyphenyl)-3,5-dihydro-2H-
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[1,3,4,2]oxadiazaborinino[6,5-b]indol-4-ium-3-uide (compound 3i). Red solid. Yield
1
78%. Mp:156-157 °C. H NMR (500 MHz , CDCl3): δ=7.87-7.85 (m, 1H), 7.80 (d,
2H, J=9.0 Hz), 7.40- 7.38 (m, 2H), 7.34-7.28 (m, 4H), 7.22-7.20 (m, 1H), 6.99 (d, 2H,
13
J=2.0 Hz), 5.24 (s, 2H), 3.88 (s, 3H), 1.30 (s, 9H); CNMR (125 MHz , CDCl3): δ=
158.94 (1C), 152.52 (1C), 151.70 (1C), 138.86 (1C), 135.94 (1C), 130.61 (1C),
127.41 (2C), 126.10 (2C), 124.69 (2C), 122.25 (2C), 121.59 (1C), 118.58 (1C),
114.23 (2C), 111.49 (2C), 55.57 (1C), 45.06 (1C), 34.60 (1C), 31.22 (3C). 19F NMR
(CDCl3, 376 MHz): δ=-131.61 (s, 1F), -131.67 (s, 1F). FTIR (KBr, cm-1) 2941.0,
2738.5, 2678.7, 2491.6, 1606.4, 1499.9, 1427.1, 1323.9, 1248.8, 1176.3, 1026.1,
883.3, 833.1, 545.8. HRMS (ESI): calcd for C26H27BF2N3O2, [M + H]+ 462.2159,
found 462.2160.
4.3.10. 5- p-tert-butylbenzylindole -3,3-difluoro-2-(4-nitrophenyl)-3,5-dihydro-2H-[1,
3,4,2]oxadiazaborinino[6,5-b]indol-4-ium-3-uide (compound 3j). Orange solid. Yield
70%. Mp: 220-222 °C. 1H NMR (500 MHz, CDCl3) δ=8.31-8.29 (m, 2H), 7.99 (d, 2H,
J=9.0 Hz), 7.91-7.89 (m, 1H), 7.42-7.38 (m, 4H), 7.31 (d, 2H, J=8.3 Hz), 7.27-7.24
(m, 1H), 5.25 (s, 2H), 1.31 (s, 9H); 13C NMR (125 MHz, CDCl3) δ=154.12 (1C),
152.30 (1C), 145.32 (1C), 137.53 (1C), 129.74 (1C), 128.09 (1C), 127.58 (2C),
126.36 (2C), 125.76 (1C), 124.78 (2C), 124.43 (1C), 121.05 (1C), 120.13 (1C),
120.12 (1C), 119.81 (1C), 115.60 (1C), 112.15 (1C), 45.56 (1C), 34.68 (1C), 31.24
(3C). 19F NMR (CDCl3, 376 MHz): δ=-130.08 (s, 1F), -131.12 (s, 1F). FTIR (KBr,
cm-1) 2964.1, 1594.9, 1544.7, 1504.2, 1490.4, 1423.2, 1306.2, 1262.7, 1169.0, 1154.7,
1108.3, 1029.8, 850.5, 752.1, 673.0, 437.8. HRMS (ESI): calcd for C25H23N4O3, [M -
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BF2]+ 427.1770, found 427.1724.
Acknowledgement
We gratefully acknowledge the financial supported by the Natural Science
Foundation of China (21176223) and the National Natural Science Foundation of
Zhejiang (LY13B020016) and the Key Innovation Team of Science and Technology
in Zhejiang Province (2010R50018).
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