An improved synthesis of carbazoles via domino reaction of N-protected-2-methylindoles with DMF-DMA/DMA-DMA

Article abstract of DOI:10.1002/jhet.899

An efficient synthesis of carbazole analogs has been achieved via interaction of N-protected-2-methylindoles with N,N-dimethylformamide dimethylacetal as well as N,N-dimethylacetamide dimethylacetal in the presence of pyrrolidine or 1,4-diazabicyclo(2.2.2

Full text of DOI:10.1002/jhet.899

July 2012
An Improved Synthesis of Carbazoles via Domino Reaction of
N-Protected-2-methylindoles with DMF-DMA/DMA-DMA
913
*
Radhakrishnan Sureshbabu and Arasambattu K. Mohanakrishnan
Department of Organic Chemistry, University of Madras, Guindy Campus,
Chennai 600 025, Tamil Nadu, India
*
E-mail: mohanakrishnan@unom.ac.in
Received December 24, 2010
DOI 10.1002/jhet.899
View this article online at wileyonlinelibrary.com.
An efficient synthesis of carbazole analogs has been achieved via interaction of N-protected-2-methyl-
indoles with N,N-dimethylformamide dimethylacetal as well as N,N-dimethylacetamide dimethylacetal
in the presence of pyrrolidine or 1,4-diazabicyclo(2.2.2)octane (DABCO).
J. Heterocyclic Chem., 49, 913 (2012).
INTRODUCTION
substituted carbazoles 2 in moderate yields via interaction
of 1-phenylsulfonyl-2/(3)-methyl-3/(2)-vinylindoles 1 with
DMF-DMA/N,N-dimethylacetamide dimethylacetal (DMA-
DMA) (Scheme 1).
Development of new methods for the synthesis of car-
bazole and its derivatives is of current interest because
increasing number of carbazole alkaloids have displayed
varied biological activities [1–3]. Recently, the synthesis
of benz-annulated carbazoles received considerable atten-
tion due to their antitumor [4] and anti-inflammatory
activities [5]. The carbazole derivatives are also widely
useful owing to their photorefractive, photoconductive,
hole-transporting, and light-emitting properties [6]. The
dihydroindolo carbazole derivatives could be used as
active materials for organic light-emitting diodes [7], or-
ganic field-effect transistors [8], organic thin-film transis-
tors [9], and photovoltaic cells [10]. Over the years, the
thermal electrocyclization methodology has been widely
used for the synthesis of carbazole-based natural products
[11]. Recently, Konakahara and coworkers [12] described
a Me3SiCl-mediated three-component coupling reaction
of a functionalized enamine, N,N-dimethylformamide
diethylacetal, and an internal alkyne having an electron
withdrawing group to afford pyridine derivatives. Tois
et al. [13] reported a rapid two-step synthesis of 4(1H)quin-
olones via interaction of o-nitroacetophenone with N,N-
dimethylformamide·dimethylacetal (DMF-DMA) followed
by reductive cyclization. Hua et al. [14] synthesized dis-
ubstituted dihydronaphthalenes with high yields by the
cycloaddition of vinylarenes with electron-deficient
alkynes in the presence of DMF-DMA.
Even though this methodology was found to be facile
with a variety of 2-methyl-3-vinylindoles 1, carbazoles
2 could be obtained only in moderate yields. Hence, to
increase the yields of the substituted carbazoles, differ-
ent reaction parameters including solvent and reaction
temperature were varied. But these variations were
found to be of no use. Finally, the use of pyrrolidine
was proved pivotal for the formation of desired products
in good yields. Thus, the reaction of 2-methylindoles
1a–d with 2 equiv of DMF-DMA or DMA-DMA in the
presence of pyrrolidine afforded substituted carbazoles
in 67–80% yields (Scheme 2).
It has been proved that the use of highly reactive pyr-
rolidine acetal or in situ generation of the same via
addition of pyrrolidine with DMF-DMA has signifi-
cantly enhanced the rate of enamine formation [17].
Hence, we reasoned that the better yield of 2a–d/3a–c
obtained in the presence of pyrrolidine might be due to
the enhanced rate of formation of the required enamine
(Scheme 3).
A list of various types of 2-methylindoles 1a–d used,
reaction conditions, the respective carbazoles 2a–d/3a–c,
and the yields obtained are summarized in Table 1.
Always enhanced yields of carbazoles were obtained
when the domino reaction of 2-methylindole was per-
formed in the presence of pyrrolidine. The reaction of
2-methyl-3-vinylester indoles 1a–b with DMF-DMA/
DMA-DMA afforded the corresponding carbazoles 2a
and 2b/3a and 3b in better yields (entry 1 and 2), and
RESULTS AND DISCUSSION
In continuation of our interest on annulated carbazole
analogs [15], we have reported [16] the synthesis of
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R. Sureshbabu and A. K. Mohanakrishnan
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Scheme 1. Annulation of 2-methylindole 1 with DMF-DMA/DMA-DMA.
Scheme 3. Mechanistic rationale for the formation of 2a.
also enhanced yield of the carbazole 2c/3c was obtained
with the 5-methoxyindole 1c (entry 3). Always, the
interaction of 2-methyl-3-vinylindoles 1a–c with DMF-
DMA gave carbazoles 2a–c in better yields than the cor-
responding carbazoles 3a–c obtained using DMA-DMA.
Similarly, the reaction of 2-methylindole having vinyl
ketone functionality at the indol 3-position 1d with
DMF-DMA furnished the respective carbazole 2d in
67% yield (entry 4).
As a representative case, the domino reaction of 2-
methyl-3-vinylindole 1b with DMF-DMA in the pres-
ence of 0.2 equiv of DABCO afforded N-phenylsulfonyl
cleaved carbazole 9a in 62% yield. Gratifyingly, when
the interaction of 1b was performed with DMF-DMA in
the presence of 1 equiv of DABCO gave N-methylated
carbazole 9b in 63% yield. However, the interaction of
1b with DMA-DMA in the presence of 1 equiv of
DABCO led to the isolation of N-methylated-2-methyl-
3-vinyl indole 10 (Scheme 4).
The annulation of 1-phenylsulfonyl-2-methyl-3-acetyl
indole 1e with DMF-DMA at 110ꢀC for 4 h led to the
isolation of N-phenylsulfonyl-4-hydroxycarbazole-3-car-
boxaldehyde 11 in 65% yield. In our earlier report
[16b], we wrongly assigned the structure as N-phenyl-
sulfonyl-4-hydroxycarbazole-1-carboxaldehyde 12. The
structure of N-phenylsulfonyl-4-hydroxycarbazole-3-car-
boxaldehyde 11 was confirmed by matching its melting
point and spectral data with an authentic sample pre-
pared using Michael addition methodology [18]. The
annulation of 1e with DMF-DMA in the presence of
pyrrolidine has slightly increased the yield of the
carbazole 11. The interaction of 1e with DMF-DMA in
presence of DABCO led to the isolation of 4-hydroxycar-
bazole-3-carboxaldehyde 13 in 68% yield. The initial reac-
tion of 1e with DMF-DMA may lead to the formation of
bis-enamine 14. Electrocyclization of enamine 14 followed
by the elimination of dimethyl amine and subsequent work
up led to the formation of compound 11 (Scheme 5).
Surprisingly, the reaction of 1e with DMA-DMA at
110ꢀC gave 4-amino carbazole 16 in 52% yield. The
mechanism of formation of amino carbazole 16 can be
visualized through intramolecular Michael addition of
carbanion 17 followed by the addition of dimethyla-
mide and subsequent elimination of water molecule
(Scheme 6).
The domino reaction of 2-methyl-3-vinylnitro indole
1f [19] with DMF-DMA at 110ꢀC for 4 h yielded 3-
nitro-2-indolylcarbazole 19 in 48% yield. The formation
of 19 can be realized through the Diels–Alder reaction
of quino-dimethane intermediate 20 with 1f to afford in-
termediate 21. The latter on elimination of nitromethane
may lead to carbazole 19 (Scheme 7).
The annulation of malonylidene tethered 2-methylindole 1g
[11c] with DMF-DMA led to the isolation of carbazole 2a in
70% yield. The initial reaction of 1g with DMF-DMA led to
the formation of enamine 22, which on electrocyclization fol-
lowed by elimination of ethyl dimethylcarbamate gave the
carbazole 2a (Scheme 8).
Finally, the reaction of 3-carbethoxy 2-methylindole
1h with DMF-DMA/DMA-DMA afforded indolylmethyl
aldehyde 24/N-methylated indole 25 in 75 and 59%
yields, respectively, whereas 2-methyl-3-benzoylindole
1i on reaction with DMF-DMA gave an inseparable
mixture of indolylmethyl aldehyde 26 and enamino in-
dole 27 (Scheme 9).
Scheme 2. Tandem reaction of 2-methylindoles 1a–d with DMF-DMA/
DMA-DMA in the presence of pyrrolidine.
CONCLUSIONS
In conclusion, we have achieved an improved synthe-
sis of substituted carbazoles via interaction of 2-methyl-
indoles 1a–e with DMF-DMA/DMA-DMA in the
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An Improved Synthesis of Carbazoles via Domino Reaction of
N-Protected-2-methylindoles with DMF-DMA/DMA-DMA
915
Table 1
Synthesis of substituted carbazoles 2a–d/3a–c.
Entry
1
Vinylindoles
Condition
Carbazole
Yield (%)a
Pyrrolidine, DMF-DMA
Pyrrolidine, DMA-DMA
80
75
2
3
4
Pyrrolidine, DMF-DMA
Pyrrolidine, DMA-DMA
78
77
Pyrrolidine, DMF-DMA
Pyrrolidine, DMA-DMA
74
69
Pyrrolidine, DMF-DMA
67
aIsolated yield after column chromatography.
Scheme 5. Tandem reaction of 2-methyl-3-acetylindole 1e with
DMF-DMA.
Scheme 4. Tandem reaction of 2-methylindole 1b with DMF-DMA/
DMA-DMA in the presence of DABCO.
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R. Sureshbabu and A. K. Mohanakrishnan
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Scheme 6. Tandem reaction of 2-methyl-3-acetylindole 1e with DMA-DMA.
Scheme 8. Tandem reaction of 2-methylindole 1g with DMF-DMA.
added. The reaction mixture was heated at 110ꢀC for 4 h under
nitrogen atmosphere. It was poured in to crushed ice (50 g)
containing few drops of concentrated HCl and extracted with
CHCl3 (2 Â 20 mL). The combined extracts were washed with
water (10 mL), brine (10 mL) and dried (Na2SO4). Removal
of solvent followed by column chromatographic purification
(20% EA/hexane) afforded carbazoles 2a–d.
presence of pyrrolidine. As a representative case, the
tandem reaction of 2-methylindole 1b with varying
amount of DABCO led to the isolation of N-free as well
as N-methyl carbazoles. Further, the tandem reaction of
2-methylindoles 1e–i with DMF-DMA/DMA-DMA was
also performed. The mechanistic pathways for the for-
mation of carbazole derivatives are also proposed.
Ethyl 9-(phenylsulfonyl)-9H-carbazole-3-carboxylate (2a).
This compound was obtained as colorless solid (0.41 g, 80%),
mp: 178–180ꢀC (Lit. [16] 180ꢀC); IR (KBr): 1709 (—CO2Et),
1
1369 and 1176 (—SO2Ph) cmÀ1. H-NMR (CDCl3, 300 MHz):
d 8.53 (s, 1 H), 8.31–8.25 (m, 2 H), 8.11 (dd, J = 1.5 Hz,
J = 1.5 Hz, 1 H), 7.90 (d, J = 7.5 Hz, 1 H), 7.75 (d, J = 8.1 Hz,
2 H), 7.49–7.24 (m, 5 H), 4.35 (q, J = 7.1 Hz, 2 H), 1.36
(t, J = 7.2 Hz, 3 H).
EXPERIMENTAL
All melting points were uncorrected. Reagents were pur-
chased from commercial sources and used as received without
purification. Solvents were dried by standard procedures. Col-
umn chromatography was carried on silica gel (grade 60, mesh
size 230–400, Merck). IR spectra were recorded on a SHI-
MADZU FT-IR 8300 instrument. 1H- and 13C-NMR spectra
were recorded in CDCl3 using tetramethylsilane (TMS) as an
internal standard on a Bruker-300 spectrometer. Chemical shift
values were quoted in ppm, and coupling constants were quoted
in Hz. Chemical shift multiplicities were reported as s = singlet,
d = doublet, t = triplet, q = quartet, and m = multiplet. Mass
spectra were recorded on a JEOL DX 303 HF spectrometer. Ele-
mental analyses were carried out on Perkin-Elmer series II 2400
(IIT Madras) equipment. The required 2-methyl-3-vinylester
indoles 1a–d are prepared from the corresponding 2-methylindole-
3-carboxaldehyde following the published procedure [20].
Ethyl 2-methyl-9-(phenylsulfonyl)-9H-carbazole-3-carboxylate
(3a). This compound was obtained as colorless solid (0.40 g,
75%), mp: 174–176ꢀC (Lit. [16] 174ꢀC); IR (KBr): 1712
1
(—CO2Et), 1360 and 1174 (—SO2Ph) cmÀ1. H-NMR (CDCl3,
300 MHz): d 8.47 (s, 1 H), 8.29 (d, J = 8.1 Hz, 1 H), 8.20 (s,
1 H), 7.91 (d, J = 7.5 Hz, 1 H), 7.82 (d, J = 7.5 Hz, 2 H),
7.51–7.44 (m, 2 H), 7.39–7.31 (m, 3 H), 4.40 (q, J = 7.1 Hz,
2 H), 2.80 (s, 3 H), 1.43 (t, J = 7.05 Hz, 3 H).
Methyl 9-(phenylsulfonyl)-9H-carbazole-3-carboxylate (2b).
This compound was obtained as colorless solid (0.40 g, 78%), mp:
188–190ꢀC (Lit. [16] 188ꢀC); IR (KBr): 1710 (—CO2Me), 1354
1
and 1170 (—SO2Ph) cmÀ1. H-NMR (CDCl3, 300 MHz): d 8.61
(d, J = 1.5 Hz, 1 H), 8.39–8.32 (m, 2 H), 8.18 (dd, J = 1.5 Hz,
J = 1.5 Hz, 1 H), 7.97 (d, J = 7.5 Hz, 1 H), 7.84 (d, J = 7.8 Hz,
2 H), 7.54–7.32 (m, 5 H), 3.97 (s, 3 H).
A representative procedure for the domino reaction of
2-methylindoles 1a–d with DMF-DMA/DMA-DMA in the
presence of pyrrolidine. To a stirred solution of 2-methyl-3-
vinylindoles 1a–d (1.35 mmol) in dry DMF (1.5 mL), DMF-
DMA/DMA-DMA (2.71 mmol) and pyrrolidine (0.5 mL) were
Methyl 2-methyl-9-(phenylsulfonyl)-9H-carbazole-3-carboxylate
(3b). This compound was obtained as colorless solid (0.41 g,
77%), mp: 170–172ꢀC (Lit. [16] 171ꢀC); IR (KBr): 1720
(—CO2Me), 1369 and 1172 (—SO2Ph) cmÀ1
.
1H-NMR
(CDCl3, 300 MHz): d 8.51 (s, 1 H), 8.31 (d, J = 8.1 Hz, 1 H),
Scheme 7. Tandem reaction of 2-methyl-3-vinylnitro indole 1f with
DMF-DMA.
Scheme 9. Tandem reaction of 2-methylindole 1h and 1i with DMF-DMA/
DMA-DMA.
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An Improved Synthesis of Carbazoles via Domino Reaction of
N-Protected-2-methylindoles with DMF-DMA/DMA-DMA
917
8.23 (s, 1 H), 7.94–7.84 (m, 3 H), 7.50–7.28 (m, 5 H), 3.96 (s,
3 H), 2.83 (s, 3 H).
3.73 (s, 3 H), 3.57 (s, 3 H), 2.42 (s, 3 H). 13C-NMR (CDCl3,
75 MHz): d 169.1, 141.8, 137.9, 137.5, 125.6, 122.1, 121.3,
120.0, 111.0, 109.3, 109.0, 51.2, 29.8, 10.6. MS (EI) m/z: 229
[M+]. Anal. calcd. for C14H15NO2: C, 73.34; H, 6.59; N, 6.11.
Found: C, 73.09; H, 6.81; N, 5.88.
Methyl 6-methoxy-9-(phenylsulfonyl)-9H-carbazole-3-
carboxylate (2c). This compound was obtained as colorless
solid (0.38 g, 74%), mp: 182–184ꢀC (Lit. [16] 183ꢀC);
IR (KBr): 1698 (—CO2Me), 1354 and 1168 (—SO2Ph) cmÀ1
.
9-Phenylsulfonyl-4-hydroxycarbazole-3-carbaldehyde (11).
This compound was obtained as pale brown solid (0.36 g, 65%),
mp: 190–192ꢀC; IR (KBr): 3340 (—OH), 1648 (—CHO), 1366
1H-NMR (CDCl3, 300 MHz): d 8.52 (s, 1 H), 8.32 (d, J = 7.5
Hz, 1 H), 8.19 (t, J = 8.2 Hz, 2 H), 7.76–7.72 (m, 2 H),
7.44–7.30 (m, 4 H), 7.10 (d, J = 6.6 Hz, 1 H), 3.95 (s, 3 H),
3.88 (s, 3 H).
and 1158 (—SO2Ph) cmÀ1 1H-NMR (CDCl3, 300 MHz):
.
d 12.01 (s, 1 H), 9.94 (s, 1 H), 8.30 (t, J = 7.3 Hz, 2 H),
7.99 (d, J = 8.7 Hz, 1 H), 7.86 (d, J = 7.8 Hz, 2 H), 7.62 (d,
J = 8.7 Hz, 1 H), 7.53–7.35 (m, 5 H). 13C-NMR (CDCl3, 75
MHz): d 195.8, 158.6, 143.9, 137.9, 137.8, 134.2, 132.3,
129.3, 127.2, 126.5, 124.8, 124.7, 123.4, 116.4, 114.6, 114.4,
106.9. MS (EI) m/z: 351 [M+]. Anal. calcd. for C19H13NO4S:
C, 64.95; H, 3.73; N, 3.99. Found: C, 65.25; H, 3.46; N,
4.30.
Methyl 6-methoxy-2-methyl-9-(phenylsulfonyl)-9H-carbazole-
3-carboxylate (3c). This compound was obtained as colorless
solid (0.37 g, 69%), mp: 174–176ꢀC (Lit. [16] 175ꢀC); IR (KBr):
1702 (—CO2Me), 1363 and 1166 (—SO2Ph) cmÀ1 1H-NMR
.
(CDCl3, 300 MHz): d 8.35 (s, 1 H), 8.11–8.09 (m, 2 H), 7.75–7.68
(m, 3 H), 7.40–7.22 (m, 3 H), 6.98 (d, J = 6.9 Hz, 1 H), 3.86 (s,
3 H), 3.80 (s, 3 H), 2.71 (s, 3 H).
4-Hydroxy-9H-carbazole-3-carbaldehyde (13). This
compound was obtained as dark brown solid (0.23 g, 68%),
mp: 114–116ꢀC; IR (KBr): 3352 (—OH), 3268 (—NH),
3-Acetyl 9-(phenylsulfonyl)-9H-carbazole (2d). This
compound was obtained as colorless solid (0.34 g, 67%), mp:
192–194ꢀC (Lit. [16] 192ꢀC); IR (KBr): 1670 (—COMe), 1382
1670 (—CHO) cmÀ1 1H-NMR (CDCl3, 300 MHz): d 12.34
.
and 1172 (—SO2Ph) cmÀ1 1H-NMR (CDCl3, 300 MHz):
.
(s, 1 H), 9.80 (s, 1 H), 8.29 (d, J = 7.8 Hz, 1 H), 7.42 (d,
J = 8.1 Hz, 1 H), 7.37 (d, J = 3.6 Hz, 2 H), 7.29–7.24 (m,
1 H), 7.18 (s, 1 H), 6.94 (d, J = 8.4 Hz, 1 H). 13C-NMR
(CDCl3, 75 MHz): d 195.1, 147.2, 131.3, 129.0, 127.9, 126.5,
125.8, 123.2, 121.3, 114.5, 113.5, 110.0, 103.5. MS (EI)
m/z: 211 [M+]. Anal. calcd. for C13H9NO2: C, 73.92; H,
4.29; N, 6.63. Found: C, 73.65; H, 4.51; N, 6.35.
d 8.59 (s, 1 H), 8.41–8.35 (m, 2 H), 8.11 (d, J = 8.7 Hz, 1 H),
7.99 (d, J = 8.1 Hz, 1 H), 7.84 (d, J = 7.2 Hz, 1 H), 7.55 (t,
J = 7.3 Hz, 2 H), 7.49–7.42 (m, 2 H), 7.30 (t, J = 7.6 Hz, 2 H),
2.70 (s, 3 H).
A representative procedure for the domino reaction of
2-methylindole 1b with DMF-DMA/DMA-DMA in the presence
of DABCO. To a stirred solution of 2-methyl-3-vinylindole 1b
(1.40 mmol) in dry DMF (1.5 mL), DMF-DMA/DMA-DMA
(2.81 mmol) and DABCO (0.28 mmol; 1.40 mmol of
DABCO was taken for 9b and 10) were added. The reaction
A representative procedure for the domino reaction of
2-methylindoles 1e–i with DMF-DMA/DMA-DMA. To a
stirred solution of 2-methylindoles 1e–i (1.40 mmol) in dry
DMF (1.5 mL), DMF-DMA/DMA-DMA (2.81 mmol) was
added. The reaction mixture was heated at 110ꢀC for 4 h under
nitrogen atmosphere. It was poured in to crushed ice (50 g)
containing few drops of concentrated HCl and extracted with
CHCl3 (2 Â 20 mL). The combined extracts were washed with
water (10 mL) and brine (10 mL) and dried (Na2SO4).
Removal of solvent followed by column chromatographic
purification (20% EA/hexane) afforded 16, 19, 2a, 24, 25, 26,
and 27.
mixture was heated at 110ꢀC for
4 h under nitrogen
atmosphere. It was poured in to crushed ice (50 g) containing
few drops of concentrated HCl and extracted with CHCl3
(2 Â 20 mL). The combined extracts were washed with water
(10 mL) and brine (10 mL) and dried (Na2SO4). Removal of
solvent followed by column chromatographic purification
(20% EA/hexane) afforded 9a, 9b, and 10.
Methyl 9H-carbazole-3-carboxylate (9a). This compound was
obtained as brown solid (0.20 g, 62%), mp: 170–172ꢀC; IR
(KBr): 3226 (—NH), 1706 (—CO2Me) cmÀ1
.
1H-NMR
9-Phenylsulfonyl-N,N,2-trimethylcarbazol-4-amine (16). This
compound was obtained as brown solid (0.30 g, 52%), mp:
(CDCl3, 300 MHz): d 8.74 (s, 1 H), 8.28 (s, 1 H), 8.08–8.04
(m, 2 H), 7.39–7.34 (m, 3 H), 7.26–7.21 (m, 1 H), 3.90 (s, 3
H). 13C-NMR (CDCl3, 75 MHz): d 167.8, 142.2, 139.9, 127.4,
126.5, 123.3, 123.1, 122.9, 121.4, 120.6, 120.3, 110.9, 110.1,
51.9. MS (EI) m/z: 225 [M+]. Anal. calcd. for C14H11NO2: C,
74.65; H, 4.92; N, 6.22. Found: C, 74.39; H, 5.11; N, 5.97.
Methyl 9-methyl-9H-carbazole-3-carboxylate (9b). This
compound was obtained as colorless solid (0.21 Àg1, 63%), mp:
192–194ꢀC; IR (KBr): 1354 and 1162 (—SO2Ph) cmÀ1
.
1H-NMR (CDCl3, 300 MHz): d 8.29 (d, J = 7.5 Hz, 1 H), 7.81
(t, J = 7.95 Hz, 3 H), 7.55 (s, 1 H), 7.42 (t, J = 7.2 Hz, 1 H),
7.30 (d, J = 6.9 Hz, 4 H), 6.55 (s, 1 H), 3.07 (s, 6 H), 2.67
(s, 3 H). 13C-NMR (CDCl3, 75 MHz): d 150.3, 140.6, 138.1,
138.0, 133.5, 133.4, 128.9, 127.9, 126.4, 124.4, 123.8, 120.8,
114.9, 114.7, 111.7, 95.9, 40.9, 21.2. MS (EI) m/z: 364 [M+].
Anal. calcd. for C21H20N2O2S: C, 69.20; H, 5.53; N, 7.69.
Found: C, 68.91; H, 5.77; N, 7.51.
124–126ꢀC; IR (KBr): 1698 (—CO2Me) cm
.
1H-NMR
(CDCl3, 300 MHz): d 8.63 (s, 1 H), 7.98 (q, J = 6.9 Hz, 2 H),
7.35 (t, J = 7.65 Hz, 1 H), 7.18–7.12 (m, 3 H), 3.84 (s, 3 H),
3.59 (s, 3 H). 13C-NMR (CDCl3, 75 MHz): d 167.9, 143.4,
141.5, 127.2, 126.3, 122.8, 122.7, 122.4, 120.6, 120.5, 119.8,
108.8, 107.9, 51.9, 29.1. MS (EI) m/z: 239 [M+]. Anal. calcd.
for C15H13NO2: C, 75.30; H, 5.48; N, 5.85. Found: C, 75.06;
H, 5.68; N, 5.56.
9-Phenylsulfonyl-2-(1-phenylsulfonyl-2-methyl-1H-indol-3-yl)-
3-nitro-9H-carbazole (19). This compound was obtained as
brown solid (0.22 g, 48%), mp: 232–234ꢀC; IR (KBr): 1508
1
and 1325 (—NO2), 1378 and 1180 (—SO2Ph) cmÀ1. H-NMR
(CDCl3, 300 MHz): d 8.64 (s, 1 H), 8.41 (d, J = 8.4 Hz, 1 H),
8.25 (t, J = 4.2 Hz, 2 H), 8.02 (d, J = 7.8 Hz, 1 H), 7.84–7.78
(m, 4 H), 7.68–7.31 (m, 9 H), 7.21 (d, J = 7.2 Hz, 1 H), 7.02
(d, J = 7.5 Hz, 1 H), 2.52 (s, 3 H). 13C-NMR (CDCl3, 75
MHz): d 139.8, 139.6, 139.1, 137.5, 136.3, 134.5, 133.8,
129.8, 129.4, 129.3, 126.8, 126.5, 126.2, 124.8, 124.7, 124.0,
120.7, 119.1, 118.7, 118.3, 117.2, 115.3, 114.9, 13.6. MS
(E)-Methyl 3-(1,2-dimethyl-1H-indol-3-yl)acrylate (10).
This compound was obtained as brown solid (0.21Àg1, 65%), mp:
130–132ꢀC; IR (KBr): 1726 (—CO2Me) cm
.
1H-NMR
(CDCl3, 300 MHz): d 7.89 (d, J = 15.9 Hz, 1 H), 7.80–7.77
(m, 1 H), 7.19–7.13 (m, 3 H), 6.33 (d, J = 15.6 Hz, 1 H),
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R. Sureshbabu and A. K. Mohanakrishnan
Vol 49
(EI) m/z: 621 [M+]. Anal. calcd. for C33H23N3O6S2: C, 63.75; H,
3.73; N, 6.76. Found: C, 63.43; H, 4.01; N, 6.54.
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1967; (b) Knölker, H.-J. Synlett 1992, 371; (c) Moody, C. J. Synlett
1994, 681; (d) Hibino, S.; Sugino, E. In Advances in Nitrogen
Heterocycles; Moody, C. J., Eds.; JAI Press, Greenwich (CT), 1995,
Vol. 1, pp 205–227; (e) Knölker, H.-J. In Transition Metals for
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1998, Vol. 1, pp 534–549; (f) Knölker, H.-J. Chem Soc Rev 1999,
28, 151.
Ethyl 2-(formylmethyl)-1-phenylsulfonyl-1H-indole-3-carboxylate
(24). This compound was obtained as thick brown liquid (0.40 g,
75%), IR (KBr): 1715 (—CO2Et), 1680 (—CHO), 1386 and 1178
1
(—SO2Ph) cmÀ1. H-NMR (CDCl3, 300 MHz): d 9.75 (s, 1 H),
8.11–8.05 (m, 2 H), 7.85 (d, J = 7.5 Hz, 2 H), 7.57 (t, J = 7.35
Hz, 1 H), 7.46 (t, J = 7.65 Hz, 2 H), 7.35–7.34 (m, 2 H), 4.81
(s, 2 H), 4.38 (q, J = 7.2 Hz, 2 H), 1.41 (t, J = 7.2 Hz, 3 H).
13C NMR (CDCl3, 75 MHz): d 196.1, 164.4, 139.7, 134.5, 129.5,
129.4, 127.5, 126.8, 126.3, 125.5, 124.6, 122.2, 114.2, 60.8, 29.7,
14.3. MS (EI) m/z: 371 [M+]. Anal. calcd. for C19H17NO5S: C,
61.44; H, 4.61; N, 3.77. Found: C, 61.15; H, 4.84; N, 3.52.
Ethyl 1,2-dimethyl-1H-indol-3-carboxylate (25). This
compound was obtained as colorless solid (0.19 g, 59%), mp:
96–98ꢀC; IR (KBr): 1695 (—CO2Et) cmÀ1. 1H-NMR (CDCl3, 300
MHz): d 8.14–8.10 (m, 1 H), 7.31–7.28 (m, 1 H), 7.24–7.21 (m, 2
H), 4.39 (q, J = 7.2 Hz, 2 H), 3.70 (s, 3 H), 2.77 (s, 3 H), 1.45 (t,
J = 7.2 Hz, 3 H). 13C-NMR (CDCl3, 75 MHz): d 166.2, 145.2,
136.5, 126.5, 121.9, 121.6, 121.4, 109.0, 103.9, 59.3, 29.5, 14.6,
11.8. MS (EI) m/z: 217 [M+]. Anal. calcd. for C13H15NO2: C,
71.87; H, 6.96; N, 6.45. Found: C, 71.55; H, 7.21; N, 6.23.
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Richett, M. E.; Sall, D. J.; Sayer, J. S. US Patent WO 2002050034,
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2-(3-Benzoyl-1-phenylsulfonyl-1H-indol-2-yl)acetaldehyde (26)
and (2-((dimethylamino)methyl)-1-phenylsulfonyl-1H-indol-3-yl)
(phenyl)methanone (27). This compound was obtained as thick
brown liquid, IR (KBr): 1685 (—CHO), 1660 and 1656 (—CO),
[10] (a) Blouin, N.; Michaud, A.; Wakim, S.; Boudreault, P. L. T.;
Leclerc, M.; Vercelli, B.; Zecchin, S.; Zotti, G. Macromol Chem Phys
2006, 207, 166; (b) Blouin, N.; Leclerc, M.; Vercelli, B.; Zecchin, S.;
Zotti, G. Macromol Chem Phys 2006, 207, 175.
1372 and 1164 (—SO2Ph) cmÀ1 1H-NMR (CDCl3, 300 MHz):
.
[11] (a) Choshi, T.; Sada, T.; Fujimoto, H.; Nagayama, C.; Sugino,
E.; Hibino, S. J Org Chem 1997, 62, 2535; (b) Brenna, E.; Fuganti, C.;
Serra, S. Tetrahedron 1998, 54, 1585; (c) Dötz, K. H.; Tomuschat, P.
Chem Soc Rev 1999, 28, 187.
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6905.
d 9.74 (s, 1 H), 8.24 (t, J = 4.65 Hz, 1 H), 8.06 (d, J = 8.4 Hz, 1 H),
7.90 (d, J = 7.5 Hz, 3 H), 7.77–7.69 (m, 4 H), 7.66–7.57 (m, 2 H),
7.52–7.41 (m, 8 H), 7.35–7.25 (m, 7 H), 7.17–7.10 (m, 2 H), 5.97
(d, J = 12.9 Hz, 1 H), 5.50 (d, J = 12.6 Hz, 1 H), 4.43 (s, 2 H), 2.51
(s, 6 H). 13C-NMR (CDCl3, 75 MHz): d 195.8, 150.5, 147.5, 139.1,
138.7, 138.4, 138.2, 136.7, 136.2, 135.7, 134.5, 133.8, 133.3, 131.4,
130.3, 129.6, 129.5, 128.8, 128.6, 128.0, 126.9, 125.3, 124.6, 124.1,
124.0, 122.8, 121.2, 120.0, 114.7, 114.3, 85.5, 41.7, 40.2, 29.7.
[13] Tois, J.; Vahermo, M.; Koskinen, A. Tetrahedron Lett 2005,
46, 735.
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Clement, J.; Balamurugan, R.; Sureshbabu, R.; Senthil Kumar, N. Tetrahedron
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2005, 46, 4045; (b) Sureshbabu, R.; Balamurugan, R.; Mohanakrishnan,
A. K. Tetrahedron 2009, 65, 3582.
Acknowledgments. The authors thank the University Grants
Commission (UGC), New Delhi (32-194/2006/SR) for financial
support. R.S thanks UGC, New Delhi for SRF fellowship.
The authors thank the Department of Science and Technology
(DST-FIST) for a 300 MHz NMR facility.
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1675; (b) Maehr, H.; Smallheer, J. M. J Org Chem 1981, 46, 1752.
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet