Tandem synthesis of benzo[b]carbazoles and their photoluminescent properties

Article abstract of DOI:10.1002/chem.201301887

5 H-Benzo[b]carbazoles were prepared through a tandem reaction between 2-ethynyl-N-triphenylphosphoranylidene anilines and α-diazoketones through ketenimine intermediates in moderate-to-good yields. By using this approach, benzo[b]benzo[5,6]indolo[3,2-h]carbazoles, fluoreno[9,1-ab]carbazoles, and fluoreno[9,1-ab]fluoreno[1′,9′:5,6,7]indolo[3,2-h]carbazoles were constructed in one pot. Moreover, the resulting products emitted light within the range 410-521a nm, with quantum yields of up to 62 %. Lord of the rings: A series of benzo[b]carbazoles was synthesized through a tandem Wolff-rearrangement/aza-Wittig-reaction/biradical-ketenimine-cyclization/1, 5-H-shift process. The products emitted intense light with high emission quantum yields (see scheme). Copyright

Full text of DOI:10.1002/chem.201301887

FULL PAPER
DOI: 10.1002/chem.201301887
Tandem Synthesis of Benzo[b]carbazoles
and Their Photoluminescent Properties
Yanpeng Xing, Binbin Hu, Qijun Yao, Ping Lu,* and Yanguang Wang*[a]
Abstract: 5H-Benzo[b]carbazoles were prepared through a tandem reaction be-
tween 2-ethynyl-N-triphenylphosphoranylidene anilines and a-diazoketones
through ketenimine intermediates in moderate-to-good yields. By using this ap-
proach, benzo[b]benzo[5,6]indolo[3,2-h]carbazoles, fluoreno[9,1-ab]carbazoles, and
fluoreno[9,1-ab]fluoreno[1’,9’:5,6,7]indolo[3,2-h]carbazoles were constructed in one
Keywords: benzocarbazoles · cycli-
zation · photoluminescence · rear-
rangement · tandem reactions
G
R
G
N
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pot. Moreover, the resulting products emitted light within the range 410–521 nm,
with quantum yields of up to 62%.
Introduction
In the blossoming field of optoelectronics, a large number of
efforts have been made to create new molecules and to opti-
mize their corresponding devices to yield stable working de-
vices with excellent performance.[1] As one type of privi-
leged organic semiconductor, linear fused acenes, such as
pentacene, have been attracting extensive attention, owing
to their unique optical and electronic properties, typically
for application in thin-film organic field-effect transistors
(OFET)s.[2a,b] To enable the fine-tuning of the device param-
eters to afford higher efficiencies, modification of the struc-
turally simple acenes is necessary. One of the useful meth-
ods for such modification is to introduce heteroatoms onto
the backbone to form heteroacenes, of which sulfur[2c] and
nitrogen heteroatoms[2d,e] have received the most attention.
Hybrid nitrogen acenes, termed N-heteroacenes, offer the
benefit of further elaboration for various purposes. For in-
stance, substituted benzo[a]carbazoles have been revealed
to have low-lying LUMOs and might be used as potential n-
type or bipolar organic semiconductors (Figure 1).[3a] Similar
Figure 1. Representative carbazole-based fused heteroacenes.
that could be used to construct various carbocycles and het-
erocycles by trapping with other reagents in a cascade
manner.[4] A large number of methods for the in situ genera-
tion of ketenimines have been reported. One widely used
method to generate ketenimines involves the decomposition
of N-tosyl triazole, which is formed by a copper-catalyzed
alkyne–azide cycloaddition (CuAAC) reaction.[4,5] Further-
more, ketenimines can be also formed through an aza-Wittig
reaction between a ketene and an aza-Wittig reagent.[4,6]
Prompted by the value of N-heteroacenes in the field of
optoelectronics and by our previous investigations on the
thriving chemistry of ketenimines in cascade reactions,[4,6]
we were interested in the synthesis of benzo[b]carbazoles
through ketenimine intermediates. Based on the traditional
retrosynthetic analysis, the four fused rings of benzo[b]car-
bazole are commonly constructed from either substituted in-
doles[7a–c] or substituted naphthalenes,[7d–f] as shown in
Figure 2. Exceptionally, Schmittel et al.[8a] and Shi and
Wang[8b] independently reported a strategy in which three of
the four fused rings of benzo[b]carbazoles could be con-
structed in a single step through a biradical cyclization reac-
tion of the isolated N-(2-alkynylphenyl) ketenimines. Al-
though this reaction offers high bond-formation efficiency,
the diversity of the products is much limited, owing to the
instability of the ketenimines.
properties of carbazolo
ACHTUNGTRENNUNG
served.[3b] Indolo
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lity and high stability.[3c,d] Although a longer extension to
benzo[1,2-b:5,4-b’]dicarbazole and benzo[1,2-b:4,5-b’]dicar-
bazole was achieved through multiple steps, the yields were
low.[3e]
Recently, cascade reactions have been attracting much at-
tention, owing to their high efficiency in forming new bonds.
Ketenimine is a versatile intermediate in organic synthesis
[a] Y. Xing, B. Hu, Q. Yao, Prof. Dr. P. Lu, Prof. Dr. Y. Wang
Department Of Chemistry, Zhejiang University
Hangzhou 310027 (P.R. China)
Fax : (+86)571-87951512
E-mail: pinglu@zju.edu.cn
orgwyg@zju.edu.cn
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201301887.
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Scheme 1. Preparation of compounds 3a–3e: Scope of the reaction with
respect to compounds 2a–2e.
pounds 1a and 2a in a 1:1 molar ratio in 1,2-dichloroethane
(DCE) under a nitrogen atmosphere for 6 h afforded com-
pound 3a in 90% yield.
Figure 2. Synthetic routes to benzo[b]carbazoles.
With the optimized reaction conditions in hand, we tested
the substrate diversity. Firstly, the substituent effects of 2-
Herein, we report a concise strategy for the construction
diazo-1,3-diphenylpropane-1,3-dione
on
the
reaction
of the benzo[b]carbazole skeleton and its extension to
(Scheme 1) were investigated. No apparent electronic effects
were observed. Both electron-donating (such as OCH3) and
electron-withdrawing groups (such as F) on the phenyl rings
of compounds 2a–2e afforded their corresponding products
(3a–3e) in moderate yields.
benzo[b]benzo
carbazole, and fluoreno
[3,2-h]carbazole skeletons (Figure 3), with an illustration of
A
N
ACHTUNGTRENN[UNG 9,1-ab]-
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
their photoluminescence properties.
N-(triphenylphosphoranylidene) anilines 1b–1g also gave
the desired products in good-to-excellent yields (Scheme 2).
Scheme 2. Preparation of compounds 3 f–3k: Scope of the reaction with
respect to compounds 1b–1g.
Figure 3. Carbazole-based skeletons that were synthesized in this work.
Results and Discussion
Notably, 2-diazo-1-phenylbutane-1,3-diones 2 f–2i were
also tolerated in this reaction and furnished their corre-
sponding acetylated benzo[b]carbazoles in 46–64% yield
(Scheme 3).
Because a-diazo-1,3-dicarbonyl compounds, which are typi-
cally prepared through a Regitz diazo-transfer reaction,
could be smoothly transferred into ketenes through a well-
known Wolff rearrangement reaction under thermal condi-
tions,[6] compound 2a was initially selected as the substrate
for the in situ generation of ketenes. The reaction between
compounds 1a and 2a was carried out in toluene under a ni-
trogen atmosphere at 908C for 6 h (Scheme 1). Compound
3a was isolated in 83% yield and its benzo[b]carbazole
structure was confirmed by analogy to the X-ray crystallo-
graphic analysis of its analogue 3i.[9] Delighted by this
result, we optimized the reaction conditions (for detailed
optimization studies, see the Supporting Information,
Table S1). By screening the solvent, reaction temperature,
reaction time, and reaction atmosphere, the optimal reaction
conditions were established. Thus, heating a mixture of com-
However, the reaction of 2-diazo-1,2-diphenylethanone
(4a) with compound 1a did not occur in toluene at 908C
(the starting materials were recovered), thus suggesting that
a higher temperature was required for the Wolff rearrange-
ment of compound 4a. Later, compound 5a was obtained in
85% yield from the reaction between compounds 4a and 1a
at reflux in xylene for 6 h. In this way, analogous compounds
5b–5e were also obtained in moderate yields (Scheme 4).
Above all, benzoyl, acetyl, and phenyl groups were success-
fully installed at the 6-position of benzo[b]carbazole.
When 2-diazo-3-oxo-3-phenylpropanals 6a–6c were ap-
plied to the reaction, the corresponding compounds (7a–7c)
were afforded in relatively lower yields (Scheme 5). In these
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Tandem Synthesis and Photoluminescence of Benzo[b]carbazoles
FULL PAPER
Scheme 6. One-pot preparation of compounds 3 and 7 from azides.
Scheme 3. Preparation of compounds 3l–3q: Scope of the reaction with
respect to compounds 1 and 2 f–2 i.
Scheme 4. Preparation of compounds 5a–5e: Scope of the reaction with
respect to compound 1.
Scheme 7. Proposed mechanism for the formation of benzo[b]carbazoles.
phosphorane A,[10] accompanied by the evolution of nitro-
gen gas. Meanwhile, the Wolff rearrangement of a-diazo
ketone generates ketene B, as expected. With both imino-
phosphorane A and ketene B in solution, a subsequent aza-
Wittig reaction occurs to afford enyne-ketenimine inter-
mediate C. Finally, intermediate C undergoes a biradical
cyclization[8] and a sequential 1,5-H shift to furnish ben-
zo[b]carbazoles.
Scheme 5. Preparation of compounds 7a–7c: Scope of the reaction with
respect to compounds 6a–6c.
cases, the substituent effect was apparent. The presence of
electron-donating groups (such as 4-MeO) on the phenyl
ring of 2-diazo-3-oxo-3-phenylpropanal promoted the reac-
tion and afforded the product in 51% yield, whereas elec-
tron-withdrawing groups (such as 4-Br) did not afford any
detectable product. These results may be attributed to a rel-
atively low stability of the hydrogen-substituted ketenimines
under high temperatures. Thus, various benzo[b]carbazoles
without a substituent at their 6-position were prepared.
More conveniently, iminophosphoranes could be used
without isolation and purification. After the direct treatment
of the azide with triphenylphosphine in a 1:1 molar ratio at
room temperature under a nitrogen atmosphere for 30min,
a-diazo carbonyl was added. The reactions could be per-
formed in one pot and afforded compounds 3a, 3b, 3c, 3l,
and 7c in moderate-to-good yields (Scheme 6).
To achieve more-extended conjugation in the heteroa-
cenes, compound 1i was prepared. On treatment of this
compound with compound 2a at reflux in DCE under a ni-
trogen atmosphere for 6 h,
benzo[b]benzo[5,6]indolo[3,2-h]carbazole (8), was efficiently
constructed in 73% yield. Similarly, when compound 1i was
reacted with compound 4a, benzo[b]benzo[5,6]indolo[3,2-
a brand new backbone,
A
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A
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h]carbazole (9), with four attached phenyl groups, was pro-
duced in 75% yield (Scheme 8).
Notably, 10-diazophenanthren-9ACHTUNTRGNEUNG(10H)-one (4b) could be
prepared and used for the formation of the enyne-keteni-
mine. In these cases, compounds 10 and 11, which contained
a fluorenoACTHNUTRGENUG[N 9,1-ab]carbazole substructure, were synthesized
in 76% and 75% yield, respectively (Scheme 9).
Next, we investigated the photophysical properties of
these benzo[b]carbazoles (Table 1). Compounds 3a–3k ab-
sorbed light within the range 433–444 nm, which was ascri-
bed to the p–p* transition of the benzo[b]carbazole back-
bone. These compounds emitted light within the range 490–
Based on these results, a possible mechanism for this reac-
tion is shown in Scheme 7: Firstly, the Staudinger reaction
between phenyl azide and triphenylphosphine affords imino-
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P. Lu, Y. Wang et al.
5a–5e absorbed light at about 400 nm and emitted light at
about 420 nm (see the Supporting Information, Figure S2).
Without an electron-withdrawing carbonyl group at the 6-
position of the benzo[b]carbazoles, intramolecular charge
transfer was not observed in compounds 5a–5e, which
showed blue-shifted absorptions and emissions. However,
the quantum yields of compounds 5a–5e were significantly
improved to 48.8–62.5%. The quantum yields were about
500-times higher in comparison to those substituted with a
carbonyl groups. Without the phenyl group at the 6-position
of benzo[b]carbazole, compounds 7a and 7b absorbed light
at 392 and 396 nm and emitted light at 410 and 415 nm, re-
spectively (see the Supporting Information, Figure S3).
Compound 7c, which contained a methoxy group at the 9-
position of benzo[b]carbazole, absorbed light at 403 nm and
emitted light at 432 nm; the quantum yields of compounds
7a–7c were within the range 28.7–41.4%. Although com-
pounds 8 and 9 possessed similar backbones, compound 9
emitted light at a shorter wavelength, yet with a much
higher quantum yield (see the Supporting Information, Fig-
ure S4). This phenomenon was similar to the pair of com-
pounds 5 and 3. The molar absorptivities were significantly
increased as the p-conjugation was extended in compounds
10 and 11. Compound 11 absorbed light at a shorter wave-
length, although it possessed a much-larger conjugation
system (see the Supporting Information, Figure S5); com-
pound 11 emitted light at 509 nm, with a larger Stokes shift.
Furthermore, compounds 5, 7, and 9–11 provided a wide
range of maximum emission wavelengths (Figure 4), thus in-
dicating that the emission from this family of compounds
could be color-tunable for multipurpose applications.
Scheme 8. Preparation of compounds 8 and 9.
Scheme 9. Preparation of compounds 10 and 11.
Table 1. Absorption and emission properties of the synthesized com-
pounds.[a]
[b]
Compound
labs [nm] (eꢁ10À3
)
lex [nm]
lem [nm]
F [%][c]
3a
3b
3c
3d
3e
3 f
3g
3h
3i
3j
3k
5a
5b
5c
5d
5e
7a
7b
7c
8
433 (7.2)
439 (6.7)
441 (7.3)
439 (8.3)
444 (8.3)
433 (8.1)
436 (8.8)
434 (8.4)
440 (7.3)
438 (8.4)
435 (7.7)
400 (8.1)
400 (6.8)
406 (7.9)
407 (7.8)
400 (6.4)
392 (5.8)
396 (5.3)
403 (5.7)
445 (7.4)
421 (7.6)
444 (11.2)
436 (30.3)
433
439
441
440
440
433
436
434
440
434
435
400
395
405
407
399
389
393
402
422
412
444
436
507
503
503
494
516
505
508
497
511
490
521
420
422
428
428
420
410
415
432
471
441
471
509
0.05
0.21
0.31
0.17
0.03
0.16
0.13
0.10
0.21
0.10
0.19
50.2
62.5
54.9
51.5
48.8
28.7
32.3
41.4
0.11
48.9
35.0
22.8
9
10
11
Figure 4. Normalized emission spectra of compounds 5a, 7a, and 9–11 in
dilute CH2Cl2.
[a] UV and FL spectra were recorded at a concentration of 1ꢁ10À5 m in
CH2Cl2. [b] In molÀ1 dm3 cmÀ1. [c] Quantum yields were calculated by
using 9,10-diphenylethynylnaphthalene as an external standard.
Conclusion
We have developed a concise and efficient synthesis of ben-
521 nm, with quantum yields of 0.03–0.31% in CH2Cl2 (see
the Supporting Information, Figure S1). Blue-shifted absorp-
tions and emissions were observed for compounds 5a–5e in
comparison with those of compounds 3a–3k. Compounds
zo[b]carbazoles, benzo[b]benzo
fluoreno[9,1-ab]carbazoles,
ab]fluoreno[1’,9’:5,6,7]indolo
reaction involved a tandem Wolff-rearrangement/aza-Wittig-
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ACHTUNGTRENNUNG
A
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AHCTUNGTRENNUNG
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Tandem Synthesis and Photoluminescence of Benzo[b]carbazoles
FULL PAPER
Typical procedure for the synthesis of phenyl(11-phenyl-5H-benzo[b]car-
bazol-6-yl)methanone (3a) in one-pot manner by using an azide as a
starting material: To an oven-dried Schlenk tube that was equipped with
a magnetic stirrer bar were sequentially added 1-azido-2-(phenylethynyl)-
benzene (0.5 mmol), triphenylphosphine (0.5 mmol), and DCE (2 mL)
under a nitrogen atmosphere. The mixture was stirred at RT for 0.5 h.
Then, compound 2a (0.6 mmol, 1.2 equiv) was added to the system and a
condenser was fitted. The reaction mixture was continually stirred at
reflux for 6 h. Upon completion of the reaction, the reaction mixture was
cooled to RT. The solvent was removed under vacuum and the residue
was purified by column chromatography on silica gel (petroleum ether/
EtOAc, 10:1) to give compound 3a (169 mg, 85%) as a yellow solid.
reaction/biradical-cyclization/1,5-H shift process. A variety
of substrates were suitable for this reaction. The products
have been demonstrated to emit light within the range 410–
521 nm, with quantum yields of up to 62% in CH2Cl2. We
believe that these compounds could find applications in op-
toelectronics devices for material science studies or as new
fluorophores for the development of new fluorescent che-
mosensors in the life sciences.
Procedure for the synthesis of (14,16-diphenyl-6,8-dihydrobenzo[b]-
benzoACTHNUTRGENNG[U 5,6]indoloACHTUGNTREN[NUGN 3,2-h]carbazole-5,9-diyl)bis(phenylmethanone) (8): To
Experimental Section
an oven-dried Schlenk tube that was equipped with a magnetic stirrer
bar were sequentially added compound 1i (0.5 mmol), compound 2a
(1.1 mmol, 2.2 equiv), and DCE (3 mL) under a nitrogen atmosphere.
Then, a condenser was fitted and the mixture was heated at reflux for
6 h. Upon completion of the reaction, the solvent was removed under
vacuum and the residue was purified by column chromatography on
silica gel (CH2Cl2) to give compound 8 (262 mg, 73%) as a yellow solid.
Typical procedure for the synthesis of phenyl(11-phenyl-5H-benzo[b]car-
bazol-6-yl)methanone (3a): To an oven-dried Schlenk tube that was
equipped with a magnetic stirrer bar were sequentially added compound
1a (0.5 mmol), compound 2a (0.6 mmol, 1.2 equiv), and DCE (2 mL)
under a nitrogen atmosphere. Then, a condenser was fixed and the mix-
ture was heated at reflux for 6 h. Upon completion of the reaction, the
reaction system was cooled to RT. The solvent was removed under
vacuum and the residue was purified by column chromatography on
silica gel (petroleum ether/EtOAc, 10:1) to give compound 3a (179 mg,
90%) as a yellow solid. M.p. 205–2068C; 1H NMR (500 MHz, CDCl3):
d=9.56 (s, 1H; NH), 7.81 (d, J=7.0 Hz, 2H; CH), 7.76–7.74 (m, 2H;
CH), 7.69–7.64 (m, 3H; CH), 7.58 (t, J=7.3 Hz, 1H; CH), 7.54–7.53 (m,
2H; CH), 7.44 (t, J=7.8 Hz, 2H; CH), 7.38–7.36 (m, 2H; CH), 7.29–7.25
(m, 2H; CH), 6.96–6.93 (m, 1H; CH), 6.83–6.82 ppm (d, J=8.0 Hz, 1H;
CH); 13C NMR (125 MHz, CDCl3): d=198.0, 142.0, 140.7, 140.4, 139.1,
138.3, 132.7, 130.8, 129.8, 129.6, 129.0, 128.6, 128.2, 127.5, 127.0, 125.9,
125.5, 124.1, 123.1, 122.7, 122.6, 119.9, 112.7, 110.5 ppm; IR (neat): n˜ =
3740, 3397, 3059, 1631, 1600, 1464, 1338, 1165, 746, 701 cmÀ1; HRMS
(EI): m/z calcd for C29H19NO: 397.1467; found: 397.1464.
1
M.p.>3008C; H NMR (400 MHz, CDCl3): d=9.54 (s, 2H; NH), 7.80 (d,
J=7.2 Hz, 4H; CH), 7.63 (d, J=8.4 Hz, 2H; CH), 7.59–7.52 (m, 4H;
CH), 7.42 (t, J=7.6 Hz, 4H; CH), 7.36 (t, J=7.8 Hz, 4H; CH), 7.21–7.10
(m, 9H; CH), 7.05–7.01 (t, J=7.6 Hz, 2H; CH), 6.81 ppm (s, 1H; CH);
13C NMR (100 MHz, CDCl3): d=198.4, 142.9, 141.1, 140.2, 137.5, 137.2,
132.8, 129.9, 129.3, 129.0, 128.7, 128.6, 128.1, 126.7, 125.5, 125.0, 123.7,
122.5, 118.0, 116.8, 112.3, 91.5 ppm; IR (neat): n˜ =3673, 1736, 1701, 1620,
1562, 1513, 1459, 1332, 1255, 1140, 755, 697 cmÀ1; HRMS (EI): m/z calcd
for C52H32N2O2: 716.2464; found: 716.2486.
Procedure for the synthesis of 5,9,14,16-tetraphenyl-6,8-dihydrobenzo-
[b]benzoACTHUNTGRENNUG[5,6]indoloAHCTUNGTRENN[GUN 3,2-h]carbazole (9): To an oven-dried Schlenk tube
that was equipped with a magnetic stirrer bar were sequentially added
compound 1i (0.5 mmol), compound 4a (1.1 mmol, 2.2 equiv), and
xylene (2 mL) under a nitrogen atmosphere. Then, a condenser was fitted
and the mixture was heated at reflux for 6 h, during which time, the prod-
uct often precipitated from the reaction system. Upon completion of the
reaction, the mixture was cooled to RT and filtered. The solid was
washed with petroleum ether (3ꢁ5 mL) and dried in vacuum at 408C for
2 h to give compound 9 (248 mg, 75%) as a yellow solid. M.p.>3008C;
1H NMR (500 MHz, [D6]DMSO, 558C): d=10.49 (s, 2H; NH), 7.69–7.65
(m, 6H; CH), 7.58–7.56 (m, 8H; CH), 7.50–7.47 (m, 5H; CH), 7.29–7.22
(m, 9H; CH), 7.16–7.13 ppm (t, J=7.5 Hz, 2H; CH); 13C NMR
(125 MHz, [D6]DMSO, 558C): d=144.0, 137.59, 137.57, 136.4, 130.9,
130.7, 129.4, 129.1, 128.8, 128.7, 128.6, 127.3, 127.1, 125.3, 123.9, 123.4,
122.7, 121.5, 117.1, 116.3, 115.9, 91.3 ppm; IR (neat): n˜ =3461, 2987, 1632,
1442, 1403, 1367, 1312, 1284, 1153, 1073, 753, 698 cmÀ1; HRMS (EI): m/z
calcd for C50H32N2: 660.2565; found: 660.2545.
Typical procedure for the synthesis of 6,11-diphenyl-5H-benzo[b]carba-
zole (5a): To an oven-dried Schlenk tube that was equipped with a mag-
netic stirrer bar were sequentially added compound 1a (0.5 mmol), com-
pound 4a (0.6 mmol, 1.2 equiv), and xylene (2 mL) under a nitrogen at-
mosphere. Then, a condenser was fitted and the mixture was heated at
reflux for 6 h. Upon completion of the reaction, the reaction system was
cooled to RT. The solvent was removed under vacuum and the residue
was purified by column chromatography on silica gel (petroleum ether/
EtOAc, 20:1) to give compound 5a (157 mg, 85%) as a white solid. M.p.
237–2388C; 1H NMR (400 MHz, CDCl3): d=7.86 (d, J=8.8 Hz, 1H;
CH), 7.79–7.77 (m, 2H; NH, CH), 7.63–7.57 (m, 7H; CH), 7.55–7.51 (m,
3H; CH), 7.37 (t, J=7.2 Hz, 1H; CH), 7.29–7.26 (m, 2H; CH), 7.17 (d,
J=8.0 Hz, 1H; CH), 6.88–6.87 ppm (m, 2H; CH); 13C NMR (100 MHz,
CDCl3): d=142.0, 139.1, 137.1, 136.9, 133.4, 130.9, 130.6, 130.2, 129.3,
128.9, 127.84, 127.80, 127.7, 127.0, 126.6, 125.0, 124.4, 123.5, 123.2, 123.0,
122.5, 119.1, 117.6, 109.9 ppm; IR (neat): n˜ =3434, 1671, 1596, 1485, 1392,
1314, 1210, 1161, 1070, 1024, 744, 701 cmÀ1; HRMS (EI): m/z calcd for
C28H19N: 369.1517; found: 369.1518.
Procedure for the synthesis of 8-phenyl-13H-fluorenoACTHUNRTGNEUNG[9,1-ab]carbazole
(10): To an oven-dried Schlenk tube that was equipped with a magnetic
stirrer bar were sequentially added compound 1a (0.5 mmol), compound
4b (0.6 mmol, 1.2 equiv), and xylene (2 mL) under a nitrogen atmos-
phere. Then, a condenser was fitted and the mixture was heated at reflux
for 6 h. Upon completion of the reaction, the solvent was removed under
vacuum and the residue was purified by column chromatography on
silica gel (petroleum ether/EtOAc, 20:1) to give compound 10 (140 mg,
76%) as a yellow solid. M.p. 224–2258C; 1H NMR (400 MHz, CDCl3): d
= 8.32 (brs, 1H; NH), 8.05 (d, J=6.8 Hz, 2H; CH), 7.92 (d, J=7.2 Hz,
1H; CH), 7.70 (d, J=8.0 Hz, 1H; CH), 7.59–7.58 (m, 3H; CH), 7.53–7.49
(m, 3H; CH), 7.45 (t, J=7.2 Hz, 1H; CH), 7.40–7.34 (m, 3H; CH), 7.02
(d, J=8.0 Hz, 1H; CH), 6.85 ppm (t, J=7.4 Hz, 1H; CH); 1H NMR
(400 MHz, [D6]DMSO): d=12.01 (s, 1H; NH), 8.62 (d, J=7.6 Hz, 1H;
CH), 8.30 (dd, 1J=5.6 Hz, 2J=2.4 Hz, 1H; CH), 8.23 (d, J=7.2 Hz, 1H;
CH), 7.74–7.68 (m, 3H; CH), 7.66–7.56 (m, 6H; CH), 7.48–7.44 (m, 2H;
CH), 6.98–6.92 ppm (m, 2H; CH); 13C NMR (100 MHz, CDCl3): d=
142.0, 138.6, 137.9, 137.8, 135.3, 135.1, 134.8, 131.0, 130.3, 128.5, 128.0,
127.02, 126.97, 126.0, 125.8, 125.6, 124.7, 124.5, 123.4, 123.1, 121.7, 120.0,
113.4, 110.5 ppm; IR (neat): n˜ =3436, 2987, 1634, 1611, 1447, 1373, 1313,
Typical procedure for the synthesis of 11-phenyl-5H-benzo[b]carbazole
(7a): To an oven-dried Schlenk tube that was equipped with a magnetic
stirrer bar were sequentially added compound 1a (0.5 mmol), compound
6a (0.6 mmol, 1.2 equiv), and 1,2-dichlorobenzene (2 mL) under a nitro-
gen atmosphere. Then, a condenser was fitted and the mixture was stirred
at 1708C for 2 h. Upon completion of the reaction, the reaction mixture
was cooled to RT and purified directly by column chromatography on
silica gel (petroleum ether/CH2Cl2, 5:1) to give compound 7a (47 mg,
1
32%) as a white solid. M.p. 229–2308C; H NMR (400 MHz, CDCl3): d=
7.91 (d, J=8.4 Hz, 1H; CH), 7.86 (brs, 1H; NH), 7.73–7.69 (m, 2H;
CH), 7.64–7.58 (m, 3H; CH), 7.51–7.44 (m, 3H; CH), 7.38–7.34 (m, 1H;
CH), 7.31–7.28 (m, 2H; CH), 6.93–6.86 ppm (m, 2H; CH); 13C NMR
(100 MHz, CDCl3): d=142.1, 138.9, 133.9, 132.5, 130.1, 128.9, 127.8,
127.5, 127.0, 126.9, 126.3, 125.0, 123.6, 123.3, 123.1, 122.7, 119.1, 109.9,
104.8 ppm; IR (neat): n˜ =3403, 2923, 1628, 1470, 1402, 1343, 1316, 1269,
1146, 1079, 746, 703 cmÀ1; HRMS (EI): m/z calcd for C22H15N: 293.1204;
found: 293.1201.
Chem. Eur. J. 2013, 00, 0 – 0
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P. Lu, Y. Wang et al.
1216, 1104, 1068, 1047, 741, 703 cmÀ1
C28H17N: 367.1361; found: 367.1370.
;
HRMS (EI): m/z calcd for
Montoya, A. Uruvakili, R. A. Orenes, H. Pallamreddy, P. Molina,
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Y. H. Geerts, Org. Lett. 2013, 15, 302–305.
Procedure for the synthesis of 8,10-diphenyl-18,20-dihydrofluoreno
ACHTUNGTNER[NUNG 9,1-
ab]fluoreno[1’,9’:5,6,7]indolo[3,2-h]carbazole (11): To an oven-dried
AHCTUNGTRENNUNG
Schlenk tube that was equipped with a magnetic stirrer bar were sequen-
tially added compound 1i (0.5 mmol), compound 4b (1.1 mmol,
2.2 equiv), and xylene (2 mL) under a nitrogen atmosphere. Then, a con-
denser was fitted and the mixture was heated at reflux for 6 h, during
which time, the product often precipitated from the reaction system.
Upon completion of the reaction, the mixture was cooled to RT and fil-
tered. The solid was washed with petroleum ether (3ꢁ5 mL) and dried
under vacuum at 408C for 2 h to give compound 11 (246 mg, 75%) as a
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1
brown solid. M.p.>3008C; H NMR (400 MHz, [D6]DMSO): d=12.03 (s,
2H; NH), 8.64 (d, J=7.6 Hz, 2H; CH), 8.21 (t, J=6.2 Hz, 4H; CH), 7.83
(s, 1H; CH), 7.66 (t, J=7.4 Hz, 2H; CH), 7.62–7.58 (m, 3H; CH), 7.55–
7.51 (m, 2H; CH), 7.48–7.44 (m, 6H; CH), 7.39 (s, 1H; CH), 7.37–
7.35 ppm (m, 5H; CH); 13C NMR (100 MHz, [D6]DMSO): d=144.0,
137.6, 137.2, 136.1, 135.9, 134.0, 133.5, 129.5, 129.4, 129.2, 128.5, 127.0,
125.6, 125.5, 125.1, 124.3, 124.2, 122.5, 121.7, 119.7, 117.4, 116.7, 111.9,
92.3 ppm; IR (neat): n˜ =3431, 2988, 1623, 1437, 1309, 1232, 1155, 1106,
1044, 751, 700 cmÀ1; HRMS (EI): m/z calcd for C50H28N2: 656.2252;
found: 656.2232.
Acknowledgements
We acknowledge financial support from the National Natural Science
Foundation of China (Nos. 21272204, 21032005, and J1210042).
[9] For ORTEPs of compound 3i, see the Supporting Information.
CCDC-934436 (3i) contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
datarequest/cif.
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Received: May 16, 2013
Published online: && &&, 0000
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Tandem Synthesis and Photoluminescence of Benzo[b]carbazoles
FULL PAPER
Tandem Reactions
Y. Xing, B. Hu, Q. Yao, P. Lu,*
Y. Wang* ...................... &&&& — &&&&
Tandem Synthesis of Benzo[b]carba-
zoles and Their Photoluminescent
Properties
Lord of the rings: A series of ben-
zo[b]carbazoles were synthesized
through a tandem Wolff-rearrange-
ment/aza-Wittig-reaction/biradical-
ketenimine-cyclization/1,5-H-shift
process. The products emitted intense
light with high emission quantum
yields (see scheme).
Chem. Eur. J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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These are not the final page numbers!