A Facile Synthesis of 3,4-Benzo-β-carbolines

Article abstract of DOI:10.1081/SCC-120030323

A convenient method for the synthesis 3,4-benzo-β-carbolines (10) from the corresponding N-phenylsulfonyl-3-bromo-N′-arylisogramines (5) via radical mediated cyclization methodology has been reported.

Full text of DOI:10.1081/SCC-120030323

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A Facile Synthesis of 3,4‐Benzo‐β‐carbolines
Sathananthan Kannadasan a & Panayencheri C. Srinivasan a
a Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai, 600
025, India
Published online: 21 Aug 2006.
To cite this article: Sathananthan Kannadasan & Panayencheri C. Srinivasan (2004) A Facile Synthesis of
3,4‐Benzo‐β‐carbolines, Synthetic Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 34:7, 1325-1335, DOI: 10.1081/SCC-120030323
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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 7, pp. 1325–1335, 2004
A Facile Synthesis of 3,4-Benzo-b-carbolines
*
Sathananthan Kannadasan and Panayencheri C. Srinivasan
Department of Organic Chemistry, University of Madras,
Chennai, India
ABSTRACT
A convenient method for the synthesis 3,4-benzo-b-carbolines (10) from
the corresponding N-phenylsulfonyl-3-bromo-N0-arylisogramines (5) via
radical mediated cyclization methodology has been reported.
Key Words: b-Carbolines; Cyclization; Debrominations; Heck reaction.
INTRODUCTION
b-Carbolines are currently of great interest because of their useful
biological activity. Many b-carbolines effectively bind to benzodiazepam
receptors in central nervous system.[1] b-Carbolines in which the pyridine por-
tion is fused in different positions have been the subject of research due to their
*
Correspondence: Panayencheri C. Srinivasan, Department of Organic Chemistry,
University of Madras, Guindy Campus, Chennai 600 025, India; Fax: 91-44-
2352494; E-mail: pancol2000@yahoo.co.in.
1325
DOI: 10.1081/SCC-120030323
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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Kannadasan and Srinivasan
pharmacological importance.[2,3] Traditionally, b-carbolines have been syn-
thesized either by Pictet–Spengler[4] or Bischler–Napieralski reactions[5]
from tryptamines. Synthesis of both b- and g-carbolines by the palladium
mediated iminoannulation of internal alkynes has been reported by Larock
and Zhang.[6] Synthesis of 3,4-benzo-b-carbolines in low yield by
palladium acetate mediated aryl–aryl coupling has been reported from our
lab.[7a] There are only a few reports on the generation of a radical at indole-
3-position.[7b,8] Synthesis of 1,2,3,4-terahydro-b-carbolines by Heck reaction
and radical cyclization was also reported from our lab.[7b] To the best of our
knowledge there is no report on the synthesis of 3,4-benzo-b-carboline
through a radical cyclization at indole-3-position. In continuation of our
studies[7] on the synthesis of b-carbolines from non-tryptamine precursors,
attempts were made to synthesize the same from N-phenylsulfonyl-3-
bromo-N0-arylisogramines (Sch. 1).
3-Bromo-2-methylindole 2 was converted into 3-bromo-N-phenylsulfonyl-2-
bromomethylindole 4 by published procedure.[7b] Treatment of the bromo
compound 4 with different anilines in DMF at room temperature afforded
the corresponding N0[N-phenylsulfonyl-3-bromoindol-2-ylmethyl]anilines
5a–5f. The structures of these compounds were confirmed by spectral data
(5a–5f) and XRD studies[9a,b] (5d and 5e).
Attempted Heck reaction of the compounds 5a–5c to 3,4-benzo-b-carbo-
lines using tetrakis(triphenylphosphine)palladium (5% molar equivalent) in
DMF–H2O (4.5 : 0.5) for 48 hr at 808C afforded only dehalogenated products
7a–7c. Since palladium mediated reactions are all oxidative reactions it was
thought that two bromines, namely one at indole-3-position and another at
ortho position of the aniline moiety, may be more suitable for carbon–carbon
bond formation. A search in the literature also indicated that palladium cata-
lyzed debromination with concomitant C–C bond formation of dibromo-
methylbenzenes to diarylethenes is known.[10] Hence compounds 5d and 5e
were treated with zerovalent palladium in DMF–H2O (0.5 mL) for 48 hr at
808C. This reaction also did not afford the expected b-carboline 6, instead
N-phenylsulfonyl-N0-(20-bromo)arylisogramines 8d, 8e, and completely
debrominated product namely N-phenylsulfonyl-N0-arylisogramines 7a and
7b were obtained. The structures of all these compounds were confirmed by
spectral data and XRD study (only in the case of 7c).[9c] The formation of 7
and 8 clearly indicates that debromination takes place at indole-3-position
first and then the ortho position in the N0-aryl moiety.[11] Thus, bromine
can be used to block indole-3-position in order to synthesize 2-substituted
indoles, as it can be removed very easily by zerovalent palladium complex
(Schs. 2 and 3).
Being unsuccessful with Heck methodology, we next intended to explore the
radical mediated C–C bond formation approach.[13] Radical cyclization continues

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Facile Synthesis of 3,4-Benzo-b-carbolines
1327
Scheme 1.
to form one of the central methodologies for the synthesis of natural products
containing heterocyclic rings.[14] Recently, Rosa et al. have reported an unusual
radical cyclization of benzyl anilines to phenanthridine ring system involving
an aryl–aryl coupling and subsequent aerial oxidation of the tetrahydrophenan-
thridine intermediate.[14] In similar lines attempted intramolecular radical cycliza-
tion of the compound 5a, 5b, and 5f using nBu3SnH in toluene led to a mixture of
N-phenylsulfonyl-3,4-benzo-b-carbolines 9a, 9b, and 9f, 3,4-benzo-b-carbolines
10a, 10b, and 10f and reduction products 7a, 7b, and 7f. The Bu3SnH mediated
desulfonylation of b-carbolines is a new feature observed in this reaction. A
search in the literature revealed that there is only one report, which involves
the desulfonylation of phenylsulfonamide[12] under radical condition. The struc-
tures of all the products were confirmed by spectral data (Sch. 4).

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Kannadasan and Srinivasan
Scheme 2.
EXPERIMENTAL
All melting points are uncorrected. IR spectra were recorded on FTIR-
1
8300 Shimadzu spectrophotometer. H and 13C-NMR spectra were recorded
on a Brucker-DPX 200 (200 MHz) or Brucker 300 MHz or on a Jeol-
GSX 400 (400 MHz) or on a Jeol FX 90Q (90 MHz) or on a Varian
Scheme 3.

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Facile Synthesis of 3,4-Benzo-b-carbolines
1329
Scheme 4.
400 MHz instruments with TMS as internal standard [chemical shift in (d)
ppm]. The mass spectra were recorded on a Jeol-JMS-DX 303 HF or Finnigan
MAT-8230 GC-Mass spectrometer. All chromatographic separations were
carried out using silica gel (ACME, 100–200 mesh). Thin layer chromatog-
raphy (TLC) was performed using glass plates coated with silica gel-G
(ACME samples) of 0.25 mm thickness. Spots were visualized using iodine
vapor. Reagents and solvents were purified by standard methods. Anhydrous
magnesium sulfate and sodium sulfate were used as the drying agents.
N-[3-Bromo-1-phenylsulfonylindol-2-ylmethyl]-p-toluidine 5a. A solu-
tion of 1-phenylsulfonyl-2-bromomethyl-3-bromoindole 4 (4.29 g, 10mmol)
and p-toluidine (2.14 g, 20mmol) in dry DMF (25 mL) containing finely
powdered K2CO3 (200mg) was stirred at room temperature for 12hr. Then
the reaction mixture was poured on ice (200g) and the precipitated solid was
filtered and washed with water. The crude product was dried in a CaCl2
desiccator under vacum and recrystallized from ethyl acetate–hexane (1: 9)
to give 5a as colorless crystals.
Yield: 3.64 g (80%); m.p.: 138–1408C; IR (KBr): 3400 (NH), 1362, 1175
(SO2) cm21; 1H NMR (90 MHz): d 2.22 (s, 3H, CH3), 4.50 (bs, 1H, NH), 4.77

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Kannadasan and Srinivasan
(s, 2H, CH2), 6.72–7.88 (m, 12H, Ar-H), 8.20 (d, 1H, indole-7-H); Mass m/z
(%): 456 (M þ 2, 14), 454 (Mþ, 15), 375 (4), 315 (8), 234 (22), 233 (30), 141
(14), 128 (25), 77 (100).
N-[3-Bromo-1-phenylsulfonylindol-2-ylmethyl]aniline 5b. A solution
of 1-phenylsulfonyl-2-bromomethyl-3-bromoindole 4 (4.29 g, 10 mmol) and
aniline (1.86 g, 20 mmol) in dry DMF (25 mL) containing finely powdered
K2CO3 (200 mg) was stirred at room temperature for 12 hr. Then the product
was isolated and purified as mentioned in the case of 5a.
Yield: 3.88 g, (88%); m.p.: 152–1548C, IR (KBr): 3380 (NH), 1367, 1178
1
(SO2) cm21; H NMR (90 MHz): d 4.52 (bs, 1H, NH), 4.78 (s, 2H, CH2),
6.67–8.02 (m, 13H, Ar-H), and 8.17 (d, IH, indole-7-H); Mass m/z (%):
442 (M þ 2, 55), 440 (Mþ, 52), 361 (27), 350 (72), 348 (63), 220 (52), 219
(100), 141 (10), 128 (37), 77 (80).
N-[3-Bromo-(1-phenylsulfonylindol-2-ylmethyl)]-N-methylaniline 5c.
5c was obtained from 1-phenylsulfonyl-2-bromomethyl-3-bromoindole 4
(4.29g, 10mmol) and N-methylaniline (2.14 g, 20mmol) by following the pre-
vious procedure.
Yield: 4.00 g (88%); m.p.: 100–1028C; IR (KBr): 1361, 1172 (SO2)
1
cm21: H NMR (200 MHz): d 2.29 (s, 3H, N–CH3), 4.82 (s, 2H, –CH2),
6.80–7.79 (m, 13H, Ar-H), 8.32 (d, 1H, J ¼ 8.32 Hz, indole-7-H); 13C
NMR: d 36.02, 47.57, 104.94, 114.75, 114.82, 118.61, 119.94, 124.06,
126.32, 126.57, 128.20, 128.76, 129.02, 133.20, 133.55, 136.43, 139.15,
149.94; DEPT-135: d 36.02 ("), 45.57 (#), 114.75, 114.83, 118.62, 119.95,
124.06, 126.33, 126.57, 128.77, 129.02, 133.55; Mass m/z (%): 456
(M þ 2, 14), 454 (Mþ, 15), 375 (38), 351 (18), 313 (15), 234 (56), 233
(100), 208 (40), 141(6), 129 (36), 128 (55), 77 (72).
N-[3-Bromo-1-phenylsulfonylindol-2-ylmethyl]-20-bromo-40-methylani-
line 5d. 5d was obtained from 1-phenylsulfonyl-2-bromomethyl-3-bromoindole
4 (0.858 g, 2 mmol) and 2-bromo-4-methylaniline (0.93 g, 5 mmol) by follow-
ing the previous procedure.
Yield: 0.658 g (62%); m.p.: 131–1338C; IR (KBr): 3410 (NH), 1370, 1178
(SO2) cm21; 1H NMR (200MHz): d 2.19 (s, 3H, –CH3), 4.83 (d, 2H, –CH2),
5.01 (m, 1H, –NH), 6.85–7.88 (m, 11H, Ar-H), 8.08 (d, 1H, indole-7-H); 13
C
NMR: d 19.96, 40.03, 104.17, 110.15, 112.42, 114.95, 119.99, 124.38, 126.29,
126.52, 128.09, 128.60, 128.93, 129.24, 132.90, 133.95, 134.74, 135.99, 138.21,
141.63; Mass m/z (%): 534 (M þ 2, 48), 532 (Mþ, 44), 455 (10), 453 (8),
393 (13), 391 (10), 350 (100), 348 (98), 374 (8), 233 (81), 218 (10), 207
(30), 184 (11), 128 (42), 77 (8).
N-[3-Bromo-1-phenylsulfonylindol-2-ylmethyl]-20-bromoaniline 5e.
5e was obtained from 1-phenylsulfonyl-2-bromomethyl-3-bromoindole 4
(0.858 g, 2 mmol) and 2-bromoaniline (0.860 g, 5 mmol) by following the
previous procedure.

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Facile Synthesis of 3,4-Benzo-b-carbolines
1331
Yield: 0.75 g (72%); m.p.:133–1358C; IR (KBr): 3371(NH), 1367, 1174
1
(SO2) cm21; H NMR (200 MHz): d 4.85–4.88 (d, 2H, –CH2), 5.16–5.28
(m, 1H, –NH), 6.52–7.78 (m, 12H, Ar-H), 8.06–8.09 (d, 1H, J ¼ 8.78 Hz,
indole-7-H).
N-[3-Bromo-1-phenylsulfonylindol-2ylmethyl]-40-isopropylaniline 5f. 5f
was obtained from 1-phenylsulfonyl-2-bromomethyl-3-bromoindole 4 (0.858 g,
2 mmol) and 4-isopropylaniline (0.670 g, 5 mmol) by following the previous
procedure.
Yield: 0.792, (82%); m.p.: 126–1288C; IR (KBr): 3404 (NH), 1364, 1174
1
(SO2) cm21; H NMR (400 MHz): d 1.19–1.21(d, 6H, –CH(CH3)2), 2.77–
2.82 (septet, 1H, CH(CH3)2), 4.46–4.50 (bs, 1H NH), 4.79 (s, 2H, –CH2),
6.71–7.77 (m, 12H, Ar-H), 8.10–8.12 (d, 1H, J ¼ 8.0 Hz, indole-7-H); 13C
NMR: d 24.18, 33.13, 40.36, 104.10, 113.69, 114.98, 119.99, 124.41,
126.21, 126.46, 127.06, 128.79, 129.27, 133.97, 135.45, 136.09, 138.31,
138.58, 144.85; Mass m/z (%): 484 (M þ 2, 53), 482 (Mþ, 56), 350 (26),
348 (24), 341 (16), 262 (31), 219 (100), 128 (67), 77(29).
General Procedure for the Synthesis of Isogramine 7
A mixture of 3-bromo-N0-arylisogramine 5 (1 mmol), tetrakistriphenyl-
phosphine palladium (115 mg, 10%mol equiv.), triethylamine (0.348 mL,
2.5 mmol), tetra-n-butylammonium hydrogen sulfate (0.339 g. 1 mmol), and
water (0.5 mL) was stirred under N2 at 808 for 48 hr. The reaction was moni-
tored by TLC. After the disappearance of the starting material, the reaction
mixture was poured over ice and extracted with chloroform (3 ꢀ 20 mL).
Then the extract was washed with water (3 ꢀ 50 mL) and dried over anhy-
drous MgSO4. After removal of the solvent, the residue was chromatographed
over silica gel to afford the corresponding N-arylisogramines 7.
N-[1-Phenylsulfonylindol-2-ylmethyl]-p-toluidine 7a. Yield: 0.30 g
1
(66%): m.p.: 90–928C; IR(KBr): 3417 (NH), 1367, 1176 (SO2) cm21; H
NMR (300 MHz): d 2.24 (s, 3H, –CH3), 4.29 (bs, 1H, –NH), 4.70 (s, 2H,
–CH2), 6.48–7.82 (m, 13H, Ar-H), 8.17 (d, 1H, J ¼ 8.32 Hz, indole-7-H);
13C NMR: d 20.39, 42.73, 110.73, 113.26, 113.60, 114.50, 120.80, 123.72,
124.52, 126.32, 129.37, 129.76, 133.86, 137.41, 138.94, 139.03, 144.87;
DEPT-135: d 20.32 ("), 42.73(#), 110.65, 113.17, 120.73, 123.65, 124.44,
126.24, 129.30, 129.67, 133.79; Mass m/z (%): 376 (Mþ), 270, 235, 233,
231, 218, 206, 141, 77. Anal. Calcd for C22H20N2O2S: C, 70.19; H, 5.35;
N, 7.44; Found: C, 70.52; H, 5.12; N, 7.32.
N-[1-phenylsulfonylindol-2-ylmethyl] aniline 7b. Yield: 0.217 g (60%);
1
m.p.: 110–1128C; IR(KBr): 3414(NH), 1372, 1172(SO2) cm21; H NMR
(200MHz): d 4.13–4.38 (bs, 1H, –NH), 4.70 (s, 2H, –CH2), 6.37–7.80

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Kannadasan and Srinivasan
(m, 14H, Ar-H), 8.11–8.15 (d, 1H, indole-7-H); HRMS: Mþ for C21H18N2O2S
Calcd: 362.1089; Found: 362.1087. Anal. Calcd for C21H18N2O2S: C, 69.59; H,
5.01; N, 7.73; Found: C, 69.84; H, 4.83; N, 7.52.
N-[1-Phenylsulfonylindol-2-ylmethyl]-N-methyl aniline 7c. Yield:
1
0.299 g (66%); m.p.: 124–1268C; IR (KBr): 1369, 1178 (SO2) cm21; H
NMR (300 MHz): d 3.04 (s, 3H, N–CH3), 4.85 (s, 2H, –CH2), 6.33(s, 1H
indole-3-H), 6.36 (d, 2H, J ¼ 9.99 Hz, Ar-H), 6.51–6.72 (m, 1H, Ar-H),
7.12–7.59 (in, 8H, Ar-H), 7.80–7.83 (d, 2H, J ¼ 7.6 Hz, Ar-H), 8.20–8.23
(d, 1H, J ¼ 8.26 Hz, indole-7-H); 13C NMR: d 38.60, 52.18, 109.72, 111.89,
114.32, 116.72, 120.61, 123.69, 124.30, 126.25, 129.04, 129.12, 129.40,
129.47, 133.88, 137.63, 137.68, 139.03, 148.67; Mass m/z (%): 376 (Mþ,
67), 270 (96), 235 (48), 233 (88), 129 (65), 128 (54), 77 (100).
N-[1-phenylsulfonylindol-2-ylmethyl]-20-bromo-40-methylaniline 8d.
Yield: 0.204 g (45%); m.p.: 124–1268C; IR (KBr): 3396 (NH), 1367,
1
1175 (SO2) cm21; H NMR (300 MHz): d 2.21 (s, 3H, –CH3), 4.78 (d, 2H,
–CH2), 4.88 (m, 1H, NH), 6.37–8.16(m. 13H, Ar-H); 13C NMR: d 19.99,
42.50, 109.74, 110.39, 111.64, 113.30, 113.98, 114.45, 120.80, 123.71,
124.58, 126.35, 128.93, 129.37, 132.88, 133.87, 138.37, 139.02, 141.72;
Mass m/z (%): 456 (M þ 2), 454 (Mþ), 315, 313, 234, 233, 218, 206, 141, 77.
N0-[1-Phenylsulfonylindol-2-ylmethyl]-20-bromoaniline 8e. Yield:
0.176 g (40%); m.p.: 130–1328C; IR (KBr): 3421 (NH), 1366, 1170 (SO2)
1
cm21; H NMR (200 MHz): d 4.77–4.80 (d, 2H, –CH2), 5.00–5.03 (t, 1H
NH), 6.45–7.80 (m, 13H, Ar-H), 8.11–8.15 (d, 1H, indole-7-H); 13C NMR:
d 42.22, 109.81, 110.45, 111.56, 114.42, 118.30, 120.78, 123.72, 124.60,
126.27, 128.35, 129.14, 129.33, 132.50, 133.82, 137.40, 138.05, 138.87,
143.98; DEPT-135: d 42.21(#), 110.45, 111.56, 114.42, 118.29, 120.78,
123.71, 124.59, 125.79, 126.27, 128.35, 129.33, 132.49, 133.82; HRMS
(Mþ): For C21H17BrN2O2S Calcd: 440.0194; Found: 440.0194.
General Procedure for Radical Cyclization of 5a, b, and f
To a solution of the appropriate bromo compound 5 (1mmol), tri-n-butylin
hydride (2 mmol) in dry toluene (50 mL), under reflux was added AIBN
(0.2 equiv.). The reaction was monitored by TLC. After 48hr, the solvent
was removed under reduced pressure. Then the residue was dissolved in ether
(40mL) and stirred with an aqueous solution of KF for 12hr. Then the organic
layer was separated, dried (MgSO4), and evaporated. The products were
separated by column chromatography (silica gel, ethyl acetate : hexane, 1 : 9).
1-Phenylsulfonyl-(6-methyl)-3,4-benzo-b-carboline 9a. Yield: 0.056 g
(15%); m.p.: 226–2288C; IR (KBr): 1377, 1180 (SO2) cm21 1H NMR
;
(400 MHz): d 2.64 (s, 3H, CH3), 7.26–7.85 (m, 8H, Ar-H), 8.16 (d, 1H,

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Facile Synthesis of 3,4-Benzo-b-carbolines
1333
J ¼ 8.8 Hz, C11–H), 8.35 (s, 1H, C7–H), 8.47 (d, 1H, J ¼ 8.32 Hz, Ar-H),
8.52 (d, 1H, J ¼ 8.8 Hz, Ar-H), 9.94 (s, 1H, C2–H); 13C NMR: d 22.11,
115.48, 122.48, 123.39, 123.48, 124.75, 125.44, 126.44, 128.70, 129.26,
130.00, 130.11, 131.66, 134.18, 137.43, 137.91, 138.43, 138.51, 143.45;
Mass m/z (%): 372 (Mþ, 20), 231 (100), 141 (6) 77 (35). Anal. Calcd for
C22H16N2O2S: C, 70.95; H, 4.33; N, 7.52; Found: C, 70.72; H, 4.52; N, 7.41.
1-Phenylsulfonyl-3,4-benzo-b-Carboline 9b. Yield: 0.090 g (25%);
1
m.p.: 230–2328C; IR (KBr): 1364, 1180 (SO2) cm21; H NMR (400 MHz):
d 7.19–7.79 (m, 10H Ar-H), 8.30 (d, 1H, C11–H), 8.46–8.58 (m, 2H,
Ar-H), 9.97 (s, 1H, C2–H); Mass m/z (%): 358 (Mþ, 88), 217 (100), 191
(11), 190 (37), 141 (5), 77 (33). Anal. Calcd for C21H14N2O2S: C, 70.37; H,
3.94; N, 7.82; Found: C, 70.02; H, 4.30; N, 7.88.
N-[1-Phenylsulfonylindol-2-ylmethyl]-40-isopropylaniline 7f. Yield:
65 mg, (16%), Sticky solid. m.p. could not be determined. IR (KBr): 3406
(NH), 2958, 1368, 1170 (SO2) cm21 1H NMR (90 MHz): d 1.05–1.08
;
(d, 6H, CH(CH3)2), 2.64–2.80 (septet, 1H, CH(CH3)2), 4.18 (bs, 1H, NH),
4.57 (s, 2H, –CH2), 6.33 (s, 1H, indole-3-H), 6.40–8.06 (m, 13H, Ar-H).
1-Phenylsulfonyl-6-isopropyl-3,4-benzo-b-carboline 9c. Yield: 0.056 g
(14%); m.p.: 192–1948C; IR (KBr): 1379, 1178 (SO2) cm21 1H NMR
;
(400 MHz): d 1.42–1.43 (d, 6H, –CH(CH3)2), 3.19–3.27 (septet, 1H,
–CH(CH3)2), 7.30–8.56 (m, 12H, Ar-H), 9.98 (s, 1H, C2–H); 13C NMR: d
24.33, 34.92, 115.90, 120.16, 122.32, 123.99, 125.27, 125.63, 126.80, 128.31,
128.72, 129.26, 129.66, 129.96, 134.62, 137.66, 138.16, 139.09, 149.37; Mass
m/z (%): 400 (Mþ, 81), 385 (6), 260 (48), 259 (100), 216 (8), 77 (19); Anal.
Calcd for C24H20N2O2S: C, 71.98; H, 5.03; N, 6.99; Found: C, 72.25; H, 4.82;
N, 6.82.
6-Methyl-3,4-benzo-b-carboline 10a. Yield: 0.093 g (40%); m.p.:
274–2768C; IR (KBr): 3452 (NH) cm21 1H NMR (400 MHz): d 3.01
;
(s, 3H, CH3), 7.91 (m, 1H, J ¼ 7.32 Hz, Ar-H), 8.01 (d, 1H, J ¼ 8.2 Hz, Ar-
H), 8.10 (m, 1H, J ¼ 7.8 Hz, Ar-H), 8.27 (d, 1H, J ¼ 8.32 Hz, C11–H), 8.59
(d, 1H, J ¼ 8.28 Hz, Ar-H), 9.09 (s, 1H, C7–H), 9.23 (d, 1H, J ¼ 8.32 Hz
Ar-H), 9.74 (s, 1H, C2–H), 12.68 (bs, 1H, D2O exchangeable, NH); 13C
NMR: d 21.48, 112.56, 119.25, 120.25, 121.29, 122.38, 123.14, 124.20,
126.70, 127.37, 129.33, 132.75, 136.87, 137.48, 139.52, 140.21; Mass m/z
(%): 232 (Mþ, 100), 231 (62), 77 (4); HRMS (Mþ): For C16H12N2 Calcd:
232.1000; Found: 232.0994.
3,4-Benzo-b-carboline 10b. Yield: 0.072 g (33%); m.p.: 238–2408C;
IR (KBr): 3410 (NH) cm21 1H NMR (200 MHz): 7.36–7.74 (m, 5H, Ar-H),
8.21–8.25 (d, 1H, J ¼ 7.94 Hz, C11–H), 8.54–8.58 (d, 1H, J ¼ 7.92 Hz,
C7–H), 8.70–8.73 (d, 1H, J ¼ 7.80 Hz, C4–H), 9.28 (s, 1H, C2–H), 11.68
(bs, 1H, D2O exchangeable, NH); 13C NMR: d 111.72, 113.83, 119.36,
120.85, 121.96, 122.23, 123.80, 124.27, 125.69, 125.95, 129.10, 137.76,

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1334
Kannadasan and Srinivasan
138.87; Mass m/z (%): 218 (Mþ, 100), 190 (16), 191 (7), 164(9), 109 (14);
HRMS (Mþ): For C15H10N2 Calcd: 218.0844; Found: 218.0848.
6-Isopropyl-3,4-benzo-b-carboline 10f. Yield: 0.122 g (47%); m.p.:
1
228–2308C; IR (KBr): 3407 (NH) cm21; H NMR (400 MHz): d 1.45–1.47
(d, 6H, –CH(CH3)2), 3.22–3.27(sep, 1H, –CH(CH3)2), 7.41–7.66 (m, 4H,
Ar-H), 8.22–8.25 (d, 1H, J ¼ 8.8 Hz, C11–H), 8.5 (s, 1H, Ar-H), 8.55–8.57
(d, 1H, J ¼ 8.0 Hz, Ar-H), 9.23 (s, 1H, C2–H), 9.92 (bs, 1H, –NH); 13C
NMR: d 24.14, 34.57, 112.26, 119.91, 120.75, 121.56, 122.35, 123.33,
124.85, 125.39, 127.01, 129.57, 132.63, 136.76, 139.66, 141.28, 148.00;
Mass m/z (%): 260 (Mþ, 91), 259 (14), 245 (100), 230 (7), 217 (6), 216
(6); HRMS (Mþ): For C18H6N2 Calcd: 260.1313; Found: 260.1306.
ACKNOWLEDGMENTS
The authors thank CSIR, New Delhi for financial support (SRF to SK) and
the UGC-SAP to this department from Government of India for instrument
grants.
REFERENCES
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Received in Japan November 3, 2003

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