One-pot heterocyclic ring closure of 1,1′-bi-2-naphthol to 7H-dibenzo[c,g]carbazole

Article abstract of DOI:10.1016/j.tetlet.2017.11.054

An operationally simple ring closure of racemic 1,1′-bi-2-naphthol (BINOL) yielded the heterocyclic aromatic compound 7H-dibenzo[c,g]carbazole (DBC). This one-pot method gave a good conversion and is suitable for gram-scale synthesis. DBC derivatives have high thermal durability, amorphous and crystalline structures with unique morphological properties, and semi-conducting behavior with potential applications in organic electronics.

Full text of DOI:10.1016/j.tetlet.2017.11.054

Accepted Manuscript
One-pot heterocyclic ring closure of 1,1'-bi-2-naphthol to 7H-dibenzo[c,g]car-
bazole
Fathy Hassan, Masuki Kawamoto, Krishnachary Salikolimi, Daisuke
Hashizume, Takuji Hirose, Yoshihiro Ito
PII:
S0040-4039(17)31488-0
https://doi.org/10.1016/j.tetlet.2017.11.054
TETL 49497
DOI:
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
11 October 2017
23 November 2017
28 November 2017
Please cite this article as: Hassan, F., Kawamoto, M., Salikolimi, K., Hashizume, D., Hirose, T., Ito, Y., One-pot
heterocyclic ring closure of 1,1'-bi-2-naphthol to 7H-dibenzo[c,g]carbazole, Tetrahedron Letters (2017), doi: https://
doi.org/10.1016/j.tetlet.2017.11.054
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2
a,b
*,a,b,c,d
a
e
b
Fathy Hassan , Masuki Kawamoto
, Krishnachary Salikolimi , Daisuke Hashizume , Takuji Hirose , and
*
a,c
Yoshihiro Ito

1
Tetrahedron Letters
One-pot heterocyclic ring closure of 1,1'-bi-2-naphthol to 7H-dibenzo[c,g]carbazole
a,b
,a,b,c,d
a
e
b
Fathy Hassan , Masuki Kawamoto
, Krishnachary Salikolimi , Daisuke Hashizume , Takuji Hirose ,
,a,c
and Yoshihiro Ito*
a
Emergent Bioengineering Materials Research Team, RIKEN Center for Emergent Matter Science (CEMS), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama 338-8570, Japan
b
c
Nano Medical Engineering Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
d
Photocatalysis International Research Center, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
e
Materials Characterization Support Unit, RIKEN Center for Emergent Matter Science (CEMS), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
An operationally simple ring closure of racemic 1,1'-bi-2-naphthol (BINOL) yielded the
heterocyclic aromatic compound 7H-dibenzo[c,g]carbazole (DBC). This one-pot method gave a
good conversion and is suitable for gram-scale synthesis. DBC derivatives have high thermal
durability, amorphous and crystalline structures with unique morphological properties, and
semi-conducting behavior with potential applications in organic electronics.
Available online
2
009 Elsevier Ltd. All rights reserved
Keywords:
7
H-Dibenzo[c,g]carbazole
Heterocyclic ring closure
,1'-Bi-2-naphthol
Functional materials
1
7H-Dibenzo[c,g]carbazole (DBC) is a heterocyclic aromatic
3
(NH aq.) in an autoclave results in condensation of the initially
compound that is important in toxicology, pharmacology, and
pharmaceuticals. DBC derivatives, which are used as standard
reagents, show a broad range of biological and carcinogenic
formed 2-amino-2'-hydroxy-1,1'-binaphthyl (NOBIN) to furnish
DBC. The gram-scale synthesis of DBC, with an isolated yield of
96%, using this method represents a cost-effective one-pot
procedure for DBC synthesis. N-Alkylated and N-arylated DBCs
were also synthesized in order to explore their potential use as
optoelectronic materials.
1
activities. Exposure of various tissues, including skin, liver,
lung, and stomach, to DBC has caused tumors in several
2
experimental animals. On the other hand, aromatic DBC
compounds have recently attracted particular interest as
During a study of the amidation of racemic BINOL (1) to
racemic NOBIN (2), we found that DBC (3) was produced when
semiconducting materials for organic light-emitting diodes
8
3
(OLEDs).
1
and the aminating reagent (AR) (NH
(AR:NH aq. = 1:2.6 mol/mol) were heated at 200 ºC in an
autoclave (Scheme 1). The conversions of the resulting
4 2 3 2 3
) SO ·H O in NH aq.
Despite the diverse applications of DBC derivatives, there are
few efficient procedures for their synthesis. Lieber and co-
3
workers synthesized DBC via lithium desulfurization of 7H-
dibenzo[c,h]phenothiazine, with a yield of 33%. The acid-
catalyzed reaction of 2,2'-hydrazonaphthalene gave DBC in only
compounds were monitored using chiral high-performance liquid
chromatography (HPLC); the elution times for 3, (R)-2, and (S)-2
were 6, 11, and 22 min, respectively. Isolated yields were
determined after separation by recrystallization from benzene.
4
5
% yield as a by-product with 2,2'-diamino-1,1'-binaphthyl
5
(BINAM). Alkylated DBCs can be obtained in low yield (~5%)
by Fisher indole synthesis and subsequent dehydrogenation over
6
chloronil or palladium on activated charcoal. Recently, Lim and
co-workers reported the acid-catalyzed condensation of BINAM
7
to give DBC with a good yield of 85%. However, commercially
−1
available DBC is still expensive (US$19.1 mg , Sigma-Aldrich),
therefore its practical use is limited.
Scheme 1. Synthesis of DBC from rac-BINOL
In this study, we report that the one-step ring closure of 1,1'-
bi-2-naphthol (BINOL) gives DBC with a 99% conversion.
Optimization of the reaction time and the 1:AR ratio led to an
increase in the conversion of 3 (Table 1 and ESI). Initially, the
−
1
Simple heating of racemic BINOL (US¢0.3 mg , Sigma-
Ald —r ic —h ) with (NH SO ·H O and an aqueous ammonia solution
—
)
4 2
3
2

Corresponding author. Tel.: +81-48-467-2752; fax: +81-48-467-9300; e-mail: mkawamot@riken.jp (M. Kawamoto), y-ito@riken.jp (Y. Ito)

2
Tetrahedron
conversion of 3 was only 12% for 1:AR = 1:10 (Entry 1). The
conversion was improved upon increasing the 1:AR ratio or
reaction time (Entries 2 and 3). Adjustment of the reaction time
and reagent ratio resulted in the conversion increasing from 12%
resonance-stabilized proton adducts, addition of a bisulfite anion
affords tetralonesulfonic acid to form tetraloniminesulfonic acids
after amidation. Subsequently cyclization and elimination of
sulfurous acid occurs to yield 3.
(
Entry 1) to 27% (Entry 4). Extending the reaction time from 6 d
We also examined the ring-closure behavior of 2 and its
analogues (Fig. 1): rac-6,6'-dibromo-2-amino-2'-hydroxy-1,1'-
binaphthyl (2a), and 2-amino-2'-hydroxy-1,1'-biphenyl (4) in
order to clarify the reactivity of the DBC structure (Table 2). The
reaction in the presence of 2:AR = 1:24 (mol/mol) at 200 ºC for
to 10 d led to the efficient formation of 3 (Entry 5). Increasing
the 1:AR ratio was effective for obtaining high conversions
(Entries 5–7): a conversion of 81% was obtained using 1:AR =
1
:36 (Entry 7). However, the conversion gradually became
saturated even when the amount of AR was increased. We
suggest that this saturation is caused by AR consumption. For
entry 8, one-half of the AR was used for the first 5 d, and then
the remaining AR was added and the reaction continued for a
further 5 d. This strategy gave a conversion greater than 90%.
Almost complete reaction occurred in the presence of 1:AR =
1
9
2
10 d gave 3 with a conversion of 99% (Entry 1). The conversion
decreased when 2 was reacted at 190 ºC for 10 d (Entry 2). The
ring closure of compound 2a under the same reaction conditions
afforded 3,11-dibromo-7H-dibenzo[c,g]carbazole (3a) with a
conversion of 60% along with unidentified compounds (7%)
(
Entry 3). The ring-closure reaction at 200 ºC yielded insoluble
brown solids, resulting from thermal decomposition of 2a (Entry
). Thermogravimetric analysis (TGA) at a scanning rate of 10 ºC
:32 for 12 d, with a conversion of >99% and an isolated yield of
6% (Entry 9). Finally, increasing the reaction temperature to
20 ºC permitted the reaction time to be shortened to 8 d; the
4
−1
min under nitrogen showed that the weight loss of 2a at 200 ºC
was 7.6%. In contrast, a weight loss of only 1.3% was observed
for 2 at 200 ºC using the same scanning rate.
isolated yield was 96% (Entry 10).
Table 1. Optimization of the reaction conditions for 1 → 3
Conversion
(%)
Isolated b
a
Reaction
time (d)
1:AR
(mol/mol)
yield (%)
Entry
2
3
2
3
1
2
3
4
5
6
7
8
5
1:10
1:12
1:10
1:12
1:12
1:24
1:36
88
83
82
73
37
23
19
6
12
17
18
27
63
77
81
94
99
99
85
77
75
70
36
21
18
4
8
5
13
15
25
58
76
77
90
96
96
6
6
Figure 1. Structures of NOBIN analogues: 2a and 4, and their ring-
closed structures: 3a and 5, respectively.
10
10
10
10
12
8
The ring closure of 4 to give 9H-carbazole (5) afforded
mixtures; the conversions of 5 (45%), 4 (50%), and unknown
compounds (5%) were obtained using HPLC analysis (Entry 5)
c
1:24
(see ESI). These results suggest that the resonance structures of
c
d
9
1:32
1
-
the proton adduct are essential for ring closure. A possible
mechanism for this transformation is shown in the ESI (Scheme
S2). Compound 2 gives four resonance structures, but only two
resonance structures of 4 are involved in the synthesis of 5. The
low conversion of ring-closure may be the result of less
resonance-stabilized proton adducts. In future studies, the ring
closure of other NOBIN derivatives will be performed to clarify
the reaction mechanism.
e
c
d
1
0
1:32
1
-
a
b
c
d
e
Determined by chiral HPLC (ESI).
After recrystallization from benzene.
One-half of the AR was added for each half reaction time.
Not determined.
Reaction temperature: 220 ºC.
We then investigated the gram-scale synthesis of 3 using the
experimental conditions outlined in entry 10. The reaction of 1
3.0 g), (NH SO ·H O (44.8 g), and NH aq. (60 mL) in a 100
mL autoclave yielded 3 (2.7 g) with an isolated yield of 96%.
This reaction method is suitable for large-scale synthesis; HPLC
showed a high conversion of 3, i.e., >99%. Furthermore, the
purification step was simple. Because 3 was soluble in benzene,
whereas 2 precipitated, further chromatographic separation was
unnecessary. This one-pot process is expected to enable the
efficient large-scale synthesis of DBC.
a
Table 2. Heterocyclic ring-closure of 2 and its analogues
Reaction
(
)
4 2
3
2
3
Starting
material
Conversion
temperature
Entry
Product
a
(%)
(
ºC)
1
2
3
4
5
2
3
200
190
190
200
200
99
73
60
2
3
2a
2a
4
3a
b
b
-
-
5
45
A possible mechanism for the ring closure reaction is shown
in the ESI (Scheme S1). The first step is expected to be the
amidation of 1 to 2 then ring closure of 2 to give 3 followed by
a
Reagents and conditions: starting material:AR = 1:24 (mol/mol), heated for
10 d in autoclave.
9
b
the Bucherer carbazole reaction. Electrophilic addition of a
Not observed.
proton to the high electron density carbon atom in 2 gives

3
Table 3. Thermal, optical, and electrical data for DBC derivatives
abs
em
T
10
T
g
T
c
T
m
λ
max
λ
max
HOMO
LUMO
(eV)
E
g
a
Φ
f
b
c
(ºC)
(ºC)
28
(ºC)
(ºC)
(nm)
(nm)
(eV)
(eV)
3.22
3.22
3.13
2.60
d
d
3
6
6
6
322
321
324
363
-
-
277, 300, 347, 365
282, 305, 352, 370
280, 305, 350, 367
278, 302, 347, 364, 380 (sh)
372, 391, 408 (sh)
379, 394, 418 (sh)
376, 392, 413 (sh)
0.66
-5.67
-5.84
-5.62
-5.96
-2.45
-2.62
-2.49
-3.36
a
b
c
-2
78
113
197
235
0.42
74
143
0.44
d
d
d
-
-
-
< 0.001
a
b
c
d
f
Quinine sulfate (Φ : 0.546 in 1 N sulfuric acid) as the standard.
Determined using PESA.
Obtained from Tauc plot.
Not determined.
The DSC profiles show that compound 6c gave a sharp peak
−1
corresponding to the T
m g
at 235 ºC (ΔΗ: 30 kJ mol ), without a T
and T , in the third heating cycle. Needle-like single crystals of
c
maximum average width 0.1 mm and length 6.5 mm were
obtained using a liquid-phase crystal-growth method (Fig. 3c).
Compound 6c crystallized in the orthorhombic space group Pbca
[a = 9.30318(18) Å, b = 16.8049(3) Å, c = 23.6779(4) Å] (Fig.
Figure 2. Molecular structures of N-alkylated and N-arylated DBC
derivatives.
3d). The DBC unit was determined to have a dihedral angle (C2–
C1–C12–C13) of 16.87(18)º. Furthermore, the 4-nitrophenyl unit
at the nitrogen position led to a distorted structure with a dihedral
angle (C26–C21–N1–C10) of 43.41(14)º. The molecular
orientation was a head-to-tail arrangement of an electron-
donating (D) group, i.e., DBC, and an electron-accepting (A)
group, i.e., the 4-nitrophenyl unit. The intermolecular distance
Next, we synthesized (see ESI for details) N-alkylated and N-
arylated DBC derivatives (Fig. 2), and investigated their thermal,
optical, and electrical properties (Table 3). TGA showed that 3
has high thermal stability: the 10%-weight-loss temperature (T10
of 3 (322 ºC) was higher than that of 2 (269 ºC). The T10 values
of N-(2-ethylhexyl)-DBC (6a, 321 ºC) and N-(3,5-di-tert-
butylphenyl)-DBC (6b, 324 ºC) were almost the same as that of
unsubstituted 3. N-(4-nitrophenyl)-DBC (6c) had a higher T10
value (363 ºC), indicating that DBC derivatives are thermally
stable, which is an advantage in the preparation of thin-film
)
(C2–C26) between the D–A units was 3.4329(14) Å, which is
similar to the sum of the van der Waals radii. These results
suggest that π stacking of 6c is crucial for the formation of a
crystalline structure.
10
devices by vacuum deposition. Differential scanning
calorimetry (DSC) and X-ray diffractometry showed that the
introduction of substituents at the nitrogen atom of DBC resulted
in different morphologies. For compound 3, an endothermic peak
−1
(
m
ΔH: 19 kJ mol ) corresponding to the melting point (T ) was
observed at 159 ºC during the first heating cycle (Fig. 3a). Upon
cooling to room temperature, the compound formed a transparent
glass via a supercooled liquid state. We detected an endothermic
event corresponding to the glass-transition temperature (T ) at 28
g
ºC in the third heating cycle. The formation of a glassy state was
also evident in the X-ray diffraction pattern. After thermal
m
treatment above T , the diffraction pattern showed only a broad
halo, indicating that the DBC unit was amorphous; this is
because of steric hindrance due to the two non-planar
naphthalene rings. The branched alkyl chain in 6a gave rise to a
decrease in T
broad exothermic peak at 78 ºC was identified as the crystalline
temperature (T ), as shown by sharp X-ray reflection peaks.
Finally, the sample showed a T at 113 ºC. Compound 6b, which
contains a di-tert-butylphenyl group, had a higher T . The higher
arises from the rigid phenyl ring bonded to the nitrogen atom.
The N-arylated structure also increases the T (143 ºC) and T
197 ºC) values, affording a thermally stable material.
g g
of −2 ºC. Upon further heating above the T , a
c
m
g
Figure 3. (a) DSC profiles of 3 in (i) first, (ii) second, and (iii) third
heating cycles. Scanning rate: 10 ºC min . (b) Spin-coated films of 3
T
g
−1
c
m
(
i), 6a (ii), and 6b (iii) on fused-silica substrate. (c) Single crystals of
(
6c. (d) Crystal structure of 6c.
Amorphous molecular materials enable the formation of thin
films without grain boundaries, which are suitable for OLEDs.
11
Figure 4a shows the absorption spectra of the DBC derivatives
in 1,4-dioxane. All the spectra indicate clear vibronic structures,
consistent with the rigid structures. Compounds 3, 6a, and 6b
show an absorption peak at around 370 nm, corresponding to the
–0 transition of the DBC unit. In contrast, the 6c spectrum
broadens at around 380 nm, which may be related to the D–A
To explore this molecular function, spin-coated films on fused-
silica substrates were prepared (see ESI). The resulting
amorphous thin films (film thickness: 80 nm) showed good
transparency without light scattering, which is preferable for
solution-processed device fabrication (Fig. 3b).
0
effect between the DBC and nitrophenyl groups. DFT

4
Tetrahedron
calculations show that the nitrophenyl group is involved in
electron localization, resulting from the increased electron-
withdrawing capability of the terminal unit.
spectrometry. We also thank Dr. Mikiko Sodeoka and Dr.
Yoshihiro Sohtome of the Synthetic Organic Chemistry
Laboratory, RIKEN for optical rotation measurements. We thank
Dr. Zhaomin Hou and Dr. Masayoshi Nishiura of the
Organometallic Chemistry Laboratory, RIKEN for DSC and
TGA measurements. We also thank Dr. Keisuke Tajima and Dr.
Kyohei Nakano of the Emergent Functional Polymers Research
Team of RIKEN CEMS for measurements of film thicknesses.
We thank Helen McPherson, PhD, from Edanz Group
12
DBC showed fluorescence in 1,4-dioxane, with a fluorescence
em
maximum (λmax ) at 372 nm, corresponding to a Stokes shift of 7
nm (Fig. 4b). The fluorescence spectra of N-alkylated 6a and N-
em
arylated 6b showed similar λmax values and Stokes shifts. The
small Stokes shifts indicate that the annulated DBC structure is
rigid, suggesting that changes in the molecular shape and size
13
(www.edanzediting.com/ac) for editing a draft of this manuscript.
during photoexcitation are small. Compound 3 gave a
fluorescence quantum yield (Φ ) of 0.66, using quinine sulfate as
a standard. In contrast, 3c showed fluorescence quenching (Φ : <
.001) as a result of charge transfer between the electron-
f
A. Supplementary data
f
0
Electronic Supporting Information (ESI) associated with this
article can be found, in the online version, at
14
localized DBC and 4-nitrophenyl units. Finally, the energy
levels of the DBC derivatives were evaluated using absorption
spectroscopy and photoelectron spectroscopy performed in air
https://doi.org/10.1016/j.tetlet.2017.XX.XX
Contains: Characterization data for all compounds, DSC and
TGA profiles, XRD patterns, DFT calculation, PESA profiles,
and Tauc plots (PDF).
(PESA) (Table 3).
CCDC-1573305 contains the crystallographic data for 6c. The
data can be obtained from The Cambridge Crystallographic Data
Centre (CCDC) via www.ccdc.cam.ac.uk/data_request/cif.
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(
1
(
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15
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1
Acknowledgments
This work was partly supported by JSPS KAKENHI, Grant
Number JP15K05639, for M.K. from the Ministry of Education,
Culture, Sports, Science, and Technology of Japan. We thank the
RIKEN Brain Science Institute for high-resolution mass

5
Highlights
Heterocyclic ring closure of 1,1'-bi-2-naphthol
yields 7H-dibenzo[c,g]carbazole.
7
H-dibenzo[c,g]carbazole is obtained by simple
heating in an autoclave.
Gram-scale synthesis is useful in the development
of optoelectronic materials.