Synthesis and characterization of oxadisilole-fused 1H-benzo[f]indazoles and 1H-naphtho[2,3-f]indazoles

Article abstract of DOI:10.1002/ejoc.201300110

Oxadisilole-fused 1H-benzo[f]- and 1H-naphtho[2,3-f]indazoles have been synthesized by the 1,3-dipolar cycloaddition reactions of benzo- or naphtho-oxabicycloalkenes with nitrile imines generated in situ from N-arylhydrazonoyl chlorides followed by deoxygenation and aromatization. The photophysical, redox and thermal properties of these compounds have been characterized. Some of the indazoles show potential as deep-blue emitters for OLED applications as a result of their high fluorescence quantum yields and good thermal stabilities. Oxadisilole-fused 1H-benzo[f]- and 1H-naphtho[2,3-f] indazoles have been synthesized by the 1,3-dipolar cycloaddition of benzo- or naphtho-oxabicycloalkenes with nitrile imines followed by deoxygenation and aromatization. Their photophysical, redox and thermal properties show that some of the indazoles show potential as deep-blue emitters for OLED applications. Copyright

Full text of DOI:10.1002/ejoc.201300110

FULL PAPER
DOI: 10.1002/ejoc.201300110
Synthesis and Characterization of Oxadisilole-Fused 1H-Benzo[f]indazoles and
1H-Naphtho[2,3-f]indazoles
Yajuan Zhang,[a][‡] Xuyan Ma,[a][‡] Yali Chen,*[a] Xuanming Chen,[a] Lei Guo,[b]
Weiguo Cao,[a] Jie Chen,[a] and Man Shing Wong*[b]
Keywords: Fused-ring systems / Heterocycles / Cycloaddition / Fluorescence / Cyclic voltammetry
Oxadisilole-fused 1H-benzo[f]- and 1H-naphtho[2,3-f]-
indazoles have been synthesized by the 1,3-dipolar cycload-
dition reactions of benzo- or naphtho-oxabicycloalkenes with
nitrile imines generated in situ from N-arylhydrazonoyl
chlorides followed by deoxygenation and aromatization. The
photophysical, redox and thermal properties of these com-
pounds have been characterized. Some of the indazoles show
potential as deep-blue emitters for OLED applications as a
result of their high fluorescence quantum yields and good
thermal stabilities.
Recently, we became interested in the chemistry of arynes
generated from benzobis(oxadisilole), benzotris(oxadisilole)
and 2,3-naphthoxadisilole under very mild conditions. We
reported the synthesis of oxadisilole-fused benzo[d]isoxaz-
oline, benzotriazole and benzisoxazole derivatives as well as
the naphtho[2,3-d]isoxazoline, naphthotriazole and naph-
thisoxazole derivatives by the 1,3-dipolar cycloaddition of
nitrones, azides and nitrile oxides to arynes generated from
benzobis(oxadisilole) and 2,3-naphthoxadisilole, respec-
tively, under very mild conditions.[13] On the other hand,
our attempt to synthesize 6a by the 1,3-dipolar cycload-
dition reaction of oxadisilole-fused benzyne 3 with nitrile
imine 5a was in vain (Scheme 1), likely because of the prob-
lem of simultaneous in situ generation of reactive nitrile
imine 5a from N-arylhydrazonoyl chloride 4a and benzyne
3 moieties derived from benzobis(oxadisilole) 1. In this con-
tribution we report our findings on the synthesis of oxa-
disilole-fused 1H-benzo[f]indazoles 9a–e and 1H-naphtho-
[2,3-f]indazoles 15a–e by 1,3-dipolar cycloaddition reac-
tions of oxabicyclic alkenes 7 and 13, respectively, with ni-
Introduction
1,3-Dipolar cycloaddition reactions have received con-
siderable attention because they have been shown to be an
efficient synthetic tool for the preparation of a wide variety
of heterocyclic compounds.[1] Nitrile imines are versatile
1,3-dipoles that undergo cycloaddition reactions with a
wide range of alkenes,[2] alkynes,[3] C=N[4] and C=S com-
pounds[5] and benzyne,[6] allowing the construction of sub-
stituted pyrazole, indazole and other azo heterocycles. Pyr-
azoles[7] and indazoles[8] exhibit diverse bioactivities and
pharmacological activities, including anti-HIV, Rho-kinase
inhibition, anti-fertility, anti-arthritic, anti-inflammatory,
and contraceptive activities. Meanwhile, the use of pyrazole
derivatives such as dipyrazolopyridines or pyrazoloquinol-
ines as efficient blue or green light-emitting materials in
multi-layer OLEDs has been reported.[9] Various methods
for the synthesis of the 1H-indazole (benzopyrazole) core
have been developed.[10] Recently, several methodologies
have been reported that involve aryne intermediates in [3+2]
cycloaddition reactions with diazo compounds[6b,11] and in
situ generated nitrile imines.[6] Most benzynes are com-
monly accessed in situ by fluoride-promoted ortho elimi-
nation of o-(trimethylsilyl)aryl triflates.[6,11] The formation
of the benzyne of benzoxadisilole by phenyliodination with
o-bis(trimethylsilyl)benzene has also been reported by Kita-
mura and Yamane.[12]
[a] Department of Chemistry, Shanghai University,
Shanghai 200444, P. R. China
Fax: +86-21-66132797
E-mail: ylchen@staff.shu.edu.cn
[b] Department of Chemistry, Hong Kong Baptist University,
Kowloon Tong, Hong Kong, China
[‡] These authors contributed equally to this work
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201300110.
Scheme 1. Synthesis of oxadisilole-fused 1H-indazole 6a proved not
to be feasible.
Eur. J. Org. Chem. 2013, 3005–3012
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Y. Chen, M. S. Wong et al.
FULL PAPER
trile imines 5a–e followed by deoxygenation and aromatiza-
tion. The oxabicyclic alkenes 7 and 13 are the furan cy-
cloadducts of benzyne 3 and naphthyne 12 generated from
Results and Discussion
The procedures for the synthesis of the oxadisilole-fused
1H-benzo[f]indazoles 9a–e or 1H-naphtho[2,3-f]indazoles
15a–d are outlined in Schemes 2 and 3. The oxabicyclic alk-
enes 7 and 13 were prepared according to our previously
reported phenyliodination/fluoride-induced desilylation
protocol by trapping the arynes (3 and 12) generated from
1 and 10 with furan in yields of 88 and 54%, respectively.[14]
The 1,3-dipolar nitrile imines 5a–e are reactive intermedi-
ates, commonly generated in situ by the base-induced de-
hydrodechlorination of N-arylhydrazonoyl chlorides 4a–
e.[6,11] Compounds 4a–e were prepared according to litera-
ture procedures.[6] Oxadisilole-fused benzo-oxabicyclic
alkene 7 and naphtho-oxabicyclic alkene 13 reacted with
nitrile imines 5a–e by 1,3-dipolar cycloaddition to afford
8a–e and 14a–e, respectively, in good yields. After deoxy-
genation followed by aromatization, oxadisilole-fused 1H-
benzo[f]indazoles 9a–e and 1H-naphtho[2,3-f]indazoles
15a–d, respectively, were synthesized.
benzobis(oxadisilole)
1 and 2,3-naphthoxadisilole 10,
respectively (see Schemes 2 and 3).[14] The nitrile imine di-
poles 5a–e were generated by treating N-arylhydrazonoyl
chlorides 4a–e with base.[6] The deoxygenation protocol de-
picted in Schemes 2 and 3 leads to the linear polycyclic aro-
matic skeletons. The previously unknown compounds 9a–e
and 15a–d were characterized.
We optimized the procedure by starting with the reaction
of oxadisilole-fused benzo-oxabicyclic alkene 7 and nitrile
imine 5d generated in situ from the corresponding 4d
(1.2 equiv.) with triethylamine as base at room temperature
in CHCl3 for 24 h. The [3+2] cycloadduct 8d was obtained
in 46% isolated yield (Scheme 2, Table 1, entry 1). By using
2.0 and 3.0 equiv. of 4d at room temperature for 24 h, 8d
was obtained in yields of 48 and 56%, respectively (Table 1,
entries 2 and 3). The [3+2] cycloaddition reaction of 7 with
5d, obtained from 3.0 and 2.0 equiv. of 4d, at 50 °C for 24 h
improved the yield of product 8d to 67 and 68%, respec-
tively (Table 1, entries 4 and 5). Shortening the reaction
time to 6 h at 50 and 60 °C also gave higher yields of 74
and 71%, respectively (Table 1, entries 6 and 7). Thus, the
optimal results were obtained when the reaction between 7
and 5d was performed with 2.0 equiv. of 4d in CHCl3 at
50 °C for 6 h (Table 1, entry 6).
Scheme 2. Synthesis of oxadisilole-fused 1H-benzo[f]indazoles
9a–e.
Table 1. Optimization of the conditions for the reaction between 7
(1 equiv.) and 5d generated from 4d in CHCl3.
Entry 4d [equiv.]
T [°C]
Time [h]
Yield[a] [%]
1
2
3
4
5
6
7
1.2
2.0
3.0
3.0
2.0
2.0
2.0
r.t.
r.t.
r.t.
50
50
50
60
24
24
24
24
24
6
46
48
56
67
68
74
71
6
[a] Isolated yield.
We then studied the 1,3-dipolar cycloaddition reaction
of oxadisilole-fused benzo-oxabicyclic alkene 7 with various
nitrile imine dipoles 5a–e generated in situ from the corre-
sponding hydrazonoyl chlorides 4a–e in CHCl3 at 50 °C for
6 h. The cycloadducts 8a–e were obtained in yields of 58–
89% (Scheme 2, Table 2, entries 1–5). The results indicate
that the cycloaddition reactions of 7 with 5a–e are quite
sensitive to the electronic nature (X = OCH3, CH3, H, Cl,
NO2) of the substituents on the phenyl rings of 4a–e; the
Scheme 3. Synthesis of 1H-naphtho[2,3-f]indazoles 15a–d.
3006
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Eur. J. Org. Chem. 2013, 3005–3012

Oxadisilole-Fused 1H-Benzo[f]- and 1H-Naphtho[2,3-f]indazoles
electron-rich hydrazonoyl chlorides gave higher yields than desired product 9d was obtained in yields of 56, 57 and
the electron-deficient compounds. Thus, the stronger the 63%, respectively (Table 3, entries 5–7). Thus, the optimal
electron-donating nature of the substituent (X = OCH3; conditions were the use TiCl4/LiAlH4/Et3N in CH2Cl2 at
Table 2, entry 1), the higher the isolated yield. In contrast, room temperature with a reaction time of 24 h (Table 3, en-
the stronger the electron-withdrawing nature of the substit- try 4).
uent (X = NO2), the poorer the yield (Table 2, entry 5).
Having established the optimal reaction conditions, we
studied the deoxygenation of 8a–e with TiCl4/LiAlH4/Et3N
in CH2Cl2 at room temperature for 24 h; oxadisilole-fused
1H-benzo[f]indazoles 9a–e were obtained in yields of 18–
67% (Scheme 2, Table 4, entries 1–5). Note that the yield of
9e (X = NO2) was rather poor (Table 4, entry 5).
Table 2. Cycloaddition reactions of 7 and 13 (1 equiv.) with 5a–e
generated from 4a–e (2 equiv.) in CHCl3 at 50 °C.
Entry
Hydrazonoyl
chloride
X
Oxabicyclic Product Yield[a]
alkene
[%]
1
2
3
4
5
6
7
8
9
10
4a
4b
4c
4d
4e
4a
4b
4c
4d
4e
OCH3
CH3
H
7
7
8a
8b
89
78
76
74
58
78
89
84
67
49
Table 4. Synthesis of 9a–e and 15a–d by the deoxygenation of 8a–e
and 14a–e in the presence of TiCl4, Et3N and LiAlH4 in CH2Cl2.[a]
7
8c
Cl
7
7
13
13
13
13
13
8d
8e
14a
14b
14c
14d
14e
Entry
Cycloadduct
X
Product
Yield[b] [%]
NO2
OCH3
CH3
H
Cl
NO2
1
2
3
4
5
6
7
8
9
8a
8b
OCH3
CH3
H
9a
9b
60
63
47
67
18
43
69
65
62
8c
9c
8d
8e
14a
14b
14c
14d
Cl
9d
9e
15a
15b
15c
15d
NO2
OCH3
CH3
H
[a] Isolated yield.
We then turned out attention to the 1,3-dipolar cycload-
dition reaction of naphtho-oxabicyclic alkene 13 with vari-
ous nitrile imine dipoles 5a–e generated in situ from the
corresponding hydrazonoyl chlorides 4a–e in CHCl3 at
50 °C for 6 h. Both the electron-rich and -deficient dipoles
successfully participated in the [3+2] cycloaddition reaction
to afford the desired products 14a–e in yields of 49–89%
(Scheme 3, Table 2, entries 6–10). Again, a strongly elec-
tron-withdrawing substituent (X = NO2) on the phenyl ring
led to a lower yield (Table 2, entry 10).
As outlined in Scheme 2 and Scheme 3, deoxygenation of
the cycloadducts 8a–e and 14a–e with TiCl4/LiAlH4/Et3N
in CH2Cl2 afforded the oxadisilole-fused 1H-benzo[f]-
indazoles 9a–e and 1H-naphtho[2,3-f]indazoles 15a–d,
respectively, under mild conditions.
Cl
[a] The reactions of 8a–e were performed at room temp. for 24 h
and the reactions of 14a–e were performed at 40 °C for 1 h. [b]
Isolated yield.
Aromatization by the deoxygenation of 14b with TiCl4/
LiAlH4/Et3N in CH2Cl2 at room temperature for 24 h af-
forded 1H-naphtho[2,3-f]indazole 15b in only 6% yield
(Scheme 3, Table 5, entry 1). The reaction was optimized
and the results are summarized in Table 5. It was found that
the deoxygenation of 14b at 40 °C for 1 h greatly improved
the yield of 15b to 69% (Table 5, entry 5).
Table 5. Optimization of the synthesis of 15d by the deoxygenation
of 14d in the presence of TiCl4, Et3N and LiAlH4 in CH2Cl2.
Entry
T [°C]
Time [h]
Yield[a] [%]
The deoxygenation/aromatization[14] of cycloadduct 8d
with TiCl4/LiAlH4/Et3N in THF at room temperature for
24 h afforded the oxadisilole-fused 1H-benzo[f]indazole 9d
in 6% yield (Table 3, entry 1). To tackle the low yield, the
reaction conditions were optimized. No product was de-
tected with DME as the solvent (Table 3, entry 2). By
changing the solvent to toluene or CH2Cl2, the product
yield greatly improved to 32 and 67%, respectively (Table 3,
entries 3 and 4). When the reaction was performed for 12
or 30 h and the temperature was increased to 40 °C, the
1
2
3
4
5
6
r.t.
40
40
40
40
40
24
24
5
3
1
6
14
17
26
69
53
0.5
[a] Isolated yield.
The same reaction sequence was then applied to the de-
oxygenation of 14a–e under the optimized conditions of
TiCl4/LiAlH4/Et3N in CH2Cl2 at 40 °C for 1 h. 1H-
Naphtho[2,3-f]indazoles 15a–d were obtained in yields of
43–69% (Scheme 3, Table 4, entries 6–9). Again, the desired
product 15e, bearing the strongly electron-withdrawing
group NO2, could not be obtained.
The structues of compounds 8a–e, 9a–e, 14a–e and 15a–
d were established by 1H and 13C NMR and IR spec-
troscopy, MS and elemental analysis; the results were in
good agreement with the expected structures.
Table 3. Optimization of the synthesis of 9d by the deoxygenation
of 8d in the presence of TiCl4, Et3N and LiAlH4.
Entry Solvent
T [°C]
Time [h]
Yield[a] [%]
1
2
3
4
5
6
7
THF
DME
toluene
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
40
24
24
24
24
12
30
24
6
0
32
67
56
57
63
The absorption spectra of 9a–e and 15a–d were recorded
in CH2Cl2 and the spectral data are summarized in Table 6.
The absorption spectra of 9a–e and 15a–d show the charac-
[a] Isolated yield.
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Y. Chen, M. S. Wong et al.
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teristic strong β-band absorption at approximately 268 nm
for 9a–e and 277 nm for 15a–d, with the long wavelength
absorption bands located between 386 and 400 nm for 9a–
e and 484 and 487 nm for 15a–d (Figures 1 and 2). A slight
redshift is observed for the absorption maximum of 9a–e
compared with 15a–d due to extended conjugation in the
latter compounds 15a–d. A substituent effect is also ob-
served in the 9a–e series, with electron-donating and -with-
drawing groups (9a: X = OCH3 and 9e: X = NO2) produc-
ing a slight redshift in the absorption with respect to 9c (X
= H).
Table 6. Summary of optical measurements and thermal properties
of 9a–e and 15a–d.
[a,b]
[c]
[d]
λabs [a][nm] (εmax λem
ΦFL
Tm
[°C]
Tdec
max
max
Figure 2. Absorption spectra of 15a–d in CH2Cl2.
[104 m–1 cm–1])
[nm]
[°C]
9a
388 (0.90)
386 (0.88)
386 (0.87)
387 (0.99)
400 (0.54)
487(0.18)
485 (0.37)
484 (0.32)
484 (0.58)
466
449
446
448
523
502
502
497
499
0.59
0.76
0.80
0.47
0.16
0.39
0.46
0.45
0.48
188
171
167
192
204
186
166
171
206
338
329
322
316
250
186
218
201
342
for 9a–d (with a value of 16% for 9e) and 39–48% for 15a–
d, respectively. Thus, molecules 9a–d show potential as
deep-blue emitters for organic light-emitting diode (OLED)
applications. In addition, the thermal properties of these
two series were determined by differential scanning calorim-
9b
9c
9d
9e
15a
15b
15c
15d
[a] Measured in CH2Cl2. [b] Excited at the absorption maximum.
[c] Norharman in 0.1 m H2SO4 (Φ330~390 = 0.58) was used as a
standard for the oxadisilole-fused 1H-benzo[f]indazoles 9a–e and
coumarin 6 in ethanol (Φ420 = 0.78) was used as a standard for 1H-
naphtho[2,3-f]indazoles 15a–d. [d] Determined by thermal gravi-
metric analysis at a heating rate of 10 °Cmin–1 under N2.
Figure 3. Emission spectra of 9a–e in CH2Cl2.
Figure 1. Absorption spectra of 9a–e in CH2Cl2.
The photoluminescence spectra of 9a–e and 15a–d in
CH2Cl2 show moderate-to-strong deep-blue to green emis-
sion with maxima in the range of 446–523 nm (Figures 3
and 4, Table 6). A similar substituent effect was also found
for the emission maximum in 9a–e, that is, the emission
maximum shifts to a longer wavelength for derivatives sub-
stituted with an electron-donating or -withdrawing group
(i.e., X = OCH3 or NO2) relative to that of 9c (X = H),
which allows the color emission of this series to be tuned.
The fluorescence quantum yields (Φ) measured in CH2Cl2
by using norharman as the reference for 9a–e and couma-
rin 6 as the reference for 15a–d are in the range of 47–80% Figure 4. Emission spectra of 15a–d in CH2Cl2.
3008 Eur. J. Org. Chem. 2013, 3005–3012
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Oxadisilole-Fused 1H-Benzo[f]- and 1H-Naphtho[2,3-f]indazoles
etry (DSC) and thermal gravimetric analysis (TGA) analy-
ses. In general, they show good thermal stability, particu-
larly 9a–d, over 300 °C and high melting points ranging
from 166 to 206 °C.
Experimental Section
General Methods: Purification was effected by silica gel column
chromatography (200–300 mesh silica gel) using mixtures of rea-
gent-grade EtOAc/petroleum ether (PE, 60–80 °C) as eluents.
NMR spectra were recorded with a Bruker DRX-500 NMR spec-
The redox properties as well as the HOMO (highest-oc-
cupied molecular orbital) and LUMO (lowest-unoccupied
molecular orbital) energy levels of 9a–e and 15a–d are tabu-
lated in Table 7. The redox properties of 9a–e and 15a–d
were studied by cyclic voltammetry in a three-electrode cell
in CH2Cl2 with 0.1 m of Bu4NPF6 as the supporting electro-
lyte. All of the potentials reported are referenced to Fc/Fc+
as standard. In contrast to the optical properties, the sub-
stituent on the 1-aryl ring has an insignificant effect on the
oxidation potential (Eox), which lies in the range of 1.28–
1.41 V for 9a–d (with 0.09 V for 9e) and 0.97–1.01 V for
15a–d. The HOMO energy values were calculated by the
equation of Janietz or Schmidt,[15,16a] and the LUMO en-
ergy levels were obtained by subtraction of the optical band
gap from the HOMO. Molecules within the same series,
that is, 9a–e or 15a–d, show similar HOMO energies. In
addition, the band gaps within the same series are also very
similar, with the exception of 9e, which has a smaller band
gap due to a larger redshift in the absorption spectrum.
1
trometer at 500 MHz for H and at 125 MHz for 13C with CDCl3
as solvent. Chemical shifts are reported in ppm on the δ scale rela-
tive to the residual resonance of CHCl3 (δ = 7.26 ppm for H and
1
77.16 ppm for the central peak of the triplet in 13C). Coupling con-
stants (J) are reported in Hz. IR spectra were recorded with an
FTIR spectrometer in KBr discs. Low-resolution mass spectra were
recorded with an Agilent spectrometer in EI or API-ES mode.
High-resolution mass spectra were recorded with a Waters Micro-
mass GCT instrument. Element analyses were performed at the
Shanghai University. The fluorescence quantum yields in solution
were determined by the dilution method using norharman
(Φ330–390 = 0.58) or coumarin 6 (Φ420 = 0.78) as standard. Thermal
stabilities were determined by thermal gravimetric analysis with a
heating rate of 10 °Cmin–1 under N2.
Synthesis of Cycloadducts 8a–e and 14a–e: Triethylamine (0.12 mL,
4.0 mmol in 6 mL chloroform) was added by means of a syringe to
a stirred mixture of compound 7 or 13 (1.0 mmol) and hydrazonoyl
chlorides 4a–e (2.0 mmol) in chloroform (12 mL) at 50 °C under
N2. The reaction mixture was stirred at 50 °C for 6 h and then the
solvent was removed under reduced pressure. The crude product
was purified by column chromatography on silica gel using a gradi-
ent of 5–10% EtOAc in PE (60–80 °C) as the eluent to afford cy-
cloadducts 8a–e and 14a–e.
Table 7. Oxidation potentials and HOMO and LUMO energy
levels of 9a–e and 15a–d.
[a]
Eox
HOMO[b]
[eV]
Band gap[c]
[eV]
LUMO[d]
[eV]
[V]
Methyl 1-(4-Methoxyphenyl)-6,7-[oxybis(dimethylsilanediyl)]-
3a,4,9,9a-tetrahydro-4,9-epoxy-1H-benzo[f]indazole-3-carboxylate
(8a): Yield 427 mg, 89%; yellow solid; m.p. 120–121 °C. H NMR
9a
1.28
1.34
1.37
1.41
0.90
0.97
0.98
1.01
1.01
–5.59
–5.65
–5.68
–5.72
–5.21
–5.28
–5.29
–5.32
–5.32
2.89
2.92
2.94
2.93
2.81
2.45
2.47
2.48
2.47
–2.70
–2.73
–2.74
–2.79
–2.40
–2.83
–2.82
–2.84
–2.85
9b
1
9c
(500 MHz, CDCl3): δ = 0.346 (s, 3 H, SiMe), 0.351 (s, 3 H, SiMe),
0.39 (s, 3 H, SiMe), 0.41 (s, 3 H, SiMe), 3.82 (s, 3 H, OMe), 3.91
(d, J = 9.0 Hz, 1 H, CH-C=), 3.92 (s, 3 H, OMe), 4.70 (d, J =
9.0 Hz, 1 H, CH-N), 5.72 (s, 1 H, CH-O), 5.73 (s, 1 H, CH-O),
6.93 (d, J = 9.0 Hz, 2 H, Ar-H), 7.23 (d, J = 9.0 Hz, 2 H, Ar-H),
7.59 (s, 2 H, Ar-H) ppm. 13C NMR (125 MHz, CDCl3): δ = 1.07,
1.15, 1.18, 1.3, 52.3, 55.5, 55.8, 69.8, 83.1, 83.5, 114.9, 115.0, 115.6,
122.5, 135.6, 135.7, 143.4, 146.3, 148.2, 148.9, 155.2, 163.4 ppm.
9d
9e
15a
15b
15c
15d
[a] Eox was estimated by CV in CH2Cl2 with a platinum disk as the
working electrode, a platinum wire as the counter electrode and
SCE as the reference electrode with an agar salt bridge connecting
the compound solution and ferrocene as an external standard, and
0.1 m TBAPF6 at a scan rate of 100 mV/s, E1/2(Fc/Fc+) = 0.49 V
vs. SCE, calculated with ferrocene (4.8 eV vs. vacuum). [b] HOMO
= Eox – [E1/2 (Fc/Fc+)] + 4.8. [c] Estimated from the absorption
edge in CH2Cl2. [d] LUMO = HOMO + Optical band gap.
IR (KBr): ν = 3436, 2954, 1697, 1512, 1449, 1250, 932, 792 cm–1.
˜
MS (API-ES): m/z (%) = 503.1 (35) [M + Na]+, 233.1 (100).
C24H28N2O5Si2 (480.67): calcd. C 59.97, H 5.87, N 5.83; found C
59.65, H 6.25, N 5.49.
Methyl 1-(4-Methylphenyl)-6,7-[oxybis(dimethylsilanediyl)]-
3a,4,9,9a-tetrhydro-4,9-epoxy-1H-benzo[f]indazole-3-carboxylate
(8b): Yield 362 mg, 78%; yellow solid; m.p. 152–153 °C. H NMR
1
(500 MHz, CDCl3): δ = 0.36 (s, 6 H, SiMe2), 0.40 (s, 3 H, SiMe),
0.42 (s, 3 H, SiMe), 2.34 (s, 3 H, Me), 3.91 (d, J = 9.5 Hz, 1 H,
CH-C=), 3.93 (s, 3 H, OMe), 4.71 (d, J = 9.5 Hz, 1 H, CH-N),
5.74 (s, 1 H, CH-O), 5.75 (s, 1 H, CH-O), 7.17–7.21 (m, 4 H, Ar-H),
7.60 (s, 1 H, Ar-H), 7.61 (s, 1 H, Ar-H) ppm. 13C NMR (125 MHz,
CDCl3): δ = 1.05, 1.14, 1.16, 1.3, 20.8, 52.3, 55.5, 69.4, 83.0, 83.5,
114.1, 122.5, 122.6, 130.1, 131.4, 136.2, 139.3, 143.4, 146.3, 148.2,
Conclusions
Two previously unknown series of oxadisilole-fused 1H-
benzo[f]indazoles 9a–e and 1H-naphtho[2,3-f]indazoles
15a–d have been synthesized, respectively, by the 1,3-dipolar
cycloaddition reactions of oxabicyclic alkenes 7 and 13
with nitrile imines 5a–e generated in situ from N-aryl-
hydrazonoyl chlorides 4a–e followed by deoxygenation/aro-
148.9, 163.4 ppm. IR (KBr): ν = 3442, 2955, 1710, 1518, 1447,
˜
1261, 933, 792 cm–1. MS (API-ES): m/z (%) = 487.0 (31) [M +
matization under mild conditions. The photophysical, redox Na]+, 217.1 (100). C24H28N2O4Si2 (464.67): calcd. C 62.06, H 6.07,
N 6.03; found C 61.96, H 5.88, N 5.87.
and thermal properties of the oxadisilole-fused 1H-
benzo[f]- and 1H-naphtho[2,3-f]indazoles have been charac-
terized. Compounds 9a–d show potential as deep-blue emit-
ters for OLED applications because of their high fluores-
cence quantum yields and thermal stabilities.
Methyl 1-Phenyl-6,7-[oxybis(dimethylsilanediyl)]-3a,4,9,9a-tetra-
hydro-4,9-epoxy-1H-benzo[f]indazole-3-carboxylate (8c): Yield
342 mg, 76%; yellow solid; m.p. 107–108 °C. H NMR (500 MHz,
CDCl3): δ = 0.359 (s, 3 H, SiMe), 0.360 (s, 3 H, SiMe), 0.40 (s, 3
1
Eur. J. Org. Chem. 2013, 3005–3012
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3009

Y. Chen, M. S. Wong et al.
133.0, 133.3, 136.4, 139.3, 139.7, 142.3, 163.4 ppm. IR (KBr): ν =
FULL PAPER
H, SiMe), 0.42 (s, 3 H, SiMe), 3.92 (d, J = 9.0 Hz, 1 H, CH-C=),
˜
3.93 (s, 3 H, OMe), 4.73 (d, J = 9.0 Hz, 1 H, CH-N), 5.75 (s, 1 H, 3443, 2951, 1682, 1510, 1279, 1166, 809 cm–1. MS (API-ES): m/z
CH-O), 5.76 (s, 1 H, CH-O), 7.03 (t, J = 7.0 Hz, 1 H, Ar-H), 7.28–
(%) = 407.1 (100) [M + Na]+. C24H20N2O3 (384.43): calcd. C 74.98,
7.31 (m, 2 H, Ar-H), 7.36–7.40 (m, 2 H, Ar-H), 7.60 (s, 1 H, Ar- H 5.24, N 7.29; found C 74.87, H 5.35, N 6.79.
H), 7.62 (s, 1 H, Ar-H) ppm. 13C NMR (125 MHz, CDCl3): δ =
1.05, 1.14, 1.16, 1.23, 52.3, 55.6, 69.3, 83.0, 83.5, 114.1, 121.9,
122.5, 122.6, 129.6, 137.0, 141.6, 143.3, 146.2, 148.3, 148.9,
Methyl 1-Phenyl-3a,4,11,11a-tetrahydro-4,11-epoxy-1H-
naphtho[2,3-f]indazole-3-carboxylate (14c): Yield 311 mg, 84%; yel-
low solid; m.p. 190–191 °C. 1H NMR (500 MHz, CDCl3): δ = 3.94
(d, J = 9.0 Hz, 1 H, CH-C=), 3.95 (s, 3 H, OMe), 4.72 (d, J =
9.0 Hz, 1 H, CH-N), 5.85 (s, 1 H, CH-O), 5.87 (s, 1 H, CH-O),
7.04 (t, J = 7.0 Hz, 1 H, Ar-H), 7.30–7.32 (m, 2 H, Ar-H), 7.38–
7.42 (m, 2 H, Ar-H), 7.52–7.54 (m, 2 H, Ar-H), 7.81 (s, 1 H, Ar-
H), 7.83 (s, 1 H, Ar-H), 7.86–7.87 (m, 2 H, Ar-H) ppm. 13C NMR
(125 MHz, CDCl3): δ = 52.4, 56.2, 69.5, 83.0, 83.5, 114.1, 119.0,
119.2, 121.9, 126.6, 126.7, 128.4, 128.6, 129.6, 133.0, 133.3, 137.2,
163.3 ppm. IR (KBr): ν = 3436, 2954, 1699, 1502, 1448, 1257, 931,
˜
792 cm–1. MS (API-ES): m/z (%) = 473.0 (59) [M + Na]+, 203.1
(100). C23H26N2O4Si2 (450.64): calcd. C 61.30, H 5.82, N 6.22;
found C 61.47, H 6.29, N 5.84.
Methyl 1-(4-Chlorophenyl)-6,7-[oxybis(dimethylsilanediyl)]-
3a,4,9,9a-tetrahydro-4,9-epoxy-benzo[f]indazole-3-carboxylate (8d):
Yield 359 mg, 74 %; yellow solid; m.p. 146–147 °C. 1H NMR
(500 MHz, CDCl3): δ = 0.35 (s, 6 H, SiMe2), 0.39 (s, 3 H, SiMe),
0.41 (s, 3 H, SiMe), 3.92 (d, J = 9.0 Hz, 1 H, CH-C=), 3.93 (s, 3
H, OMe), 4.67 (d, J = 9.0 Hz, 1 H, CH-N), 5.70 (s, 1 H, CH-O),
5.75 (s, 1 H, CH-O), 7.20 (J = 9.0 Hz, 2 H, Ar-H), 7.31–7.33 (m,
2 H, Ar-H), 7.60 (s, 1 H, Ar-H), 7.61 (s, 1 H, Ar-H) ppm. 13C
NMR (125 MHz, CDCl3): δ = 1.1, 1.15, 1.24, 52.5, 55.9, 69.3, 82.9,
83.3, 115.2, 122.56, 122.61, 126.9, 129.6, 137.7, 140.3, 143.1, 146.1,
139.6, 141.6, 142.3, 163.3 ppm. IR (KBr): ν = 3441, 2950, 1693,
˜
1503, 1264, 1117, 858, 745 cm–1. MS (API-ES): m/z (%) =
393.1 (100) [M + Na]+. HRMS (MALDI-TOF): calcd. for
C23H18N2O3Na [M + Na]+ 393.1210; found 393.1222.
Methyl 1-(4-Chlorophenyl)-3a,4,11,11a-tetrahydro-4,11-epoxy-1H-
naphtho[2,3-f]indazole-3-carboxylate (14d): Yield 271 mg, 67%; yel-
low solid; m.p. 168–170 °C. 1H NMR (500 MHz, CDCl3): δ = 3.91
(d, J = 9.0 Hz, 1 H, CH-C=), 3.94 (s, 3 H, OMe), 4.63 (d, J =
9.0 Hz, 1 H, CH-N), 5.78 (s, 1 H, CH-O), 5.85 (s, 1 H, CH-O),
7.20 (d, J = 9.0 Hz, 2 H, Ar-H), 7.33 (d, J = 9.0 Hz, 2 H, Ar-H),
7.51–7.53 (m, 2 H, Ar-H), 7.80 (d, J = 9.0 Hz, 2 H, Ar-H), 7.84–
7.86 (m, 2 H, Ar-H) ppm. 13C NMR (125 MHz, CDCl3): δ = 52.5,
56.4, 69.5, 82.9, 83.2, 115.2, 119.1, 119.3, 126.7, 126.8, 126.9, 128.4,
128.6, 129.6, 133.0, 133.3, 137.8, 139.3, 140.3, 142.1, 163.1 ppm.
148.4, 149.1, 163.1 ppm. IR (KBr): ν = 3443, 2953, 1731, 1549,
˜
1495, 1239, 929, 790 cm–1. MS (API-ES): m/z (%) = 507.0 (100) [M
+ Na]+. C23H25ClN2O4Si2 (485.09): calcd. C 56.95, H 5.19, N 5.78;
found C 56.55, H 5.24. N 5.74.
Methyl 1-(4-Nitrophenyl)-6,7-[oxybis(dimethylsilanediyl)]-3a,4,9,9a-
tetrahydro-4,9-epoxy-1H-benzo[f]indazole-3-carboxylate (8e): Yield
1
287 mg, 58%; yellow solid; m.p. 170–171 °C. H NMR (500 MHz,
IR (KBr): ν = 3442, 2952, 1686, 1496, 1288, 1166, 859 cm–1. MS
˜
CDCl3): δ = 0.359 (s, 3 H, SiMe), 0.363 (s, 3 H, SiMe), 0.39 (s, 3
H, SiMe), 0.42 (s, 3 H, SiMe), 3.97 (s, 3 H, OMe), 3.98 (d, J =
9.0 Hz, 1 H, CH-C=), 4.73 (d, J = 9.0 Hz, 1 H, CH-N), 5.73 (s, 1
H, CH-O), 5.78 (s, 1 H, CH-O), 7.31 (d, J = 9.0 Hz, 2 H, Ar-H),
7.61 (s, 1 H, Ar-H), 7.65 (s, 1 H, Ar-H), 8.27 (d, J = 9.0 Hz, 2 H,
Ar-H) ppm. 13C NMR (125 MHz, CDCl3): δ = 1.1, 1.17, 1.23, 52.8,
56.6, 69.0, 82.7, 83.1, 113.3, 122.7, 122.8, 126.1, 141.7, 142.6, 145.8,
(API-ES): m/z (%) = 427.0 (100) [M + Na]+. HRMS (MALDI-
TOF): calcd. for C23H17ClN2O3Na [M + Na]+ 427.0820; found
427.0834.
Methyl 1-(4-Nitrophenyl)-3a,4,11,11a-tetrahydro-4,11-epoxy-1H-
naphtho[2,3-f]indazole-3-carboxylate (14e): Yield 203 mg, 49% yel-
low solid; m.p. 211–212 °C. 1H NMR (500 MHz, CDCl3): δ = 3.99
(s, 3 H, OMe), 4.01 (d, J = 8.5 Hz, 1 H, CH-C=), 4.75 (d, J =
8.5 Hz, 1 H, CH-N), 5.84 (s, 1 H, CH-O), 5.90 (s, 1 H, CH-O),
7.34 (d, J = 9.0 Hz, 2 H, Ar-H), 7.55–7.56 (m, 2 H, Ar-H), 7.85 (s,
1 H, Ar-H), 7.89 (s, 3 H, Ar-H), 8.30 (d, J = 9.0 Hz, 2 H, Ar-
H) ppm. 13C NMR (125 MHz, CDCl3): δ = 52.9, 57.1, 69.2, 82.7,
83.1, 113.3, 119.4, 119.6, 126.2, 126.9, 127.0, 128.5, 128.6, 133.1,
146.6, 147.6, 148.8, 149.5, 162.6 ppm. IR (KBr): ν = 3439, 2956,
˜
1729, 1599, 1336, 930, 792 cm–1. MS (API-ES): m/z = 496.1 (100)
[M + H]+. HRMS (MALDI-TOF): calcd. for C23H25N3O6Si2 [M
+ H]+ 496.1368; found 496.1355.
Methyl 1-(4-Methoxyphenyl)-3a,4,11,11a-tetrahydro-4,11-epoxy-
1H-naphtho[2,3-f]indazole-3-carboxylate (14a): Yield 312 mg, 78%;
yellow solid; m.p. 170–171 °C. 1H NMR (500 MHz, CDCl3): δ =
3.83 (s, 3 H, OMe), 3.94 (d, J = 9.5 Hz, 1 H, CH-C=), 3.96 (s, 3
H, OMe), 4.72 (d, J = 9.5 Hz, 1 H, CH-N), 5.83 (s, 1 H, CH-O),
5.86 (s, 1 H, CH-O), 6.96 (d, J = 8.5 Hz, 2 H, Ar-H), 7.25 (d, J =
8.5 Hz, 2 H, Ar-H), 7.51–7.53 (m, 2 H, Ar-H), 7.81–7.87 (m, 4 H,
Ar-H) ppm. 13C NMR (125 MHz, CDCl3): δ = 52.2, 55.7, 56.0,
70.0, 83.0, 83.5, 115.0, 115.5, 118.9, 119.1, 126.5, 126.6, 128.3,
128.5, 133.0, 133.3, 135.5, 135.9, 139.6, 142.3, 155.2, 163.4 ppm.
133.4, 138.8, 141.6, 141.7, 141.8, 146.7, 162.6 ppm. IR (KBr): ν =
˜
3440, 2924, 1594, 1321, 1289, 1110, 844 cm–1. MS (API-ES): m/z
(%) = 416.1 (76) [M + H]+, 268.0 (100). HRMS (MALDI-TOF):
calcd. for C23H17N3O5[M + H]+ 416.1237; found 416.1241.
Synthesis of Methyl 1-Aryl-6,7-[oxybis(dimethylsilanediyl)]-1H-
benzo[f]indazole-3-carboxylates 9a–e by the Deoxygenation of 8a–e:
LiAlH4 (285 mg, 7.5 mmol) was added to a mixture of 8a–e
(0.25 mmol), TiCl4 (15 mL, 15 mmol) and Et3N (1.05 mL,
7.5 mmol) in dichloromethane (20 mL) at room temp. under N2.
The reaction mixture was stirred at this temperature for 24 h and
then poured into iced water (100 mL). The resulting mixture was
extracted with CH2Cl2 (2ϫ30 mL). The organic extract was dried
with anhydrous MgSO4, filtered and concentrated under reduced
pressure. The crude product was purified by column chromatog-
raphy on silica gel using a gradient of 10–15% EtOAc in PE (60–
80 °C) as eluent to afford the products 9a–e.
IR (KBr): ν = 3434, 2948, 1721, 1510, 1239, 1166, 826 cm–1. MS
˜
(API-ES): m/z (%) = 423.0 (100) [M + Na]+. HRMS (MALDI-
TOF): calcd. for C24H20N2O4Na [M + Na]+ 423.1315; found
423.1328.
Methyl 1-(4-Methylphenyl)-3a,4,11,11a-tetrahydro-4,11-epoxy-1H-
naphtho[2,3-f]indazole-3-carboxylate (14b): Yield 342 mg, 89%; yel-
low solid; m.p. 186–187 °C. 1H NMR (500 MHz, CDCl3): δ = 2.35
(s, 3 H, Me), 3.90 (d, J = 9.0 Hz, 1 H, CH-C=), 3.94 (s, 3 H, OMe),
4.68 (d, J = 9.0 Hz, 1 H, CH-N), 5.83 (s, 1 H, CH-O), 5.86 (s, 1 Methyl 1-(4-Methoxyphenyl)-6,7-[oxybis(dimethylsilanediyl)]-1H-
H, CH-O), 7.20 (s, 4 H, Ar-H), 7.51–7.53 (m, 2 H, Ar-H), 7.79 (s, benzo[f]indazole-3-carboxylate (9a): Yield 69 mg, 60%; yellow solid;
1 H, Ar-H), 7.81 (s, 1 H, Ar-H), 7.85–7.87 (m, 2 H, Ar-H) ppm.
m.p. 187–188 °C. 1H NMR (500 MHz, CDCl3): δ = 0.44 (s, 6 H,
SiMe2), 0.46 (s, 6 H, SiMe2), 3.91 (s, 3 H, OMe), 4.13 (s, 3 H,
13C NMR (125 MHz, CDCl3): δ = 20.8, 52.3, 56.0, 69.7, 83.0, 83.5,
114.2, 119.0, 119.2, 126.55, 126.64, 128.4, 128.5, 130.1, 131.5, OMe), 7.11 (d, J = 9.0 Hz, 2 H, Ar-H), 7.74 (d, J = 9.0 Hz, 2 H,
3010
www.eurjoc.org
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2013, 3005–3012

Oxadisilole-Fused 1H-Benzo[f]- and 1H-Naphtho[2,3-f]indazoles
Ar-H), 8.13 (s, 1 H, Ar-H), 8.17 (s, 1 H, Ar-H), 8.32 (s, 1 H, Ar-
was extracted with CH2Cl2 (2ϫ230 mL). The organic extract was
H), 8.92 (s, 1 H, Ar-H) ppm. 13C NMR (125 MHz, CDCl3): δ = dried with anhydrous MgSO4, filtered and concentrated under re-
1.3, 1.4, 52.4, 55.8, 106.9, 114.9, 121.9, 124.7, 125.5, 130.8, 131.6,
132.7, 133.05, 133.14, 136.5, 139.3, 142.1, 144.5, 159.4, 163.2 ppm.
duced pressure. The crude product was purified by column
chromatography on silica gel using a gradient of 10–15% EtOAc
in PE (60–80 °C) as the eluent to afford the products 15a–d.
IR (KBr): ν = 3446, 2955, 1737, 1516, 1252, 933, 792 cm–1. MS
˜
(EI): m/z (%) = 462.2 (100) [M]+. HRMS (EI): calcd. for
Methyl 1-(4-Methoxyphenyl)-1H-naphtho[2,3-f]indazole-3-carboxyl-
ate (15a): Yield 41 mg, 43 %; yellow solid; m.p. 185–187 °C. 1H
NMR (500 MHz, CDCl3): δ = 3.93 (s, 3 H, OMe), 4.14 (s, 3 H,
OMe), 7.13 (d, J = 8.0 Hz, 2 H), 7.40 (s, 2 H), 7.76 (d, J = 8.0 Hz,
2 H), 7.93 (d, J = 7.0 Hz, 1 H, Ar-H), 7.99 (d, J = 7.0 Hz, 1 H,
Ar-H), 8.28 (s, 1 H, Ar-H), 8.53 (s, 1 H, Ar-H), 8.73 (s, 1 H, Ar-
H), 9.13 (s, 1 H, Ar-H) ppm. 13C NMR (125 MHz, CDCl3): δ =
52.5, 55.8, 105.5, 114.9, 121.9, 124.9, 125.1, 125.4, 125.9, 126.0,
128.0, 128.2, 128.5, 129.3, 131.1, 132.4, 132.9, 136.3, 138.8, 159.2,
C24H26N2O4Si2 [M]+ 462.1431; found 462.1435.
Methyl 1-(4-Methylphenyl)-6,7-[oxybis(dimethylsilanediyl)]-1H-
benzo[f]indazole-3-carboxylate (9b): Yield 70 mg, 63%; yellow solid;
m.p. 170–171 °C. 1H NMR (500 MHz, CDCl3): δ = 0.45 (s, 6 H,
SiMe2), 0.47 (s, 6 H, SiMe2), 2.47 (s, 3 H, Me), 4.13 (s, 3 H, OMe),
7.39 (d, J = 8.0 Hz, 2 H, Ar-H), 7.73 (d, J = 8.0 Hz, 2 H, Ar-H),
8.18 (s, 1 H, Ar-H), 8.20 (s, 1 H, Ar-H), 8.32 (s, 1 H, Ar-H), 8.93
(s, 1 H, Ar-H) ppm. 13C NMR (125 MHz, CDCl3): δ = 1.3, 1.4,
21.3, 52.4, 107.1, 121.9, 123.6, 124.8, 130.3, 130.8, 131.7, 133.0,
133.1, 136.7, 137.2, 137.9, 138.9, 142.0, 144.4, 163.1 ppm. IR
163.2 ppm. IR (KBr): ν = 3443, 2923, 1715, 1516, 1255, 834,
˜
797 cm–1. MS (API-ES): m/z (%) = 382.2 (100) [M]+. HRMS (EI):
calcd. for C24H18N2O3 [M]+ 382.1317; found 382.1314.
(KBr): ν = 3455, 2953, 1749, 1518, 1252, 928, 790 cm–1. MS (EI):
˜
m/z (%) = 446.2 (7) [M]+, 191.2 (100). HRMS (EI): calcd. for
Methyl 1-(4-Methylphenyl)-1H-naphtho[2,3-f]indazole-3-carboxyl-
ate (15b): Yield 63 mg, 69 %; yellow solid; m.p. 165–166 °C. 1H
NMR (500 MHz, CDCl3): δ = 2.49 (s, 3 H, Me), 4.15 (s, 3 H,
OMe), 7.39–7.43 (m, 4 H, Ar-H), 7.77 (d, J = 8.0 Hz, 2 H, Ar-H),
7.94 (d, J = 8.0 Hz, 1 H, Ar-H), 7.99–8.01 (m, 1 H, Ar-H), 8.36 (s,
1 H, Ar-H), 8.55 (s, 1 H, Ar-H), 8.74 (s, 1 H, Ar-H), 9.15 (s, 1 H,
Ar-H) ppm. 13C NMR (125 MHz, CDCl3): δ = 21.4, 52.5, 105.7,
122.0, 123.6, 125.1, 125.2, 125.95, 126.04, 128.0, 128.2, 128.5,
129.3, 130.3, 131.1, 132.4, 136.6, 137.4, 137.8, 138.5, 163.2 ppm.
C24H26N2O3Si2 [M]+ 446.1482; found 446.1485.
Methyl 1-Phenyl-6,7-[oxybis(dimethylsilanediyl)]-1H-benzo[f]-
indazole-3-carboxylate (9c): Yield 51 mg, 47%; yellow solid; m.p.
166–167 °C. 1H NMR (500 MHz, CDCl3): δ = 0.45 (s, 6 H, SiMe2),
0.47 (s, 6 H, SiMe2), 4.14 (s, 3 H, OMe), 7.45–7.48 (m, 1 H, Ar-
H), 7.59–7.63 (m, 2 H, Ar-H), 7.87–7.89 (m, 2 H, Ar-H), 8.19 (s, 1
H, Ar-H), 8.24 (s, 1 H, Ar-H), 8.32 (s, 1 H, Ar-H), 8.94 (s, 1 H,
Ar-H) ppm. 13C NMR (125 MHz, CDCl3): δ = 1.3, 1.4, 52.4, 107.1,
122.1, 123.7, 124.9, 127.9, 129.8, 130.9, 131.7, 133.0, 133.2, 137.1,
IR (KBr): ν = 3443, 2956, 2924, 2854, 1716, 1517, 1261, 819 cm–1.
˜
MS (API-ES): m/z (%) = 366.2 (2) [M]+, 57.2 (100). HRMS (EI):
138.9, 139.7, 142.2, 144.6, 163.1 ppm. IR (KBr): ν = 3442, 2953,
˜
calcd. for C24H18N2O2 [M]+ 366.1368; found 366.1372.
1719, 1505, 1252, 931, 791 cm–1. MS (EI): m/z (%) = 432.2 (100)
[M]+. C23H24N2O3Si2 (432.63): calcd. C 63.85, H 5.59, N 6.48;
found C 63.55, H 5.638, N 6.275.
Methyl 1-Phenyl-1H-naphtho[2,3-f]indazole-3-carboxylate (15c):
Yield 57 mg, 65 %; yellow solid; m.p. 170–171 °C. 1H NMR
(500 MHz, CDCl3): δ = 4.14 (s, 3 H, OMe), 7.37–7.42 (m, 2 H, Ar-
H), 7.45–7.48 (m, 1 H, Ar-H), 7.60–7.64 (m, 2 H, Ar-H), 7.88–7.98
(m, 4 H, Ar-H), 8.33 (s, 1 H, Ar-H), 8.51 (s, 1 H, Ar-H), 8.68 (s, 1
H, Ar-H), 9.09 (s, 1 H, Ar-H) ppm. 13C NMR (125 MHz, CDCl3):
δ = 52.5, 105.6, 122.0, 123.5, 125.1, 125.2, 125.95, 126.01, 127.7,
128.0, 128.2, 128.5, 129.2, 129.8, 131.06, 131.09, 132.4, 136.9,
Methyl 1-(4-Chlorophenyl)-6,7-[oxybis(dimethylsilanediyl)]-1H-
benzo[f]indazole-3-carboxylate (9d): Yield 78 mg, 67%; yellow solid;
m.p. 191–193 °C. 1H NMR (500 MHz, CDCl3): δ = 0.45 (s, 6 H,
SiMe2), 0.47 (s, 6 H, SiMe2), 4.13 (s, 3 H, OMe), 7.56 (d, J =
8.0 Hz, 2 H, Ar-H), 7.81 (d, J = 8.0 Hz, 2 H, Ar-H), 8.18 (s, 1 H,
Ar-H), 8.19 (s, 1 H, Ar-H), 8.32 (s, 1 H, Ar-H), 8.93 (s, 1 H, Ar-
H) ppm. 13C NMR (125 MHz, CDCl3): δ = 1.3, 1.4, 52.5, 106.8,
122.3, 124.6, 124.8, 129.9, 130.9, 131.6, 133.0, 133.3, 133.4, 137.4,
138.2, 139.9, 163.1 ppm. IR (KBr): ν = 3451, 2957, 2925, 2854,
˜
1716, 1504, 1262, 804 cm–1. MS (API-ES): m/z (%) = 352.2 (100)
[M]+. HRMS (EI): calcd. for C23H16N2O2 [M]+ 352.1212; found
352.1215.
138.2, 138.6, 142.5, 144.9, 162.9 ppm. IR (KBr): ν = 3474, 2956,
˜
1730, 1252, 939, 785 cm–1. MS (EI): m/z (%) = 466.1 (100)
[M]+. HRMS (EI): calcd. for C23H23N2O3Si2Cl [M]+ 466.0936;
found 466.0937.
Methyl 1-(4-Chlorophenyl)-1H-naphtho[2,3-f]indazole-3-carboxylate
1
(15d): Yield 60 mg, 62%; yellow solid; m.p. 205–206 °C. H NMR
(500 MHz, CDCl3): δ = 4.16 (s, 3 H, OMe), 7.41–7.44 (m, 2 H, Ar-
H), 7.60 (d, J = 8.5 Hz, 2 H, Ar-H), 7.86 (d, J = 8.5 Hz, 2 H, Ar-
H), 7.96 (d, J = 8.0 Hz, 1 H, Ar-H), 8.01 (d, J = 8.0 Hz, 1 H, Ar-
H), 8.35 (s, 1 H, Ar-H), 8.57 (s, 1 H, Ar-H), 8.75 (s, 1 H, Ar-H),
9.15 (s, 1 H, Ar-H) ppm. 13C NMR (125 MHz, CDCl3): δ = 52.6,
105.4, 122.3, 124.4, 124.9, 125.3, 126.0, 126.1, 128.0, 128.2, 128.5,
129.2, 129.9, 131.0, 131.2, 132.5, 133.1, 137.3, 138.0, 138.4,
Methyl 1-(4-Nitrophenyl)-6,7-[oxybis(dimethylsilanediyl)]-1H-
benzo[f]indazole-3-carboxylate (9e): Yield 22 mg, 18%; yellow solid;
m.p. 203–205 °C. 1H NMR (500 MHz, CDCl3): δ = 0.43 (s, 6 H,
SiMe2), 0.46 (s, 6 H, SiMe2), 4.12 (s, 3 H, OMe), 6.86 (d, J =
8.5 Hz, 2 H, Ar-H), 7.57 (d, J = 8.5 Hz, 2 H, Ar-H), 8.10 (s, 1 H,
Ar-H), 8.15 (s, 1 H, Ar-H), 8.31 (s, 1 H, Ar-H), 8.91 (s, 1 H, Ar-
H) ppm. 13C NMR (125 MHz, CDCl3): δ = 1.3, 1.4, 52.4, 107.0,
115.6, 121.8, 124.6, 125.6, 130.7, 130.8, 131.7, 133.0, 133.1, 136.0,
162.9 ppm. IR (KBr): ν = 3442, 2960, 2919, 2850, 1721, 1500, 1261,
˜
800 cm–1. MS (EI): m/z (%) = 386.2 (100) [M]+. HRMS (EI): calcd.
139.4, 141.9, 144.2, 146.6, 163.3 ppm. IR (KBr): ν = 3455, 3360,
˜
for C23H15N2O2Cl [M]+ 386.0822; found 386.0818.
2955, 1720, 1521, 932, 793 cm–1. MS (EI): m/z (%) = 477.3 (1) [M]+,
447.2 (100). HRMS (EI): calcd. for C23H23N3O5Si2 [M]+ 477.1176;
found 477.1178.
Supporting Information (see footnote on the first page of this arti-
cle): 1H and 13C NMR spectra of compounds 8a–e, 9a–e, 14a–e
and 15a–d.
Synthesis of Methyl 1-Aryl-1H-naphtho[2,3-f]indazole-3-carboxyl-
ates 15a–d by the Deoxygenation of 14a–d: LiAlH4 (285 mg,
7.5 mmol) was added to a mixture of 14a–e (0.25 mmol), TiCl4
(15 mL, 15 mmol) and Et3N (1.05 mL, 7.5 mmol) in dichlorometh-
ane (20 mL) at 40 °C under N2 and the mixture was stirred at this
temperature for 1 h. After cooling to room temperature, the mix-
ture was poured into iced water (100 mL) and the resulting mixture
Acknowledgments
Financial support from the National Natural Science Foundation
of China (NSFC) (grant numbers 21272146 and 20872086) is ac-
knowledged.
Eur. J. Org. Chem. 2013, 3005–3012
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3011

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Received: January 21, 2013
Published Online: April 4, 2013
3012
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© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2013, 3005–3012