Lewis acid mediated one-pot synthesis of aryl/heteroaryl-fused carbazoles involving a cascade Friedel-Crafts alkylation/electrocyclization/aromatization reaction sequence

Article abstract of DOI:10.1002/ejoc.201001309

A Lewis-acid-mediated domino reaction of 2/3-(bromomethyl)indoles with arenes/heteroarenes led to the formation of the corresponding annulated carbazoles. This three-step one-pot transformation proceeds by sequential Lewis acid catalysed Friedel-Crafts alkylation, electrocyclization and aromatization reactions. The strategy is highly efficient for the assembly of complex aryl/heteroaryl-fused carbazoles.

Full text of DOI:10.1002/ejoc.201001309

FULL PAPER
DOI: 10.1002/ejoc.201001309
Lewis Acid Mediated One-Pot Synthesis of Aryl/Heteroaryl-Fused Carbazoles
Involving a Cascade Friedel–Crafts Alkylation/Electrocyclization/Aromatization
Reaction Sequence
Radhakrishnan Sureshbabu,[a] Velu Saravanan,[a] Vasudevan Dhayalan,[a] and
Arasambattu K. Mohanakrishnan*[a]
Keywords: Domino reactions / Friedel–Crafts reactions / Electrocyclization / Annulation / Fused ring systems
A
Lewis-acid-mediated domino reaction of 2/3-(bromo-
catalysed Friedel–Crafts alkylation, electrocyclization and
aromatization reactions. The strategy is highly efficient for
the assembly of complex aryl/heteroaryl-fused carbazoles.
methyl)indoles with arenes/heteroarenes led to the formation
of the corresponding annulated carbazoles. This three-step
one-pot transformation proceeds by sequential Lewis acid
cyclo[a]-fused carbazoles was achieved by the reaction of 2-
aryl/2-heteroarylindole with propargyl alcohol deriva-
tives.[11]
A one-pot synthesis of carbazolonaphthoquinones was
realized in a three-step tandem radical alkylation/cycliza-
tion/aromatization reaction sequence.[12] Very recently,
highly efficient one-pot syntheses of carbazoles and dihy-
drobenzo[a]carbazoles were reported that involve Pd-medi-
ated domino reactions.[13,14]
The synthesis of annulated heterocycles 2 (Scheme 1) by
domino reaction of benzylic bromo compounds 1 contain-
ing a malonylidene unit with arenes and heteroarenes in the
presence of a Lewis acid has been reported by our labora-
tory.[15]
Introduction
Of the indole alkaloids, carbazole is the most explored
due to its prominent biological activity.[1] Several benzo-
and naphthocarbazole analogues have recently been ex-
plored as potential anti-cancer agents.[2] In addition, carb-
azole and its annulated derivatives are often used as func-
tional building blocks in the construction of organic materi-
als for optoelectronic devices due to their unique optical,
electrical and chemical properties.[3] The framework of
benzo[b]carbazoles, being isosteric with that of the antitu-
mor pyrido[4,3-b]carbazole alkaloid, ellipticine, has led to
the development of several approaches to their synthesis.
The most prominent protocols developed for the synthesis
of carbazole analogues involve thermal electrocyclization,[4]
base-mediated cyclization,[5] Diels–Alder reactions[6] and
Pd-mediated cyclization reactions.[7]
Katritzky and co-workers reported the facile synthesis of
hetero-annulated carbazoles by Lewis-acid-mediated dimer-
ization and the intramolecular cyclization of substituted
2/3-(benzotriazol-1-ylmethyl)indole.[8] Saá and co-workers
achieved the synthesis of benz- and hetero-annulated carb-
azoles by Diels–Alder reaction of suitably substituted yn-
amides.[9] Elegant syntheses of indolo[3,2-b]carbazoles[10]
have recently been outlined that involve the iodine-mediated
domino reaction of indole with carbonyl compounds and
also the dimerization of 3-(N,N-dimethylbarbiturylmethyl)-
indole. A novel indium-mediated diverse synthesis of hetero-
Scheme 1. Annulation of benzylic bromide 1.
The main drawback of the methodology is that the dom-
ino reaction sequence involves a cleavage of the carbon–
carbon bond. In addition, the yields of the annulated het-
erocycles 2 obtained are only moderate. As a continuation
of our work on annulated carbazoles,[16] herein we report
our results of the cascade reactions of (bromomethyl)-
indoles with arenes as well as heteroarenes in the presence
of Lewis acids.
[a] Department of Organic Chemistry, University of Madras,
Guindy Campus,
Chennai 600 025, Tamil Nadu, India
Results and Discussion
The required bidentate electrophilic synthons 5a/5b were
prepared in two steps starting from known indolecarbal-
Fax: +91-44-22352494
E-mail: mohan_67@hotmail.com
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201001309.
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Synthesis of Aryl/Heteroaryl-Fused Carbazoles
dehydes 4a/4b[4f] (Scheme 2). Initially, the reactions of Table 1. Annulation of 5a/5b with arenes.[a]
bromo compound 5a with arenes in the presence of a cata-
lytic amount of ZnBr2 or BF3·OEt2 in 1,2-DCE at room
temperature led to the formation of aldehyde 6. However,
the expected domino reactions of 5a/5b with arenes readily
occurred in the presence of 20 mol-% anhydrous FeCl3 in
1,2-DCE at reflux to afford benz-annulated carbazoles 7a–
p in 53–65% yields (Scheme 3).
Scheme 2. Preparation of diacetoxy 2-(bromomethyl)indoles 5a and
5b.
Scheme 3. Cascade reactions of 5a/5b with arenes.
Full details of the nature of the arenes employed and the
yields of the corresponding benzo[b]carbazoles isolated are
given in Table 1. The annulation of bromo compounds 5a/
5b was successfully achieved with a wide variety of arenes.
Surprisingly, the nature of the arenes was found to have
only a minimum influence on the yields of the benzocarb-
azoles (entries 1–3). The presence of the 5-methoxy group
on the benzene portion of the bromo compound 5b was
also found to have only a negligible influence on the annu-
lation yields (entries 2 and 3). The annulation yields of the
[a] Reaction conditions: substrate (0.625 mmol), arene
(0.687 mmol), FeCl3 (0.125 mmol), 1,2-DCE (5 mL), 85 °C, 4 h. [b]
Isolated yields.
Finally, the expected annulation of bromo compounds
benzo[b]carbazoles obtained with bromo compounds 5a/5b 5a/5b with thiophenes/benzo[b]heterocycles was successfully
were better than those obtained with the malonylidene-teth- achieved by using 20 mol-% anhydrous ZnBr2 in 1,2-DCE
ered bromo compounds 1.[15] The structures of annulated at room temperature (Scheme 5) to afford the correspond-
carbazoles 7g and 7m were confirmed by single-crystal X- ing hetero-annulated carbazoles 9a–g in 60–71% yields. As
ray analysis (see Figures 1 and 2).
Next the annulation of bromo compounds 5a/5b was was confirmed by single-crystal X-ray analysis (Figure 3).
planned with heteroarenes. Interaction of bromo compound Next, the annulation protocol was successfully applied to
a representative case, the structure of thienocarbazole 9a
5a with 2-methylthiophene/bithiophene in the presence of the synthesis of complex heterocycles. The reactions of 5a
BF3·OEt2 at room temperature led to the formation of the with 1,3,5-trithienylbenzenes 10a/10b[17] in the presence of
corresponding bis-heteroarylated products 8a/8b in 60 and 20 mol-% anhydrous ZnBr2 in 1,2-DCE at room tempera-
45% yields. Under identical conditions, the reaction of 5a ture led to the formation of the corresponding thienyl
with 1-hexylindole produced di-indolylated 2-(bromo- heterocycles 9h/9i in 69 and 73% yields. However, a similar
methyl)indole 8c in 42% yield (Scheme 4).
reaction of 5a with 1,3,5-trifuranylbenzene 10c[17] failed to
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A. K. Mohanakrishnan et al.
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Figure 1. X-ray crystal structure of compound 7g.
Scheme 5. Annulation of 5a/5b with heteroarenes.
Figure 2. X-ray crystal structure of compound 7m.
Figure 3. X-ray crystal structure of compound 9a.
annulated heterocycle 9m was isolated in 29% yield.
Attempts to perform the annulation of 5a with 9m also
failed to produce bis-annulated heterocycle 9n (Scheme 6).
Next, the reaction of bromo compound 5a with KOAc
in the presence of 18-crown-6 in dry THF led to the forma-
tion of triacetate 13 (Scheme 7). The cascade reactions of
13 with 2-methylthiophene/bithiophene in the presence of
20 mol-% anhydrous FeCl3 led to the isolation of known
Scheme 4. Cascade reactions of 5a with heteroarenes.
produce the expected heterocycle 9j. The reaction of 5a with heterocycles 9a/9b in 56 and 53% yields, respectively. Simi-
thienyl oligomer 10d[17] furnished annulated heterocycle 9k larly, the reaction of 13 with 1-hexylindole afforded
in 60% yield. Under identical conditions, the domino reac- indolo[b]carbazole 9f in 54% yield. Thus, the isolation of
tion of 5a with 4,4-di-p-tolylindeno[1,2-b]thiophene (11)[18] known heterocycles clearly confirms that the initial het-
gave heterocycle 9l in 68% yield. The annulation of 5a with eroarylation of 13 has taken place preferentially on the
1 equiv. of the (9,9-dihexylfluorenyl)thiophene 12[19] fur- benzylic monoacetate rather than the diacetate. However,
nished fluorene-tethered heterocycle 9m in 72% yield. The the reaction of 13 with 2-methylthiophene in the presence
domino reaction of 5a with 0.5 equiv. of 12 failed to pro- of BF3·OEt2 at room temperature led to the isolation of bis-
duce bis-annulated heterocycle 9n; instead, only mono- heteroarylated acetate 14 in 40% yield.
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Synthesis of Aryl/Heteroaryl-Fused Carbazoles
Scheme 6. Annulation of 5a with complex thiophenes.
The isomeric 3-(bromomethyl)indole 15 was prepared in
The domino reaction of 15 was successfully performed
two steps from known 1-(phenylsulfonyl)-3-methylindole-2- with a variety of heteroarenes in the presence of 20 mol-
carbaldehyde.[4f] Similarly to the case of 5a, the annulation % ZnBr2 in 1,2-DCE at room temperature to afford the
of 15 was performed with arenes to afford the correspond- corresponding heterocyclo[b]-fused carbazoles 16e–i in
ing benzo[b]-fused carbazoles in 68–73% yields (Scheme 8). good yields (Scheme 9). Similarly to the arenes, the hetero-
Comparatively, the annulated carbazoles are obtained in cyclo[b]-fused carbazoles were obtained in better yields with
better yields with 3-(bromomethyl)indole 15 than with 2- 3-(bromomethyl)indole 15 than with 2-(bromomethyl)ind-
(bromomethyl)indole 5a.
ole 5a.
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A. K. Mohanakrishnan et al.
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Scheme 7. Cascade reactions of triacetate 13 with heteroarenes.
Scheme 9. Annulation of 3-(bromomethyl)indole 15.
mum yield of the annulation product 7e was obtained by
using InCl3 (entry 5). Surprisingly, annulation proceeded to
give a comparatively low yield using InBr3 (entry 6).
Table 2. Effect of catalyst (20 mol-%) on the cascade reaction of
bromo compound 5a with o-xylene.
Entry
Catalyst
Condition[a]
Yield[b] [%]
1
2
3
4
5
6
7
ZnBr2
ZnBr2
Zn(OTf)2
FeCl3
InCl3
InBr3
r.t.
reflux
reflux
reflux
r.t.
r.t.
r.t.
0[c]
0[c]
0[c]
58
Scheme 8. Annulation of bromo compound 15 with arenes.
62
49
0[c]
Similarly to the malonylidene-tethered bromo com-
pounds 1,[15] the observed annulation may proceed by aryl-
ation followed by elimination of the acetate leading to the
formation of a triene intermediate. The triene intermediate
upon electrocyclization followed by elimination of acetate
and then aromatization may lead to annulation products.
BF3·OEt2
[a] Reaction conditions: substrate (0.625 mmol), o-xylene
(0.687 mmol), FeCl3 (0.125 mmol), 1,2-DCE (5 mL), 85 °C, 4 h. [b]
Isolated yields of 7e. [c] Aldehyde 6 was obtained.
Similarly, the Lewis-acid-mediated annulation of 5a with
The isolation of benzo[b]carbazoles 7a–j in yields almost 2-methylthiophene was performed using 20 mol-% of Lewis
identical to those obtained with arenes having a moderate/ acids and the results obtained are summarized in Table 3.
high electron density certainly rules out the possibility of a The annulation of 5a with 2-methylthiophene was found
Friedel–Crafts-type cyclization.
to be successful with most of the Lewis acids (entries 1–9).
The Lewis-acid-mediated domino reaction of (bro- However, the domino reaction of 5a with 2-methylthio-
momethyl)indole 5a with o-xylene was carried out with phene using Lewis acids such as Sc(OTf)3, Yb(OTf)3 and
20 mol-% of different Lewis acids and the results obtained BF3·OEt2 failed to produce the annulation product 9a, in-
are presented in Table 2. The annulation of 5a with o-xylene stead, only the aldehyde 6 was formed. Comparatively, the
was found to be unsuccessful with zinc salts and BF3·OEt2, annulation of 5a with 2-methylthiophene proceeded to give
affording only aldehyde 6 (entries 1–3 and 7). The maxi- better yields at room temperature. When the annulation of
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Synthesis of Aryl/Heteroaryl-Fused Carbazoles
5a with 2-methylthiophene was performed at reflux in 1,2- ture for 1 h in 1,2-DCE and then at reflux for 4 h, the ex-
DCE, the product 9a was obtained in reduced yields (en- pected annulation products 20a/20b/20c/20d were obtained
tries 4 and 7).
in 63, 76, 57 and 61% yields, respectively.
Table 3. Effect of catalyst (20 mol-%) on the cascade reaction of
bromo compound 5a with 2-methylthiophene.
Entry
Catalyst
Condition[a]
Yield[b] [%]
1
2
3
4
5
6
7
8
AlCl3
ZnCl2
ZnBr2
ZnBr2
FeCl3
InCl3
InCl3
InBr3
Zn(OTf)2
Sc(OTf)3
Yb(OTf)3
BF3·OEt2
r.t.
r.t.
r.t.
reflux
r.t.
r.t.
reflux
r.t.
r.t.
r.t.
r.t.
20
60
71
45
42
79
51
56
62
0[c]
0[c]
0[c]
9
10
11
12
r.t.
[a] Reaction conditions: substrate (0.625 mmol), 2-methylthiophene
(0.687 mmol), ZnBr2 (0.125 mmol), 1,2-DCE (5 mL), room temp.,
4 h. [b] Isolated yields of 9a. [c] Aldehyde 6 was obtained.
Figure 4. X-ray crystal structure of compound 19b.
The reaction of bromo compound 18 with KOAc in dry
The cascade reaction protocol was then studied with THF afforded triacetate 21 in 75% yield. The domino reac-
benzylic bromide 18. In contrast to the 2/3-(bromomethyl)- tions of 21 with 2-methylthiophene, bithiophene, benzo[b]-
indoles 5a/15, 18 reacted with 2-methylthiophene/benzo[b]- thiophene and 1-methylnaphthalene led to the isolation of
thiophene in the presence of 20 mol-% ZnBr2 at room tem- the corresponding annulated products 20a–d in 56, 60, 52
perature for 16 h to give the corresponding bis-heteroaryl- and 52% yields, respectively. Similarly, the domino reac-
ated bromo compounds 19a/19b in 42 and 46% yields tions of 21 with benzo[b]furan, N-pentylindole and (2-eth-
(Scheme 10). The structure of the bis-heteroarylated bromo ylhexyl)carbazole afforded the corresponding annulated
compound 19b was confirmed by a single-crystal X-ray carbazoles 22–24 in 58, 58 and 64% yields, respectively.
analysis (Figure 4). Surprisingly, when the reactions of 18 Note that the heterocycles 22–24 could not be obtained by
with 2-methylthiophene, bithiophene, benzo[b]thiophene the domino reaction of the bromo compound 18
and 1-methylnaphthalene were performed at room tempera- (Scheme 11).
Scheme 10. Cascade reactions of benzyl bromide 18.
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A. K. Mohanakrishnan et al.
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Conclusion
A straightforward and general method for the synthesis
of cyclo[b]-fused carbazoles has been developed starting
from suitably substituted 2/3-(bromomethyl)indoles and ar-
enes under Lewis acid catalysis. The attractive feature of
this protocol is the fact that a wide variety of π-conjugated
annulated carbazoles can be readily accessed by the appro-
priate choice of arenes and heteroarenes. The annulation
protocol has been extended to (bromomethyl)benzene as
well as 2,5-bis(bromomethyl)thiophene. The annulation of
indolyl-2-methylacetate was found to be less suitable than
the corresponding 2-(bromomethyl)indole. However, in the
case of the benzylic system, the corresponding acetate was
found to be more applicable. The Lewis-acid-mediated cas-
cade annulation sequence developed in this work may lead
to new applications in the field of polycyclic aromatic het-
erocycles.
Experimental Section
General Methods: All reactions were carried out in oven-dried ap-
paratus using dry solvent under anhydrous conditions, unless
otherwise noted. Analytical thin-layer chromatography (TLC) was
performed on silica and components were visualized by observa-
tion under iodine or UV light. Flash chromatography was per-
formed by using silica gel (230–400 mesh). IR spectra were re-
corded with a Shimadzu FT-IR 8300 instrument. NMR spectra
(Bruker 300 MHz) were determined in CDCl3 solution containing
TMS as internal standard unless otherwise stated. Organic extracts
were dried with anhydrous Na2SO4. The following abbreviations
denote the multiplicity: s = singlet, d = doublet, t = triplet, q =
quartet, m = multiplet. Chemical shifts (δ) are reported in ppm and
coupling constants (J) in Hz. Carbon types were determined by
13C NMR and DEPT experiments. Elemental analyses were per-
formed with a Perkin–Elmer series II 2400 (IIT Madras) elemental
analyser. Mass spectra were recorded with a JEOL DX 303 HF
mass spectrometer.
Scheme 11. Annulation of benzene triacetate 21.
Finally, the bis-annulation of bromo compound 26[20]
was successfully performed with benzo[b]furan and 2-meth-
ylthiophene to afford heterocycles 27 and 28 in 54 and 50%
yields, respectively (Scheme 12).
5a: Anhydrous InBr3 (0.01 g, 0.030 mmol) was added to a solution
of 2-methyl-1-(phenylsulfonyl)-1H-indole-3-carbaldehyde (1.0 g,
3.34 mmol) in dry acetic anhydride (15 mL). It was then stirred at
room temperature for 4 h under nitrogen. The reaction mixture was
poured onto crushed ice (100 g). The solid obtained was filtered
and washed thoroughly with water and dried. Recrystallization
from methanol afforded pure [2-methyl-1-(phenylsulfonyl)-1H-
indol-3yl]methanediyl diacetate (1.20 g, 90%) as a colourless solid.
Finely powdered NBS (0.49 g, 2.743 mmol) and AIBN (0.05 g)
were added to a solution of [2-methyl-1-(phenylsulfonyl)-1H-indol-
3-yl]methanediyl diacetate (1.0 g, 2.493 mmol) in dry CCl4
(50 mL). The reaction mixture was heated at reflux on a water bath
for 1 h and cooled to room temperature. The floated succinimide
was filtered through Na2SO4 and the solvent was evaporated under
reduced pressure to afford the bromo compound 5a (1.14 g, 85%)
as a colourless solid; m.p. 158–160 °C. 1H NMR (300 MHz,
CDCl3): δ = 8.09 (d, J = 8.1 Hz, 1 H, ArH), 8.02 (s, 1 H, benzylic
CH), 8.00–7.97 (m, 2 H, ArH), 7.84–7.81 (m, 1 H, ArH), 7.61–7.55
(m, 1 H, ArH), 7.49–7.26 (m, 4 H, ArH), 5.28 (s, 2 H, benzylic
CH2), 2.11 (s, 6 H, 2-CH3) ppm. 13C NMR (75.4 MHz, CDCl3): δ
= 168.6, 138.4, 136.3, 135.5, 134.2, 129.3, 127.1, 126.4, 126.2, 124.1,
120.9, 118.1, 114.8, 84.7, 25.1, 20.7 ppm. MS (EI): m/z (%) = 481
Scheme 12. Bis-annulation of tetraacetate 26.
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Synthesis of Aryl/Heteroaryl-Fused Carbazoles
(35) [M]2+, 479 (35) [M]+. C20H18BrNO6S (479.00): calcd. C 50.01,
H 3.78, N 2.92, S 6.68; found C 49.75, H 4.03, N 2.73, S 6.98.
For the single-crystal X-ray analysis of 7g, all calculations were
performed with the SHELXL-97 program.[21] Crystal data for 7g:
C24H17NO4S, MW = 415.43 gmol–1, orthorhombic crystal system,
space group Pbca, Z = 8. a = 13.189(5), b = 16.363(5), c =
5b: The reaction of 4b (1.0 g, 3.039 mmol) with acetic anhydride
(15 mL) in the presence of InBr3 (0.01 g, 0.030 mmol) following the
above procedure afforded [5-methoxy-2-methyl-1-(phenylsulfonyl)-
1H-indol-3-yl]methanediyl diacetate (1.19 g, 91%) as a colourless
solid. The reaction of [5-methoxy-2-methyl-1-(phenylsulfonyl)-1H-
indol-3-yl]methanediyl diacetate (1.0 g, 2.32 mmol) with finely
powdered NBS (0.45 g, 2.552 mmol) and AIBN (0.05 g) in dry
CCl4 using the above procedure afforded compound 5b (1.02 g,
78%) as a colourless solid; m.p. 90–92 °C. 1H NMR (300 MHz,
CDCl3): δ = 8.51 (s, 1 H, benzylic CH), 7.90 (t, J = 7.2 Hz, 3 H,
ArH), 7.60 (s, 1 H, ArH), 7.53 (d, J = 7.5 Hz, 1 H, ArH), 7.42 (t,
J = 7.35 Hz, 2 H, ArH), 6.92 (d, J = 9.3 Hz, 1 H, ArH), 5.30 (s, 2
H, benzylic CH2), 3.76 (s, 3 H, OCH3), 1.99 (s, 6 H, 2-CH3) ppm.
13C NMR (75.4 MHz, CDCl3): δ = 171.1, 156.8, 150.8, 143.6,
136.8, 133.8, 129.4, 128.5, 126.1, 125.8, 115.6, 114.3, 102.2, 95.0,
61.4, 22.2, 19.6 ppm. MS (EI): m/z (%) = 511 (26) [M]2+, 509 (26)
[M]+. C21H20BrNO7S (509.01): calcd. C 49.42, H 3.95, N 2.74, S
6.28; found C 49.23, H 4.18, N 2.48, S 6.57.
18.039(5) Å, α = β = γ = 90(5)°, V = 3893(2) Å3, Dcalcd.
=
1.411 Mgm–3. In total, 19551 independent reflections were col-
lected of which 4813 were considered as observed [IϾ2σ(I)]. The
structure was solved by direct methods and refined by full-matrix
least-squares procedures to give a final R value of 5.24%.
CCDC-776872 contains the supplementary crystallographic data
for 7g. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
8a: BF3·OEt2 (3 drops) was added to a solution of bromo com-
pound 5a (0.30 g, 0.625 mmol) and 2-methylthiophene (0.07 g,
0.687 mmol) in dry 1,2-DCE (5 mL). It was then stirred at room
temperature for 4 h under N2. The reaction mixture was quenched
with ice/water (5 mL), extracted with ethyl acetate (3ϫ10 mL) and
dried (Na2SO4). Removal of the solvent followed by silica gel col-
umn chromatographic purification (hexane/ethyl acetate, 98:2) fur-
nished diarylated bromo compound 8a as a thick brown liquid;
6: ZnBr2 (0.12 mmol) or a catalytic amount of BF3·OEt2 (3 drops)
were added to a solution of bromo compound 5a (0.62 mmol) and
arene (0.68 mmol) in dry 1,2-DCE (5 mL). It was then stirred at
room temperature for 4 h under N2. The reaction mixture was
quenched with ice/water (5 mL), extracted with ethyl acetate
(3ϫ10 mL) and dried (Na2SO4). Removal of the solvent followed
by silica gel column chromatographic purification (hexane/ethyl
acetate, 98:2) furnished aldehyde 6 (0.56 g, 72%) as a colourless
solid; m.p. 112–114 °C. 1H NMR (300 MHz, CDCl3): δ = 10.45 (s,
1 H, CHO), 8.22 (d, J = 7.2 Hz, 1 H, ArH), 8.10 (d, J = 7.5 Hz, 1
H, ArH), 8.04 (d, J = 7.5 Hz, 2 H, ArH), 7.62 (t, J = 7.35 Hz, 1
H, ArH), 7.50 (t, J = 7.8 Hz, 2 H, ArH), 7.40 (td, J = 1.5, J = 1.5,
J = 1.5 Hz, 2 H, ArH), 5.40 (s, 2 H, benzylic CH2) ppm. 13C NMR
(75.4 MHz, CDCl3): δ = 184.8, 143.8, 137.7, 135.8, 134.6, 129.3,
127.0, 126.7, 125.6, 125.3, 121.4, 119.1, 114.2, 19.1 ppm. MS (EI):
m/z (%) = 379 (33) [M]2+, 377 (33) [M]+. C16H12BrNO3S (376.97):
calcd. C 50.81, H 3.20, N 3.70, S 8.48; found C 50.54, H 3.44, N
3.45, S 8.77.
1
yield 0.21 g (60%). H NMR (300 MHz, CDCl3): δ = 8.09 (d, J =
8.1 Hz, 1 H, ArH), 7.85 (d, J = 7.5 Hz, 2 H, ArH), 7.53 (t, J =
7.5 Hz, 1 H, ArH), 7.40 (t, J = 7.65 Hz, 2 H, ArH), 7.28 (t, J =
7.5 Hz, 2 H, ArH), 7.10 (t, J = 7.2 Hz, 1 H, ArH), 6.63 (d, J =
2.7 Hz, 2 H, ArH), 6.53 (dd, J = 1.2, J = 0.9 Hz, 2 H, ArH), 6.02
(s, 1 H, benzylic CH), 5.07 (s, 2 H, benzylic CH2), 2.38 (s, 6 H, 2-
CH3) ppm. 13C NMR (75.4 MHz, CDCl3): δ = 141.9, 139.4, 138.4,
137.2, 134.1, 132.8, 129.3, 128.4, 127.1, 126.8, 126.4, 126.0, 124.8,
123.9, 122.0, 115.2, 38.9, 22.5, 15.4 ppm. MS (EI): m/z (%) = 557
(23) [M]2+, 555 (23) [M]+. C26H22BrNO2S3 (554.99): calcd. C 56.11,
H 3.98, N 2.52, S 17.28; found C 55.83, H 4.23, N 2.28, S 17.51.
8b: The reaction of 5a (0.30 g, 0.625 mmol) with bithiophene
(0.11 g, 0.687 mmol) in dry 1,2-DCE (5 mL) in the presence of
BF3·OEt2 (3 drops) following the same procedure as that used for
8a afforded 8b (0.19 g, 45%) as a thick green liquid. 1H NMR
(300 MHz, CDCl3): δ = 8.13 (d, J = 8.4 Hz, 1 H, ArH), 7.82 (t, J
= 6.75 Hz, 2 H, ArH), 7.41 (t, J = 6.15 Hz, 1 H, ArH), 7.35–7.28
(m, 4 H, ArH), 7.14–7.09 (m, 3 H, ArH), 7.02–7.01 (m, 2 H, ArH),
6.96–6.93 (m, 2 H, ArH), 6.91 (dd, J = 2.1, J = 1.5 Hz, 2 H, ArH),
6.84–6.77 (m, 2 H, ArH), 6.08 (s, 1 H, benzylic CH), 5.09 (s, 2 H,
benzylic CH2) ppm. 13C NMR (75.4 MHz, CDCl3): δ = 143.9,
138.5, 138.2, 135.2, 134.2, 130.7, 130.4, 128.9, 128.5, 128.4, 127.9,
127.2, 125.6, 125.5, 125.1, 124.9, 124.8, 124.3, 122.7, 116.4, 40.0,
20.5 ppm. MS (EI): m/z (%) = 693 (18) [M]2+, 691 (18) [M]+.
C32H22BrNO2S5 (690.94): calcd. C 55.48, H 3.20, N 2.02, S 23.14;
found C 55.22, H 3.42, N 1.83, S 23.42.
General Procedure for the FeCl3-Mediated Domino Reaction of
Bromo Compounds 5a/5b with Arenes: FeCl3 (0.125 mmol) was
added to a solution of bromo compound 5a/5b (0.625 mmol) and
arene (0.687 mmol) in dry 1,2-DCE (5 mL). It was then stirred at
85 °C for 4 h under N2. The reaction mixture was quenched with
ice/water (5 mL), extracted with ethyl acetate (3ϫ10 mL) and dried
(Na2SO4). Removal of the solvent followed by silica gel column
chromatographic purification (hexane/ethyl acetate, 98:2) furnished
the annulation product.
8c: The reaction of 5a (0.30 g, 0.625 mmol) with N-hexylindole
(0.14 g, 0.687 mmol) in dry 1,2-DCE (5 mL) in the presence of
BF3·OEt2 (3 drops) following the same procedure as that used for
8a afforded 8c (0.20 g, 42%) as a thick pink liquid. 1H NMR
(300 MHz, CDCl3): δ = 8.05 (d, J = 8.4 Hz, 1 H, ArH), 7.65 (d, J
7g: The domino reaction of 5a (0.30 g, 0.625 mmol) with benzo-
1,4-dioxane (0.09 g, 0.687 mmol) in dry 1,2-DCE (5 mL) in the
presence of FeCl3 (0.02 g, 0.125 mmol) following the above general
procedure led to the isolation of 7g (0.17 g, 65%) as a colourless
1
solid; m.p. 250–252 °C. H NMR (300 MHz, CDCl3): δ = 8.52 (s, = 7.5 Hz, 2 H, ArH), 7.45 (t, J = 7.5 Hz, 1 H, ArH), 7.31–7.06 (m,
1 H, ArH), 8.29 (d, J = 8.1 Hz, 1 H, ArH), 8.07 (s, 1 H, ArH),
8.03 (d, J = 7.2 Hz, 1 H, ArH), 7.89 (d, J = 7.5 Hz, 1 H, ArH),
8 H, ArH), 7.08 (t, J = 7.5 Hz, 2 H, ArH), 6.90 (t, J = 7.5 Hz, 1
H, ArH), 6.82 (t, J = 7.5 Hz, 2 H, ArH), 6.53 (s, 2 H, ArH), 6.13
7.78 (d, J = 7.2 Hz, 2 H, ArH), 7.53–7.25 (m, 6 H, ArH), 4.35 (s, (s, 1 H, benzylic CH), 4.81 (s, 2 H, benzylic CH2), 3.89 (t, J =
4 H, 2-CH2) ppm. 13C NMR (75.4 MHz, CDCl3): δ = 144.5, 143.7, 6.9 Hz, 3 H, C6H13-H), 1.62 (t, J = 6.45 Hz, 3 H, C6H13-H), 1.17–
139.7, 137.6, 136.4, 133.7, 129.7, 128.9, 128.3, 127.9, 126.9, 126.5,
125.6, 124.2, 120.3, 116.9, 115.4, 112.8, 112.3, 110.7, 64.5,
64.4 ppm. MS (EI): m/z (%) = 415 (61) [M]+. C24H17NO4S (415.08):
calcd. C 69.38, H 4.12, N 3.37, S 7.72; found C 69.08, H 4.38, N
3.15, S 7.99.
1.13 (m, 13 H, C6H13-H), 0.74 (t, J = 6.45 Hz, 7 H, C6H13-H) ppm.
13C NMR (75.4 MHz, CDCl3): δ = 138.4, 137.2, 136.6, 133.6,
132.4, 130.1, 129.0, 128.1, 127.6, 127.3, 126.5, 125.7, 123.8, 121.4,
120.8, 119.7, 118.7, 115.3, 114.4, 109.5, 46.2, 43.5, 31.4, 30.1, 26.5,
23.4, 22.5, 14.0 ppm. MS (EI): m/z (%) = 763 (24) [M]2+, 761 (24)
Eur. J. Org. Chem. 2011, 922–935
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
929

A. K. Mohanakrishnan et al.
FULL PAPER
[M]+. C44H48BrN3O2S (761.26): calcd. C 69.28, H 6.34, N 5.51, S
4.20; found C 69.06, H 6.61, N 5.21, S 4.41.
H, ArH), 7.49 (dd, J = 1.2, J = 0.9 Hz, 1 H, ArH), 7.45–7.42 (m,
2 H, ArH), 7.38 (d, J = 7.5 Hz, 1 H, ArH), 7.29 (d, J = 7.8 Hz, 2
H, ArH), 7.06 (dd, J = 2.4, J = 2.7 Hz, 1 H, ArH), 3.93 (s, 3 H,
OCH3) ppm. 13C NMR (125 MHz, CDCl3): δ = 157.1, 157.0, 156.2,
138.7, 137.4, 133.7, 133.2, 128.9, 127.7, 127.1, 126.5, 123.9, 123.0,
122.9, 121.6, 120.4, 116.4, 114.6, 111.7, 111.0, 103.2, 99.2,
55.8 ppm. C25H17NO4S (427.08): calcd. C 70.24, H 4.01, N 3.28, S
7.50; found C 69.99, H 4.22, N 3.02, S 7.70. HRMS: calcd. for
C25H17NO4S [M]+ 427.0878; found 427.0874.
General Procedure for the ZnBr2-Mediated Domino Reaction of
Bromo Compounds 5a/5b with Heteroarenes: ZnBr2 (0.125 mmol)
was added to a solution of bromo compound 5a/5b (0.625 mmol)
and heteroarene (0.687 mmol) in dry 1,2-DCE (5 mL). It was then
stirred at room temperature for 4 h under N2. The reaction mixture
was quenched with ice/water (5 mL), extracted with ethyl acetate
(3ϫ10 mL) and dried (Na2SO4). Removal of the solvent followed
by silica gel column chromatographic purification (hexane/ethyl
acetate, 98:2) furnished the annulation product.
9e: The domino reaction of 5a (0.30 g, 0.625 mmol) with N-pent-
ylindole (0.13 g, 0.687 mmol) in dry 1,2-DCE (5 mL) in the pres-
ence of ZnBr2 (0.03 g, 0.125 mmol) following the above general
procedure afforded 9e (0.20 g, 70%) as a colourless solid; m.p. 182–
9a: The domino reaction of 5a (0.30 g, 0.625 mmol) with 2-methyl-
thiophene (0.06 g, 0.687 mmol) in dry 1,2-DCE (5 mL) in the pres-
ence of ZnBr2 (0.03 g, 0.125 mmol) following the above general
procedure afforded 9a (0.17 g, 71%) as a colourless solid; m.p. 206–
1
184 °C. H NMR (300 MHz, CDCl3): δ = 9.01 (s, 1 H, ArH), 8.34
(d, J = 8.4 Hz, 1 H, ArH), 8.26 (d, J = 7.8 Hz, 1 H, ArH), 7.94 (d,
J = 7.5 Hz, 1 H, ArH), 7.78 (d, J = 8.1 Hz, 2 H, ArH), 7.71 (s, 1
H, ArH), 7.52–7.17 (m, 8 H, ArH), 4.29 (t, J = 7.2 Hz, 2 H, C5H11-
H), 1.86 (q, J = 7.1 Hz, 2 H, C5H11-H), 1.37 (d, J = 3.6 Hz, 4
H, C5H11-H), 0.86 (t, J = 6.9 Hz, 3 H, C5H11-H) ppm. 13C NMR
(75.4 MHz, CDCl3): δ = 141.6, 139.3, 138.4, 137.5, 133.5, 132.6,
128.8, 127.4, 127.2, 126.5, 126.3, 125.8, 123.9, 123.5, 122.8, 120.6,
119.8, 118.8, 115.7, 108.7, 106.9, 98.5, 43.3, 29.4, 28.6, 22.3,
14.0 ppm. 13C NMR (DEPT 135, 75.4 MHz, CDCl3): δ = 133.5,
128.8, 127.2, 126.5, 126.3, 124.0, 120.6, 119.8, 118.8, 115.7, 108.7,
106.9, 98.5, 43.3, 29.4, 28.6, 22.5, 14.0 ppm. C29H26N2O2S (466.17):
calcd. C 74.65, H 5.62, N 6.00, S 6.87; found C 74.36, H 5.86, N
5.75, S 7.09. HRMS: calcd. for C29H26N2O2S [M]+ 466.1715; found
466.1711.
1
208 °C. H NMR (300 MHz, CDCl3): δ = 8.69 (s, 1 H, ArH), 8.29
(d, J = 8.4 Hz, 1 H, ArH), 8.00 (s, 1 H, ArH), 7.84 (d, J = 7.8 Hz,
1 H, ArH), 7.77 (d, J = 7.5 Hz, 2 H, ArH), 7.47–7.19 (m, 5 H,
ArH), 6.94 (s, 1 H, ArH), 2.57 (s, 3 H, CH3) ppm. 13C NMR
(75.4 MHz, CDCl3): δ = 141.1, 139.7, 138.9, 137.6, 137.4, 135.8,
133.7, 129.0, 127.3, 126.7, 126.4, 124.8, 124.0, 121.0, 119.9, 115.3,
112.9, 108.2, 16.3 ppm. 13C NMR (DEPT 135, 75.4 MHz, CDCl3):
δ = 133.7, 129.0, 127.3, 126.4, 124.1, 121.0, 119.9, 115.3, 112.9,
108.2, 16.3 ppm. C21H15NO2S2 (377.05): calcd. C 66.82, H 4.01, N
3.71, S 16.99; found C 66.57, H 4.25, N 3.42, S 17.25. HRMS:
calcd. for C21H15NO2S2 [M]+ 377.0544; found 377.0549.
For the single-crystal X-ray analysis of 9a, all calculations were
performed with the SHELXL-97 program.[21] Crystal data for 9a:
C21H15NO2S2 (377.46), monoclinic crystal system, space group
P21/C, Z = 4. a = 8.9856(4), b = 10.8157(5), c = 18.3913(9) Å, α =
9f: The domino reaction of 5a (0.30 g, 0.625 mmol) with N-hexyl-
indole (0.14 g, 0.687 mmol) in dry 1,2-DCE (5 mL) in the presence
of ZnBr2 (0.03 g, 0.125 mmol) following the above general pro-
cedure afforded 9f (0.21 g, 69%) as a colourless solid; m.p. 164–
γ
= 90°, β = 101.471(3)°, V = =
1751.67(14) Å3, Dcalcd.
1.431 Mgm–3. In total 30492 independent reflections were collected
of which 4341 were considered as observed [IϾ2σ(I)]. The struc-
ture was solved by direct methods and refined by full-matrix least-
squares procedures to give a final R value of 4.64%.
1
166 °C. H NMR (300 MHz, CDCl3): δ = 8.96 (s, 1 H, ArH), 8.28
(d, J = 8.1 Hz, 1 H, ArH), 8.21 (d, J = 7.5 Hz, 1 H, ArH), 7.90 (d,
J = 7.5 Hz, 1 H, ArH), 7.70 (t, J = 7.05 Hz, 3 H, ArH), 7.42 (d, J
= 8.4 Hz, 2 H, ArH), 7.35–7.30 (m, 3 H, ArH), 7.21–7.15 (m, 3 H,
ArH), 4.26 (t, J = 6.6 Hz, 2 H, C6H13-H), 1.81 (d, J = 6.0 Hz, 2
H, C6H13-H), 1.35–1.18 (m, 6 H, C6H13-H), 0.79 (d, J = 6.3 Hz, 3
H, C6H13-H) ppm. 13C NMR (75.4 MHz, CDCl3): δ = 139.7, 137.5,
136.5, 135.6, 131.6, 130.7, 126.9, 125.5, 125.3, 124.6, 124.4, 123.9,
122.0, 121.6, 121.0, 118.8, 117.9, 116.9, 113.8, 106.7, 105.0, 96.6,
41.4, 29.7, 26.9, 25.1, 20.6, 12.1 ppm. 13C NMR (DEPT 135,
75.4 MHz, CDCl3): δ = 133.5, 128.8, 127.2, 126.5, 126.3, 123.9,
120.7, 119.8, 118.8, 115.7, 108.6, 106.9, 98.5, 43.3, 31.6, 28.8, 27.0,
22.5, 14.0 ppm. 13C NMR (DEPT 90, 75.4 MHz, CDCl3): δ =
133.5, 128.8, 127.2, 126.5, 126.3, 123.9, 120.7, 119.7, 118.8, 115.7,
108.6, 106.9, 98.5 ppm. MS (EI): m/z (%) = 480 (58) [M]+.
C30H28N2O2S (480.18): calcd. C 74.97, H 5.87, N 5.83, S 6.67;
found C 74.75, H 6.13, N 5.56, S 6.92.
CCDC-793489 contains the supplementary crystallographic data
for 9a. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
9c: The domino reaction of 5a (0.30 g, 0.625 mmol) with benzo[b]-
furan (0.08 g, 0.687 mmol) in dry 1,2-DCE (5 mL) in the presence
of ZnBr2 (0.03 g, 0.125 mmol) following the above general pro-
cedure afforded 9c (0.16 g, 66%) as a colourless solid; m.p. 190–
1
192 °C. H NMR (300 MHz, CDCl3): δ = 8.53 (s, 1 H, ArH), 8.34
(t, J = 3.9 Hz, 2 H, ArH), 7.96 (t, J = 6.9 Hz, 2 H, ArH), 7.83 (d,
J = 8.1 Hz, 2 H, ArH), 7.58 (d, J = 8.4 Hz, 1 H, ArH), 7.48–7.25
(m, 7 H, ArH) ppm. 13C NMR (75.4 MHz, CDCl3): δ = 157.0,
156.1, 138.9, 138.0, 137.6, 133.9, 129.1, 127.1, 126.9, 126.5, 126.4,
124.2, 123.8, 122.9, 122.8, 121.6, 120.5, 119.7, 115.2, 111.6, 111.1,
98.9 ppm. 13C NMR (DEPT 90, 75.4 MHz, CDCl3): δ = 133.9,
129.1, 127.1, 126.9, 126.5, 124.2, 122.9, 120.5, 119.7, 115.2, 111.6,
111.1, 98.9 ppm. MS (EI): m/z (%) = 397 (39) [M]+. C24H15NO3S
(397.07): calcd. C 72.53, H 3.80, N 3.52, S 8.07; found C 72.25, H
4.02, N 3.24, S 8.32.
9g: The domino reaction of 5b (0.30 g, 0.588 mmol) with N-hexyl-
indole (0.13 g, 0.647 mmol) in dry 1,2-DCE (5 mL) in the presence
of ZnBr2 (0.03 g, 0.117 mmol) following the above general pro-
cedure afforded 9g (0.20 g, 67%) as a colourless solid; m.p. 174–
1
176 °C. H NMR (300 MHz, CDCl3): δ = 8.99 (s, 1 H, ArH), 8.26
(t, J = 8.85 Hz, 2 H, ArH), 7.72 (d, J = 7.8 Hz, 2 H, ArH), 7.67
(s, 1 H, ArH), 7.51 (t, J = 7.5 Hz, 1 H, ArH), 7.41 (d, J = 6.6 Hz,
2 H, ArH), 7.35–7.17 (m, 4 H, ArH), 7.06 (d, J = 9.0 Hz, 1 H,
ArH), 4.33 (t, J = 7.2 Hz, 2 H, C6H13-H), 3.93 (s, 3 H, OCH3),
1.90 (t, J = 6.9 Hz, 2 H, C6H13-H), 1.43–1.25 (m, 6 H, C6H13-H),
0.87 (d, J = 6.6 Hz, 3 H, C6H13-H) ppm. 13C NMR (125 MHz,
CDCl3): δ = 157.0, 141.7, 138.4, 137.2, 133.7, 133.3 (2 C), 128.7,
128.6, 126.5, 126.3, 126.1, 123.6, 122.9, 120.7, 118.8, 116.9, 114.9,
9d: The domino reaction of 5b (0.30 g, 0.588 mmol) with benzo[b]-
furan (0.07 g, 0.647 mmol) in dry 1,2-DCE (5 mL) in the presence
of ZnBr2 (0.03 g, 0.117 mmol) following the above general pro-
cedure afforded 9d (0.16 g, 63%) as a colourless solid; m.p. 198–
1
200 °C. H NMR (300 MHz, CDCl3): δ = 8.51 (s, 1 H, ArH), 8.33
(s, 1 H, ArH), 8.24 (d, J = 9.0 Hz, 1 H, ArH), 7.99 (d, J = 7.5 Hz,
1 H, ArH), 7.78 (d, J = 7.5 Hz, 2 H, ArH), 7.60 (d, J = 8.1 Hz, 1
930
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 922–935

Synthesis of Aryl/Heteroaryl-Fused Carbazoles
108.6, 107.3, 103.2, 98.4, 55.8, 43.3, 31.6, 28.8, 27.0, 22.5,
14.0 ppm. C31H30N2O3S (510.19): calcd. C 72.91, H 5.92, N 5.49,
S 6.28; found C 72.63, H 6.13, N 5.24, S 6.57. HRMS: calcd. for
C31H30N2O3S [M]+ 510.1977; found 510.1979.
lowing the above general procedure afforded 9l (0.26 g, 68%) as a
colourless solid; m.p. 286–288 °C. H NMR (500 MHz, CDCl3): δ
1
= 8.83 (s, 1 H, ArH), 8.27 (d, J = 8.5 Hz, 1 H, ArH), 7.94 (s, 1 H,
ArH), 7.84–7.80 (m, 3 H, ArH), 7.55 (d, J = 10.0 Hz, 1 H, ArH),
7.46–7.43 (m, 3 H, ArH), 7.36–7.30 (m, 4 H, ArH), 7.23–7.18 (m,
4 H, ArH), 7.02 (d, J = 5.0 Hz, 5 H, ArH), 2.25 (s, 6 H, 2-
CH3) ppm. 13C NMR (125 MHz, CDCl3): δ = 156.4, 147.5, 144.3,
142.0, 139.9, 138.9, 137.8, 137.3, 136.6, 135.7, 133.8, 131.1, 129.1
(2 C), 128.3, 127.5, 126.8, 126.5, 126.4, 125.2, 123.8, 120.1, 119.8,
115.0, 112.6, 110.0, 63.9, 20.9 ppm. 13C NMR (DEPT 135,
125 MHz, CDCl3): δ = 133.8, 129.1 (2 C), 128.3, 127.5, 126.8,
126.5, 125.0, 123.8, 120.1, 119.8, 115.0, 112.6, 110.0, 20.9 ppm.
HRMS: calcd. for C41H29NO2S2 [M]+ 631.1640; found 631.1643.
9h: The domino reaction of 5a (0.3 g, 0.625 mmol) with 2-[3,5-bis-
(thiophen-2-yl)phenyl]thiophene (10a; 0.22 g, 0.687 mmol) in dry
1,2-DCE (5 mL) in the presence of ZnBr2 (0.03 g, 0.125 mmol) fol-
lowing the above general procedure afforded 9h (0.25 g, 69%) as a
1
colourless solid; m.p. 128–130 °C. H NMR (300 MHz, CDCl3): δ
= 8.70 (s, 1 H, ArH), 8.22 (d, J = 7.8 Hz, 1 H, ArH), 8.09 (s, 1 H,
ArH), 7.81 (d, J = 6.9 Hz, 1 H, ArH), 7.71 (t, J = 10.3 Hz, 5 H,
ArH), 7.54 (s, 1 H, ArH), 7.33 (s, 4 H, ArH), 7.26–7.21 (m, 5 H,
ArH), 7.04 (s, 2 H, ArH) ppm. 13C NMR (75.4 MHz, CDCl3): δ =
143.3 (2 C), 139.4, 139.0, 137.6, 137.4, 136.5, 135.7, 135.6, 135.4,
133.9, 129.1, 128.2, 127.6, 126.5, 125.5, 125.4, 124.1, 124.0, 123.4,
122.9, 120.0, 119.6, 115.3, 114.2, 108.3 ppm. 13C NMR (DEPT 90,
75.4 MHz, CDCl3): δ = 133.9, 129.1, 128.2, 127.6, 126.5, 125.5,
124.2, 124.0, 123.3, 122.9, 120.0, 119.6, 115.3, 114.2, 108.3 ppm.
MS (EI): m/z (%) = 603 (26) [M]+. C34H21NO2S4 (603.04): calcd.
C 67.63, H 3.51, N 2.32, S 21.24; found C 67.91, H 3.27, N 2.51,
S 21.02.
9m: The domino reaction of 5a (0.30 g, 0.625 mmol) with 2-[9,9-
dihexyl-2-(thiophen-2-yl)-9H-fluoren-7-yl]thiophene (12; 0.34 g,
0.687 mmol) in dry 1,2-DCE (5 mL) in the presence of ZnBr2
(0.03 g, 0.125 mmol) following the above general procedure af-
forded 9m (0.35 g, 72%) as a pale-yellow solid; m.p. 108–110 °C.
1H NMR (300 MHz, CDCl3): δ = 8.73 (s, 1 H, ArH), 8.25 (d, J =
7.8 Hz, 1 H, ArH), 8.12 (s, 1 H, ArH), 7.84 (d, J = 6.6 Hz, 1 H,
ArH), 7.74 (d, J = 7.2 Hz, 2 H, ArH), 7.62–7.58 (m, 5 H, ArH),
7.52 (d, J = 6.0 Hz, 2 H, ArH), 7.31 (s, 3 H, ArH), 7.21 (s, 4 H,
ArH), 7.03 (s, 1 H, ArH), 1.97 (s, 4 H, C6H13-H), 1.17 (s, 3 H,
C6H13-H), 0.98 (s, 10 H, C6H13-H), 0.67 (s, 9 H, C6H13-H) ppm.
13C NMR (75.4 MHz, CDCl3): δ = 150.7, 144.0 (2 C), 140.1, 138.9,
138.3, 138.0, 136.7, 136.5, 135.3, 132.8, 132.5, 131.8, 128.0, 127.0,
126.5, 125.5, 125.4, 124.5, 124.3, 124.0, 123.6, 123.1, 121.9, 119.5,
119.2, 119.1 (2 C), 118.9, 117.5, 114.3, 112.8, 107.4, 54.3, 39.4,
30.4, 28.6, 22.7, 21.5, 12.9 ppm. 13C NMR (DEPT 135, 75.4 MHz,
CDCl3): δ = 133.8, 129.0, 128.1, 127.6, 126.5, 125.5, 125.0, 124.6,
124.2, 123.0, 120.6, 120.3, 120.2, 120.1, 120.0, 118.5, 115.4, 113.8,
108.4, 40.7, 31.4, 29.7, 23.8, 22.6, 14.0 ppm. 13C NMR (DEPT 90,
75.4 MHz, CDCl3): δ = 132.8, 128.0, 127.0, 126.5, 125.4, 124.5,
124.0, 123.6, 123.1, 121.9, 119.5, 119.2, 119.1 (2 C), 118.9, 117.4,
114.3, 112.8, 107.3, 39.4, 30.4, 28.6, 22.7, 21.5, 12.9 ppm. HRMS:
calcd. for C49H47NO2S3 [M]+ 777.2769; found 777.2765.
9i: The domino reaction of 5a (0.30 g, 0.625 mmol) with 2-[3,5-
bis(3-methylthiophen-2-yl)phenyl]-3-methylthiophene (10b; 0.25 g,
0.687 mmol) in dry 1,2-DCE (5 mL) in the presence of ZnBr2
(0.03 g, 0.125 mmol) following the above general procedure af-
1
forded 9i (0.29 g, 73%) as a colourless solid; m.p. 208–210 °C. H
NMR (500 MHz, CDCl3): δ = 8.81 (s, 1 H, ArH), 8.34 (d, J =
5.0 Hz, 1 H, ArH), 8.20 (s, 1 H, ArH), 8.01 (d, J = 10.0 Hz, 1 H,
ArH), 7.82 (d, J = 10.0 Hz, 2 H, ArH), 7.62 (d, J = 5 Hz, 2 H,
ArH), 7.59 (d, J = 5 Hz, 1 H, ArH), 7.51 (t, J = 7.5 Hz, 1 H, ArH),
7.45–7.38 (m, 2 H, ArH), 7.30 (t, J = 7.5 Hz, 2 H, ArH), 7.26 (d,
J = 5 Hz, 2 H, ArH), 6.98 (d, J = 5 Hz, 2 H, ArH), 2.62 (s, 3 H,
CH3), 2.44 (s, 6 H, 2-CH3) ppm. 13C NMR (125 MHz, CDCl3): δ
= 139.0, 138.9, 138.3, 137.6, 136.9, 135.5, 135.1, 133.8 (2 C), 131.3,
129.0, 128.9, 128.7, 127.5, 127.4, 126.7, 126.5, 125.0, 124.1, 123.9,
119.9, 115.4, 112.7, 108.3, 15.1, 13.0 ppm. 13C NMR (DEPT 135,
125 MHz, CDCl3): δ = 133.8, 131.3, 129.0, 128.9, 128.7, 127.5,
126.5, 124.1, 123.9, 119.9, 115.4, 112.7, 108.3, 15.1, 13.1 ppm. MS
(EI): m/z (%) = 645 (16) [M]+. C37H27NO2S4 (645.09): calcd. C
68.81, H 4.21, N 2.17, S 19.86; found C 68.53, H 4.02, N 1.98, S
20.09.
13: Potassium acetate (0.41 g, 4.166 mmol) and 18-crown-6 (0.05 g,
0.208 mmol) were added to a solution of bromo compound 5a
(1.0 g, 2.083 mmol) in dry THF (20 mL). The mixture was then
stirred at room temperature under nitrogen for 4 h. The solvent
was removed and the residue was extracted with ethyl acetate
(2ϫ20 mL) and dried (Na2SO4). Removal of the solvent followed
by column chromatographic purification (hexane/ethyl acetate,
98:2) led to the isolation of triacetate 13 (0.75 g, 78%) as a colour-
less solid; m.p. 132–134 °C. 1H NMR (300 MHz, CDCl3): δ = 8.18
(d, J = 8.4 Hz, 1 H, ArH), 8.09 (s, 1 H, benzylic CH), 7.92 (d, J =
7.5 Hz, 2 H, ArH), 7.88 (d, J = 7.5 Hz, 1 H, ArH), 7.57 (t, J =
7.35 Hz, 1 H, ArH), 7.48–7.38 (m, 3 H, ArH), 7.32 (t, J = 7.5 Hz,
1 H, ArH), 5.71 (s, 2 H, benzylic CH2), 2.07 (s, 6 H, 2-CH3), 1.96
(s, 3 H, CH3) ppm. 13C NMR (75.4 MHz, CDCl3): δ = 170.1, 168.5,
138.8, 136.5, 134.1, 133.1, 129.5, 129.3, 126.8, 126.1, 124.0, 121.3,
119.1, 114.7, 85.4, 55.8, 20.7 ppm. MS (EI): m/z (%) = 459 (67)
[M]+. C22H21NO8S (459.09): calcd. C 57.51, H 4.61, N 3.05, S 6.98;
found C 57.23, H 4.84, N 2.83, S 7.23.
9k: The domino reaction of 5a (0.30 g, 0.625 mmol) with 2-{3,5-
bis[5-(thiophen-2-yl)thiophen-2-yl]phenyl}-5-(thiophen-2-yl)thio-
phene (10d; 0.40 g, 0.687 mmol) in dry 1,2-DCE (5 mL) in the pres-
ence of ZnBr2 (0.03 g, 0.125 mmol) following the above general
procedure afforded 9k (0.32 g, 60%) as a pale-yellow solid; m.p.
1
246–248 °C. H NMR (300 MHz, CDCl3): δ = 8.68 (s, 1 H, ArH),
8.25 (d, J = 8.4 Hz, 1 H, ArH), 8.11 (s, 1 H, ArH), 7.87 (d, J =
7.5 Hz, 1 H, ArH), 7.75 (d, J = 7.2 Hz, 2 H, ArH), 7.43 (t, J =
7.2 Hz, 2 H, ArH), 7.41–7.31 (m, 4 H, ArH), 7.28–7.22 (m, 4 H,
ArH), 7.19–7.15 (m, 9 H, ArH), 7.07 (d, J = 3.9 Hz, 1 H, ArH),
7.00–6.97 (m, 1 H, ArH) ppm. 13C NMR (75.4 MHz, CDCl3): δ =
138.0, 136.5, 136.2, 136.0, 135.8, 135.5, 132.8, 128.0, 126.9, 126.6,
125.4, 124.8, 123.8, 123.4, 123.1, 123.0, 119.0, 117.9, 115.7, 114.3,
112.8, 107.2 ppm. 13C NMR (DEPT 90, 75.4 MHz, CDCl3): δ =
133.8, 129.1 (2 C), 127.9, 127.6, 126.5 (2 C), 125.8, 124.9, 124.4,
124.2, 124.0, 120.0, 118.9, 115.3, 113.8, 108.3 ppm. MS (EI): m/z
(%) = 850 (54) [M]+. C46H27NO2S7 (849.00): calcd. C 64.99, H 3.20,
N 1.65, S 26.40; found C 65.21, H 2.92, N 1.86, S 26.13.
14: BF3·OEt2 (3 drops) was added to a solution of triacetate 13
(0.30 g, 0.653 mmol) and 2-methylthiophene (0.07 g, 0.718 mmol)
in dry 1,2-DCE (5 mL). The mixture was then stirred at room tem-
perature for 4 h under N2. The reaction mixture was quenched with
ice/water (5 mL), extracted with ethyl acetate (3ϫ10 mL) and dried
(Na2SO4). Removal of the solvent followed by silica gel column
chromatographic purification (hexane/ethyl acetate, 98:2) furnished
diarylated compound 14 (0.14 g, 40%) as thick brown liquid. 1H
9l: The domino reaction of 5a (0.30 g, 0.625 mmol) with 4,4-di-p-
tolyl-4H-indeno[1,2-b]thiophene (11; 0.24 g, 0.687 mmol) in dry
1,2-DCE (5 mL) in the presence of ZnBr2 (0.03 g, 0.125 mmol) fol-
Eur. J. Org. Chem. 2011, 922–935
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
931

A. K. Mohanakrishnan et al.
FULL PAPER
NMR (300 MHz, CDCl3): δ = 8.34 (d, J = 7.5 Hz, 1 H, ArH), 8.17 133.8, 129.0, 127.7, 127.6, 126.4, 124.2, 122.8, 120.9, 120.1, 115.5,
(d, J = 8.1 Hz, 1 H, ArH), 7.96 (d, J = 7.8 Hz, 2 H, ArH), 7.78 (d, 111.7, 107.0, 102.1 ppm. HRMS: calcd. for C24H15NO3S [M]+
J = 7.5 Hz, 1 H, ArH), 7.61 (t, J = 7.5 Hz, 1 H, ArH), 7.49 (t, J
= 7.65 Hz, 1 H, ArH), 7.44–7.38 (m, 2 H, ArH), 7.24 (t, J =
7.95 Hz, 1 H, ArH), 7.19–7.06 (m, 1 H, ArH), 6.59 (d, J = 3.3 Hz,
1 H, ArH), 6.52 (d, J = 3 Hz, 1 H, ArH), 6.07 (s, 1 H, benzylic
CH), 5.52 (s, 2 H, benzylic CH2), 2.37 (s, 6 H, 2-Me), 1.94 (s, 3 H,
CH3) ppm. 13C NMR (75.4 MHz, CDCl3): δ = 169.9, 142.9, 139.0,
138.6, 138.5, 134.7, 129.5, 128.9, 127.0, 126.9, 126.4, 126.0, 125.5,
125.4, 124.5, 122.5, 114.3, 54.8, 39.1, 20.7, 15.4 ppm. MS (EI): m/z
(%) = 535 (17) [M]+. C28H25NO4S3 (535.09): calcd. C 62.78, H 4.70,
N 2.61, S 17.96; found C 63.07, H 4.46, N 2.82, S 17.78.
397.0773; found 397.0778.
16g: The domino reaction of 15 (0.3 g, 0.625 mmol) with N-hexyl-
indole (0.14 g, 0.687 mmol) in dry 1,2-DCE (5 mL) in the presence
of ZnBr2 (0.03 g, 0.125 mmol) following the above general pro-
cedure for heteroarenes afforded 16g (0.23 g, 78%) as a colourless
1
solid; m.p. 262–264 °C. H NMR (300 MHz, CDCl3): δ = 8.51 (s,
1 H, ArH), 8.33 (d, J = 6.6 Hz, 2 H, ArH), 8.14 (d, J = 7.5 Hz, 1
H, ArH), 7.96 (d, J = 7.2 Hz, 1 H, ArH), 7.78 (d, J = 7.2 Hz, 2 H,
ArH), 7.51–7.34 (m, 5 H, ArH), 7.28–7.23 (m, 3 H, ArH), 4.42 (t,
J = 7.2 Hz, 2 H, C6H13-H), 1.95 (quint., J = 7.27 Hz, 2 H, C6H13-
H), 1.51–1.28 (m, 6 H, C6H13-H), 0.88 (t, J = 7.05 Hz, 3 H, C6H13-
H) ppm. 13C NMR (125 MHz, CDCl3): δ = 141.4, 140.9, 138.7,
137.9, 137.7, 133.6, 128.9, 127.6, 126.4, 126.0, 125.8, 124.1, 122.5,
120.9, 120.1, 119.9, 119.2, 119.1, 115.4, 111.1, 108.7, 95.2, 43.3,
31.7, 28.8, 27.0, 22.5, 14.0 ppm. 13C NMR (DEPT 135, 125 MHz,
CDCl3): δ = 133.7, 128.9, 126.4, 126.0, 125.8, 124.2, 120.1, 119.2,
119.1, 115.4, 111.1, 108.7, 95.2, 43.3, 31.7, 28.8, 27.0, 22.5,
14.0 ppm. HRMS: calcd. for C30H28N2O2S [M]+ 480.1871; found
480.1877.
15: The reaction of 3-methyl-1-(phenylsulfonyl)-1H-indole-2-carb-
aldehyde (1.0 g, 3.34 mmol) with acetic anhydride (15 mL) in the
presence of InBr3 (0.01 g, 0.030 mmol) following the same pro-
cedure as that used for 5a afforded [3-methyl-1-(phenylsulfonyl)-
1H-indol-2-yl]methanediyl diacetate (1.18 g, 88%) as a colourless
solid. The reaction of [3-methyl-1-(phenylsulfonyl)-1H-indol-2-yl]-
methanediyl diacetate (1.0 g, 2.493 mmol) with finely powdered
NBS (0.49 g, 2.743 mmol) and AIBN (0.05 g) in dry CCl4 (50 mL)
following the same procedure as that used for 5a afforded com-
1
pound 15 (1.09 g, 92%) as a colourless solid; m.p. 128–130 °C. H
16h: The domino reaction of 15 (0.3 g, 0.625 mmol) with 4,4-di-p-
tolyl-4H-indeno[1,2-b]thiophene (11; 0.24 g, 0.687 mmol) in dry
1,2-DCE (5 mL) in the presence of ZnBr2 (0.03 g, 0.125 mmol) fol-
lowing the above general procedure for heteroarenes afforded 16h
(0.29 g, 74%) as a colourless solid; m.p. 182–184 °C. 1H NMR
(300 MHz, CDCl3): δ = 8.49 (s, 1 H, ArH), 8.33 (d, J = 8.1 Hz, 1
H, ArH), 8.29 (s, 1 H, ArH), 7.87 (d, J = 7.8 Hz, 1 H, ArH), 7.55–
7.47 (m, 6 H, ArH), 7.35 (t, J = 7.5 Hz, 4 H, ArH), 7.28 (s, 3 H,
ArH), 7.13–7.11 (m, 6 H, ArH), 2.32 (s, 6 H, 2-CH3) ppm. 13C
NMR (125 MHz, CDCl3): δ = 156.8, 148.3, 143.2, 140.6, 139.8,
139.3, 137.3, 137.1, 136.6, 136.5, 133.7, 133.5, 129.2, 128.7, 128.5,
127.5 (2 C), 127.1, 126.5, 126.2, 125.3, 124.4, 124.2, 119.9, 119.8,
115.5, 114.7, 108.4, 63.8, 21.0 ppm. 13C NMR (DEPT 135,
125 MHz, CDCl3): δ = 133.6, 129.2, 128.7, 128.5, 127.5 (2 C),
127.1, 126.5, 125.2, 124.2, 119.9, 119.8, 115.5, 114.7, 108.4,
21.0 ppm. MS (EI): m/z (%) = 631 (42) [M]+. C41H29NO2S2
NMR (300 MHz, CDCl3): δ = 8.50 (s, 1 H, benzylic CH), 8.10 (d,
J = 8.1 Hz, 1 H, ArH), 8.01 (d, J = 7.5 Hz, 2 H, ArH), 7.65 (d, J
= 7.5 Hz, 1 H, ArH), 7.58 (t, J = 7.35 Hz, 1 H, ArH), 7.48 (t, J =
7.5 Hz, 2 H, ArH), 7.43–7.31 (m, 2 H, ArH), 4.87 (s, 2 H, benzylic
CH2), 2.19 (s, 6 H, 2-CH3) ppm. 13C NMR (75.4 MHz, CDCl3): δ
= 168.2, 138.1, 136.0, 134.3, 130.8, 129.3, 127.9, 127.1, 126.6, 124.0,
121.1, 119.5, 114.8, 84.6, 22.6, 20.8 ppm. MS (EI): m/z (%) = 481
(29) [M]2+, 479 (29) [M]+. C20H18BrNO6S (479.00): calcd. C 50.01,
H 3.78, N 2.92, S 6.68; found C 49.78, H 3.99, N 2.66, S 6.98.
16d: The domino reaction of 15 (0.3 g, 0.625 mmol) with 1-methyl-
naphthalene (0.10 g, 0.687 mmol) in dry 1,2-DCE (5 mL) in the
presence of FeCl3 (0.02 g, 0.125 mmol) following the above general
procedure for arenes led to the isolation of 16d (0.18 g, 71%) as a
1
colourless solid; m.p. 210–212 °C. H NMR (300 MHz, CDCl3): δ
= 9.09 (s, 1 H, ArH), 8.78 (d, J = 8.1 Hz, 1 H, ArH), 8.67 (s, 1 H,
ArH), 8.35 (d, J = 8.1 Hz, 1 H, ArH), 8.06 (t, J = 7.05 Hz, 2 H, (631.16): calcd. C 77.94, H 4.63, N 2.22, S 10.15; found C 77.66,
ArH), 7.84 (d, J = 7.5 Hz, 2 H, ArH), 7.75 (s, 1 H, ArH), 7.67 (td, H 4.91, N 2.03, S 10.35.
J = 1.2, J = 0.9, J = 1.2 Hz, 2 H, ArH), 7.55–7.50 (m, 1 H, ArH),
16i: The domino reaction of 15 (0.3 g, 0.625 mmol) with 2-[9,9-
7.40 (q, J = 6.9 Hz, 2 H, ArH), 7.29–7.24 (m, 2 H, ArH), 2.76 (s,
dihexyl-2-(thiophen-2-yl)-9H-fluoren-7-yl]thiophene (12; 0.34 g,
3 H, CH3) ppm. 13C NMR (125 MHz, CDCl3): δ = 139.5, 137.7,
0.687 mmol) in dry 1,2-DCE (5 mL) in the presence of ZnBr2
137.5, 133.7, 132.9, 131.9, 131.7, 130.3, 129.0, 127.8, 127.3, 126.8,
(0.03 g, 0.125 mmol) following the above general procedure for het-
126.5 (2 C), 126.4, 125.7, 124.8, 124.2, 122.8, 120.2, 115.3, 113.5,
eroarenes afforded 16i (0.37 g, 78%) as a pale-yellow solid; m.p.
132–134 °C. H NMR (300 MHz, CDCl3): δ = 8.18 (s, 1 H, ArH),
8.33 (d, J = 8.1 Hz, 1 H, ArH), 8.24 (s, 1 H, ArH), 7.96 (d, J =
7.5 Hz, 1 H, ArH), 7.82 (d, J = 7.8 Hz, 2 H, ArH), 7.74–7.68 (m,
5 H, ArH), 7.64–7.59 (m, 2 H, ArH), 7.51 (t, J = 7.8 Hz, 1 H,
ArH), 7.44–7.39 (m, 3 H, ArH), 7.33–7.30 (m, 3 H, ArH), 7.13 (d,
J = 3.6 Hz, 1 H, ArH), 2.08 (d, J = 5.1 Hz, 4 H, C6H13-H), 1.67
112.6, 20.1 ppm. 13C NMR (DEPT 135, 125 MHz, CDCl3): δ =
133.7, 129.0, 128.1, 127.3, 126.5 (2 C), 126.4, 124.8, 124.2, 122.8,
120.2, 115.3, 113.5, 112.6, 20.1 ppm. C27H19NO2S (421.11): calcd.
1
C 76.93, H 4.54, N 3.32, S 7.61; found C 77.21, H 4.29, N 3.59, S
7.35. HRMS: calcd. for C27H19NO2S [M]+ 421.1136; found
421.1139.
16f: The domino reaction of 15 (0.3 g, 0.625 mmol) with benzo[b]-
furan (0.08 g, 0.687 mmol) in dry 1,2-DCE (5 mL) in the presence
of ZnBr2 (0.03 g, 0.125 mmol) following the above general pro-
(s, 3 H, C6H13-H), 1.08 (s, 10 H, C6H13-H), 0.75 (t, J = 6.6 Hz, 9
H, C6H13-H) ppm. 13C NMR (125 MHz, CDCl3): δ = 151.8 (2 C),
145.1, 145.0, 141.1, 139.9, 139.4, 139.0, 137.8, 137.6, 136.4, 133.8,
133.6, 132.9, 129.0, 128.0, 127.6, 126.6, 126.5, 125.5, 125.4, 125.0,
cedure for heteroarenes afforded 16f (0.19 g, 76%) as a colourless
1
solid; m.p. 208–210 °C. H NMR (300 MHz, CDCl3): δ = 8.89 (s, 124.6, 124.1, 123.0, 120.6, 120.3, 120.2, 120.0, 118.5, 115.4, 113.8,
1 H, ArH), 8.34 (d, J = 8.1 Hz, 1 H, ArH), 8.12 (d, J = 7.5 Hz, 1
H, ArH), 7.93 (t, J = 7.5 Hz, 2 H, ArH), 7.79 (d, J = 8.1 Hz, 2 H,
ArH), 7.59–7.50 (m, 3 H, ArH), 7.40 (t, J = 7.35 Hz, 3 H, ArH),
108.4, 55.3, 40.4, 31.4, 29.6, 23.7, 22.5, 13.9 ppm. 13C NMR
(DEPT 135, 125 MHz, CDCl3): δ = 133.8, 129.0, 128.1, 127.6,
126.5, 125.5, 125.0, 124.6, 124.2, 123.0, 120.6, 120.3, 120.2, 120.0,
7.29–7.24 (m, 2 H, ArH) ppm. 13C NMR (125 MHz, CDCl3): δ = 118.5, 115.4, 113.8, 108.4, 40.4, 31.4, 29.6, 23.7, 22.7, 14.0 ppm.
157.2, 153.5, 139.3, 137.5, 134.8, 133.8, 129.0, 127.7, 127.6, 126.7
(2 C), 126.4, 124.5, 124.4, 124.1, 122.8, 120.9, 120.1, 115.5, 111.7,
107.0, 102.1 ppm. 13C NMR (DEPT 90, 125 MHz, CDCl3): δ =
MS (EI): m/z (%) = 778 (23) [M]+. C49H47NO2S3 (777.27): calcd.
C 75.64, H 6.09, N 1.80, S 12.36; found C 75.94, H 5.84, N 2.08,
S 12.05.
932
www.eurjoc.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 922–935

Synthesis of Aryl/Heteroaryl-Fused Carbazoles
18: The reaction of 17 (1.0 g, 8.333 mmol) with acetic anhydride
(15 mL) in the presence of InBr3 (0.03 g, 0.083 mmol) following the
same procedure as that used for 5a afforded 2-methyl-1-(diacetoxy-
methyl)benzene (1.61 g, 87%) as a colourless solid. The reaction of
2-methyl-1-(diacetoxymethyl)benzene (1.0 g, 4.504 mmol) with fi-
nely powdered NBS (0.88 g, 4.954 mmol) and AIBN (0.05 g) in dry
CCl4 (50 mL) following the same procedure as that used for 5a
afforded compound 18 (1.23 g, 91%) as a colourless liquid. 1H
NMR (300 MHz, CDCl3): δ = 7.85 (s, 1 H, benzylic CH), 7.54 (d,
J = 2.1 Hz, 1 H, ArH), 7.42–7.36 (m, 3 H, ArH), 4.73 (s, 2 H,
benzylic CH2), 2.14 (s, 6 H, 2-CH3) ppm. 13C NMR (CDCl3,
75 MHz): δ = 168.6, 136.2, 133.6, 131.4, 130.3, 128.9, 128.4, 88.6,
29.9, 20.9 ppm. MS (EI): m/z (%) = 301 (17) [M]2+, 299 (17) [M]+.
C12H13BrO4 (299.99): calcd. C 47.86, H 4.35; found C 47.59, H
4.61.
with ethyl acetate (3ϫ10 mL) and dried (Na2SO4). Removal of the
solvent followed by silica gel column chromatographic purification
(n-hexane) led to the isolation of annulated naphthalene 20a as a
colourless solid; yield 0.12 g (63%); m.p. 176–178 °C. 1H NMR
(300 MHz, CDCl3): δ = 8.21 (s, 1 H, ArH), 8.10 (s, 1 H, ArH),
7.92–7.84 (m, 2 H, ArH), 7.44–7.40 (m, 2 H, ArH), 7.03 (s, 1 H,
ArH), 2.60 (s, 3 H, CH3) ppm. 13C NMR (75.4 MHz, CDCl3): δ =
142.7, 139.9, 138.8, 131.0, 130.5, 128.0, 127.2, 124.8, 124.7, 120.9,
120.3, 120.0, 16.6 ppm. 13C NMR (DEPT 90, 75.4 MHz, CDCl3):
δ = 128.0, 127.2, 124.8, 124.7, 120.9, 120.3, 120.0 ppm. MS (EI):
m/z (%) = 198 (57) [M]+. C13H10S (198.05): calcd. C 78.75, H 5.08,
S 16.17; found C 78.47, H 5.31, S 15.92.
20d: The domino reaction of 18 (0.3 g, 0.996 mmol) with 1-methyl-
naphthalene (0.28 g, 1.993 mmol) in dry 1,2-DCE (5 mL) in the
presence of ZnBr2 (0.04 g, 0.199 mmol) following the same pro-
cedure as that used for 20a afforded 20d (0.15 g, 61%) as a colour-
less solid; m.p. 182–184 °C. 1H NMR (300 MHz, CDCl3): δ = 8.03
(d, J = 8.1 Hz, 2 H, ArH), 7.50 (t, J = 3.75 Hz, 2 H, ArH), 7.39
(dd, J = 1.2, J = 1.2 Hz, 1 H, ArH), 7.26–7.19 (m, 2 H, ArH), 7.08
(td, J = 1.2, J = 1.5, J = 1.5 Hz, 2 H, ArH), 6.77–6.70 (m, 2 H,
ArH), 2.66 (s, 3 H, CH3) ppm. 13C NMR (75.4 MHz, CDCl3): δ =
143.6, 137.5, 135.5, 133.6, 133.2, 132.0, 131.2, 130.5, 129.0, 127.4,
19a: ZnBr2 (0.04 g, 0.199 mmol) was added to a solution of bromo
compound 18 (0.3 g, 0.996 mmol) and 2-methylthiophene (0.12 g,
1.196 mmol) in dry 1,2-DCE (5 mL). It was then stirred at room
temperature for 16 h under N2. The reaction mixture was quenched
with ice/water (5 mL), extracted with ethyl acetate (3ϫ10 mL) and
dried (Na2SO4). Removal of the solvent followed by silica gel col-
umn chromatographic purification (hexane/ethyl acetate, 98:2) fur-
nished diarylated bromo compound 19a (0.16 g, 42%) as a colour-
127.2, 126.1, 125.9, 125.5, 125.3, 124.8, 124.7, 124.5, 19.5 ppm. 13
C
1
less solid; m.p. Ͼ320 °C. H NMR (300 MHz, CDCl3): δ = 7.29–
NMR (DEPT 135, 75.4 MHz, CDCl3): δ = 131.2, 130.5, 129.0,
127.4, 127.2, 126.1, 125.9, 125.6, 125.3, 124.9, 124.7, 19.6 ppm. MS
(EI): m/z (%) = 242 (38) [M]+. C19H14 (242.10): calcd. C 94.18, H
5.82; found C 94.49, H 5.56.
7.24 (m, 4 H, ArH), 6.57 (s, 4 H, ArH), 6.16 (s, 1 H, benzylic CH),
4.49 (s, 2 H, benzylic CH2), 2.41 (s, 6 H, 2-CH3) ppm. 13C NMR
(75.4 MHz, CDCl3): δ = 144.2, 143.0, 139.3, 135.1, 130.5, 129.3,
129.2, 127.5, 126.1, 124.6, 42.8, 31.5, 15.3 ppm. MS (EI): m/z (%)
= 377 (32) [M]2+, 375 (32) [M]+. C18H17BrS2 (375.99): calcd. C
57.29, H 4.54, S 16.99; found C 57.57, H 4.28, S 17.25.
21: Potassium acetate (0.19 g, 1.993 mmol) was added to a solution
of bromo compound 18 (0.3 g, 0.996 mmol) in dry THF. The mix-
ture was then stirred at room temperature under nitrogen for 4 h.
The solvent was removed and the residue was extracted with ethyl
acetate (2ϫ10 mL) and dried (Na2SO4). Removal of the solvent
followed by silica gel column chromatographic purification (n-hex-
ane) led to the isolation of triacetate 21 (0.21 g, 75%) as a colour-
less liquid. 1H NMR (300 MHz, CDCl3): δ = 7.85 (s, 1 H, benzylic
CH), 7.57–7.54 (m, 1 H, ArH), 7.42–7.35 (m, 3 H, ArH), 4.72 (s, 2
H, benzylic CH2), 2.13 (s, 9 H, 3-CH3) ppm. 13C NMR (75.4 MHz,
CDCl3): δ = 168.6, 136.2, 133.6, 131.4, 130.3, 128.9, 128.4, 88.5,
29.9, 25.1, 20.9. 20.7 ppm. MS (EI): m/z (%) = 280 (45) [M]+.
C14H16O6 (280.09): calcd. C 59.99, H 5.75; found C 59.71, H 5.98.
19b: The reaction of 18 (0.3 g, 0.996 mmol) with benzo[b]thiophene
(0.16 g, 1.196 mmol) in dry 1,2-DCE (5 mL) in the presence of
ZnBr2 (0.04 g, 0.199 mmol) following the same procedure as that
used for 19a afforded 19b (0.21 g, 46%) as a colourless solid; m.p.
1
162–164 °C. H NMR (300 MHz, CDCl3): δ = 7.88–7.74 (m, 4 H,
ArH), 7.42–7.17 (m, 8 H, ArH), 6.95 (s, 1 H, ArH), 6.69 (s, 1 H,
ArH), 6.51 (s, 1 H, benzylic CH), 4.40 (s, 2 H, benzylic CH2) ppm.
13C NMR (75.4 MHz, CDCl3): δ = 140.9, 140.7, 138.3, 137.1,
135.6, 131.1, 129.3, 129.1, 127.7, 125.3, 124.6, 124.4, 122.8, 122.6,
40.9, 31.9 ppm. 13C NMR (DEPT 135, 75.4 MHz, CDCl3): δ =
131.1, 129.3, 129.1, 127.7, 125.3, 124.6, 124.4, 122.8, 122.6, 40.9,
31.9 ppm. MS (EI): m/z (%) = 449 (41) [M]2+, 447 (41) [M]+.
C24H17BrS2 (447.99): calcd. C 64.14, H 3.81, S 14.27; found C
63.89, H 4.02, S 14.01.
22: Benzo[b]furan (0.14 g, 1.178 mmol) and ZnBr2 (0.05 g,
0.214 mmol) were added to a solution of triacetate 21 (0.30 g,
1.071 mmol) in dry 1,2-DCE (10 mL). The mixture was then stirred
at room temperature under nitrogen for 1 h and then heated at
reflux for 1 h. The solvent was removed and the residue was ex-
tracted with ethyl acetate (2ϫ10 mL) and dried (Na2SO4). Re-
moval of the solvent followed by silica gel column chromatographic
purification (n-hexane) afforded benzonaphtho[b]furan 22 as pale-
yellow solid; yield 0.13 g (58%); m.p. 284–286 °C. 1H NMR
(300 MHz, CDCl3): δ = 8.41 (s, 1 H, ArH), 8.05 (t, J = 9.3 Hz, 2
H, ArH), 7.96 (d, J = 8.1 Hz, 1 H, ArH), 7.92 (s, 1 H, ArH), 7.59–
7.47 (m, 4 H, ArH), 7.37 (t, J = 7.35 Hz, 1 H, ArH) ppm. 13C
NMR (75.4 MHz, CDCl3): δ = 157.6, 154.8, 133.0, 130.1, 128.3,
127.7, 125.8, 125.4, 124.3, 123.9, 122.7, 121.2, 119.1, 111.5,
106.9 ppm. MS (EI): m/z (%) = 218 (55) [M]+. C16H10O (218.07):
calcd. C 88.05, H 4.62; found C 88.33, H 4.37.
Single-crystal X-ray analysis of 19b, all calculations were per-
formed with the SHELXL-97 program.[21] Crystal data for 19b:
C24H17BrS2, MW = 449.42 gmol–1, monoclinic crystal system,
space group P21/c, Z = 4, a = 10.4881(6), b = 9.2373(5), c =
20.9512(11) Å, α = γ = 90°, β = 91.547(4)°, V = 2029.05(19) Å3 and
Dcalcd. = 1.471 Mgm–3. In total, 19828 independent reflections were
collected of which 9445 were considered as observed [IϾ2σ(I)]. The
structure was solved by direct methods and refined by full-matrix
least-squares procedures to give a final R value of 4.84%.
CCDC-793488 contains the supplementary crystallographic data
for 19b. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
23: The domino reaction of 21 (0.30 g, 1.071 mmol) with N-pent-
ylindole (0.22 g, 1.178 mmol) in dry 1,2-DCE (5 mL) in the pres-
ence of ZnBr2 (0.05 g, 0.214 mmol) following a procedure similar
to that used for 22 afforded 23 (0.18 g, 58%) as a brown solid; m.p.
20a: ZnBr2 (0.04 g, 0.199 mmol) was added to a solution of bromo
compound 18 (0.3 g, 0.996 mmol) and 2-methylthiophene (0.19 g,
1.993 mmol) in dry 1,2-DCE (5 mL). It was then stirred at room
temperature for 1 h under N2 and then heated at reflux for 4 h. The
reaction mixture was quenched with ice/water (5 mL), extracted
1
260–262 °C. H NMR (300 MHz, CDCl3): δ = 8.79 (s, 1 H, ArH),
8.65 (d, J = 2.4 Hz, 2 H, ArH), 8.50 (s, 1 H, ArH), 8.05 (d, J =
Eur. J. Org. Chem. 2011, 922–935
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
933

A. K. Mohanakrishnan et al.
268–270 °C. H NMR (300 MHz, CDCl3): δ = 8.43 (s, 1 H, ArH),
FULL PAPER
1
7.8 Hz, 2 H, ArH), 7.63 (s, 1 H, ArH), 7.50–7.43 (m, 3 H, ArH),
4.32 (t, J = 7.2 Hz, 2 H, C5H11-H), 2.00 (q, J = 7.2 Hz, 2 H, C5H11- 8.13 (s, 1 H, ArH), 7.10 (s, 1 H, ArH), 2.63 (s, 3 H, CH3) ppm. 13
C
H), 1.49–1.42 (m, 4 H, C5H11-H), 0.92 (t, J = 7.05 Hz, 3 H, C5H11-
NMR (75.4 MHz, CDCl3): δ = 142.4, 139.2, 138.1, 135.4, 124.8,
H) ppm. 13C NMR (75.4 MHz, CDCl3): δ = 134.0, 131.8, 129.7, 124.4, 122.8, 121.3, 19.2 ppm. MS (EI): m/z (%) = 324 (18) [M]+.
128.6, 128.2, 127.5, 127.0, 126.8, 126.0, 125.3, 123.9, 122.8, 120.1,
C18H12S3 (324.01): calcd. C 66.63, H 3.73, S 29.65; found C 66.42,
119.8, 102.1, 100.4, 43.3, 29.6, 27.5, 22.6, 14.0 ppm. 13C NMR H 3.98, S 29.34.
(DEPT 135, 75.4 MHz, CDCl3): δ = 127.5, 127.0, 126.8, 123.9 (2
Supporting Information (see footnote on the first page of this arti-
C), 122.7, 120.1, 119.8, 102.1, 100.4, 43.3, 29.5, 27.5, 22.6,
14.0 ppm. MS (EI): m/z (%) = 287 (46) [M]+. C21H21N (287.16):
calcd. C 87.76, H 7.36, N 4.87; found C 87.53, H 7.56, N 4.58.
cle): Experimental procedures and characterization data for the
known annulated carbazoles 7a–f, 7h–p, 9b, 16a–c, 16e and annu-
lated thiophenes 20b, 20c.
24: The domino reaction of 21 (0.30 g, 1.071 mmol) with 9-(2-eth-
ylhexyl)-9H-carbazole (0.33 g, 1.178 mmol) in dry 1,2-DCE (5 mL)
in the presence of ZnBr2 (0.05 g, 0.214 mmol) following a pro-
cedure similar to that used for 22 afforded 24 (0.26 g, 64%) as a
yellow solid; m.p. 264–266 °C. 1H NMR (300 MHz, CDCl3): δ =
9.24 (s, 1 H, ArH), 8.76 (d, J = 6.6 Hz, 1 H, ArH), 8.55 (s, 1 H,
ArH), 8.17 (d, J = 8.4 Hz, 1 H, ArH), 8.06–7.99 (m, 2 H, ArH),
7.66 (d, J = 9.3 Hz, 1 H, ArH), 7.59–7.47 (m, 5 H, ArH), 4.33 (dd,
J = 1.8, J = 2.1 Hz, 2 H, C8H17-H), 2.10 (m, 1 H, C8H17-H), 1.42–
1.25 (m, 7 H, C8H17-H), 0.94–0.83 (m, 7 H, C8H17-H) ppm. 13C
NMR (75.4 MHz, CDCl3): δ = 139.2, 137.7, 132.5, 129.5, 128.7,
128.2, 127.9, 127.8, 125.6, 124.2, 123.8, 123.4, 121.7, 120.6, 120.0,
113.1, 112.6, 109.8, 47.4, 40.0, 31.0, 28.8, 24.4, 23.0, 14.0,
10.9 ppm. 13C NMR (DEPT 135, 75.4 MHz, CDCl3): δ = 128.2,
127.9, 127.8, 125.6, 124.2, 123.4, 121.7, 120.6, 120.0, 112.6, 109.8,
47.4, 40.0, 31.0, 28.8, 24.4, 23.0, 14.0, 10.9 ppm. MS (EI): m/z (%)
= 379 (29) [M]+. C28H29N (379.23): calcd. C 88.61, H 7.70, N 3.69;
found C 88.89, H 7.44, N 3.88.
Acknowledgments
We thank the Department of Science and Technology (DST), New
Delhi for financial support. R. S. thanks the University Grants
Commission (UGC), New Delhi for an SRF fellowship. V. D.
thanks the Council of Scientific and Industrial Research (CSIR)
for an SRF fellowship. The authors thank the Department of Sci-
ence and Technology Funds for the Improvement of Science and
Technology (DST-FIST) for a 300 MHz NMR facility. The authors
also thank the University of Madras for a Department of Science
and Technology Promotion of University Research and Scientific
Excellence (DST-PURSE) grant.
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26: The reaction of 25 (1.0 g, 5.95 mmol) with acetic anhydride
(15 mL) in the presence of InBr3 (0.02 g, 0.06 mmol) following the
same procedure as that used for 5a afforded 3,4-bis(diacetoxy-
methyl)-2,5-dimethylthiophene (1.98 g, 90%) as a brown solid. A
solution of 3,4-bis(diacetoxymethyl)-2,5-dimethylthiophene (1.0 g,
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2.13 (s, 12 H, 4-CH3) ppm. 13C NMR (75.4 MHz, CDCl3): δ =
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0.226 mmol) were added to a solution of dibromo compound 26
(0.30 g, 0.566 mmol) in dry 1,2-DCE (10 mL). The mixture was
then stirred at room temperature under nitrogen for 1 h. The sol-
vent was removed and the residue was extracted with ethyl acetate
(2ϫ10 mL) and dried (Na2SO4). Removal of the solvent followed
by silica gel column chromatographic purification (n-hexane) af-
forded annulated compound 27 (0.11 g, 54%) as a colourless solid;
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ArH), 8.11 (d, J = 7.2 Hz, 2 H, ArH), 7.99 (s, 2 H, ArH), 7.61 (d,
J = 7.5 Hz, 2 H, ArH), 7.51 (t, J = 7.35 Hz, 2 H, ArH), 7.42 (t, J
= 7.2 Hz, 2 H, ArH) ppm. 13C NMR (75.4 MHz, CDCl3): δ =
156.1, 154.8, 138.1, 130.9, 127.5, 123.5, 123.1, 122.2, 120.8, 113.4,
111.5, 105.4 ppm. MS (EI): m/z (%) = 364 (28) [M]+. C24H12O2S
(364.05): calcd. C 79.10, H 3.32, S 8.80; found C 79.35, H 3.10, S
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934
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Published Online: December 22, 2010
Eur. J. Org. Chem. 2011, 922–935
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
935