A concise synthesis of novel naphtho[a]carbazoles and benzo[c]carbazoles

Article abstract of DOI:10.1016/j.tet.2006.01.012

Starting from simple indole precursors the synthesis of naphtho[a]carbazoles and benzo[c]carbazoles is described. Key steps include the use of the Suzuki-Miyaura reaction to afford 2- or 3-aryl substituted indoles, as well as a potassium t-butoxide and light assisted aromatic ring-forming reaction.

Full text of DOI:10.1016/j.tet.2006.01.012

Tetrahedron 62 (2006) 2820–2830
A concise synthesis of novel naphtho[a]carbazoles
and benzo[c]carbazoles
Rakhi Pathak, Johanna M. Nhlapo, Sameshnee Govender, Joseph P. Michael,
*
Willem A. L. van Otterlo and Charles B. de Koning
School of Chemistry, Molecular Sciences Institute, University of the Witwatersrand, Johannesburg, PO Wits 2050, South Africa
Received 28 October 2005; revised 28 November 2005; accepted 5 January 2006
Available online 30 January 2006
Abstract—Starting from simple indole precursors the synthesis of naphtho[a]carbazoles and benzo[c]carbazoles is described. Key steps
include the use of the Suzuki–Miyaura reaction to afford 2- or 3-aryl substituted indoles, as well as a potassium t-butoxide and light assisted
aromatic ring-forming reaction.
q 2006 Elsevier Ltd. All rights reserved.
1. Introduction
H
N
H
N
O
Indolocarbazoles such as rebeccamycin 1 and staurosporine
2 display a range of biological activities that make them
attractive compounds to synthetic and medicinal chemists.1–4
As a result, the synthesis of many analogues, for example,
3 and 4 and the benzo- and naphtho-fused carbazoles such as
5 and 6 (Fig. 1), have been described. Compound 3 has been
found to be a potent tyrosine kinase inhibitor of vascular
endothelial growth factor R2,5 while isogranulatimide 4 has
been described as an G2 checkpoint inhibitor.5a The naphtho-
and benzo-fused carbazoles (although rarely found in Nature)
are of interest owing to their potential as antitumour agents.
O
O
NH
OH
N
N
N
O
Cl
Cl
O
OH
MeO
NHMe
OMe
Rebeccamycin (1)
OH
Staurosporine (2)
H
NH
O
For example, the synthetic naphtho[a]carbazole6 5 is a
potential candidate for cancer treatment as a result of DNA
intercalative binding properties7 and the well-known indole/
naphthalene bioisotery,8 while benzo[c]carbazole 69 shows
promising profiles for intra-cyclin dependent kinase
selectivity. In general it has been found that modification
of the indolo[2,3-a]carbazole framework can lead to
products with very different useful pharmacological proper-
ties and biological activities.5
O
N
O
O
N
N
N
N
H
3
4
HO
HO
Me
N
O
In these laboratories, we have developed novel methodology
for the synthesis of benzo[a]carbazoles and pyrido[2,3-a]-
carbazoles10,11 by means of a novel light- and base-assisted
cyclization reaction to form a centrally-positioned aromatic
O
N
H
N
H
5
6
Keywords: Suzuki–Miyaura reaction; Carbazoles; Antitumour; Potassium
t-butoxide.
*
Corresponding author. Tel.: C27 11 717 6724; fax: C27 11 717 6749;
e-mail: dekoning@aurum.chem.wits.ac.za
Figure 1. Representative biologically active indolocarbazoles and naphtho-
and benzo-fused carbazoles.
0040–4020/$ - see front matter q 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.01.012

R. Pathak et al. / Tetrahedron 62 (2006) 2820–2830
2821
treated in the same manner as 1-bromo-2-methylnaphtha-
lene to afford 1-methyl-2-naphthylboronic acid 10b.
Boronic acid 10c was synthesised as described previously.15
Treatment of 10a–c with 9 under aqueous Suzuki–Miyaura
coupling reaction conditions afforded the desired biaryl
compounds 11, 12 and 13 in good yields (Scheme 1). It was
clear from the spectroscopic data that the desired products
had been formed. In particular, the presence of the aromatic
C-6 C-5
CHO
KOBut mediated
ring closure
R
R
N
Me
N
Me
7
8
Benzo[a]carbazoles
Figure 2. Retrosynthesis of benzo[c]carbazoles.
1
methyl protons in the range of d 2.2–2.5 in the H NMR
spectra were a good indication that the reaction had
proceeded. Exposure of each of these substrates (11, 12
and 13) to reaction conditions (KOBut, DMF, hn) that we
have developed for forming new aromatic rings gave the
desired naphtho-fused carbazoles 14, 15 and 16 in fair
to good yields (56–86%).11,15 Naphthocarbazole 16 could
also be oxidised with ceric ammonium nitrate to afford
quinone 17.16
ring (Fig. 2). For benzo[a]carbazoles 7, for example, the last
step entails the construction of the C-5/C-6 bond (i.e., 8/7)
by our novel ring-forming reaction.11
2. Results and discussion
As part of our ongoing programme we wished to extend the
methodology developed for the synthesis of benzo[a]carba-
zoles to the synthesis of naphtho[a]-fused carbazoles and
carbazoles containing rings fused onto the c-face. These
extensions are described in this paper.12
As depicted in the retrosynthesis in Figure 3, we planned to
extend this synthesis to benzo[c]carbazoles such as 18 from
indoles such as 19 or 20 containing a substituted aromatic
ring at the 3-position. Examination of the retrosynthesis
shows that a carbonyl-containing substituent is required
ortho to the biaryl linkage, either on the benzene ring or the
indole nucleus. In addition, either the benzene ring or the
indole nucleus must possess a methyl substituent at the
2-position. The biaryl linkage for both possible retro-
synthesis could be formed, as before, using Suzuki–Miyaura
coupling methodology.
As a starting point for this work we believed that treatment
of the readily available N-methyl-2-bromoindole-3-carbal-
dehyde 911 with a number of naphthaleneboronic acids, as
we had done previously for benzeneboronic acids would
provide easy access to naphtho[a]carbazoles. However,
since the desired naphthaleneboronic acids were not
commercially available, the initial task was to synthesize
them. Boronic acid 10a was prepared by treating 1-bromo-
2-methylnaphthalene13 with n-BuLi followed by the
addition of trimethyl borate and then hydrochloric acid.
The more challenging synthesis of boronic acid 10b
involved treatment of 1-methylindene with KOBut and
CHBr3 to give 2-bromo-1-methylnaphthalene,14 which was
As the first option we choose to attempt the synthesis using
the disconnection leading to the placement of the carbonyl
on the 2-position of the indole nucelus (i.e., 19, Fig. 4). We
believed that further disconnection would lead to a
3-bromoindole derivative such as 21. The synthesis of 21a
B(OH)2
OHC
ii
10a
i
85%
95%
N
Me
N
Me
CHO
Br
14
11
N
Me
9
B(OH)2
OHC
10b
i
ii
86%
56%
N
Me
N
Me
12
OMe
15
OHC
N
B(OH)2
OMe
OMe
O
OMe
10c
i
ii
iii
60%
86%
77%
N
N
Me
Me
Me
OMe
13
OMe
O
16
17
Scheme 1. Reagents and conditions: (i) 10 mol% Pd(PPh3)4, DME/EtOH, 2 M aq Na2CO3, reflux 48 h; (ii) KOBut, DMF, hn, 80 8C, 10 min; (iii) CAN,
THF, rt.

2822
R. Pathak et al. / Tetrahedron 62 (2006) 2820–2830
(HO)2B
R1
Br
R
O
R1
R
22
R
i
N
Me
N
N
SO2Ph
19a, R=H; R1=H or Me
19b, R=OMe; R1=H or Me
SO2Ph
23a, R=R1=H
23b, R=OMe; R1=H
23c, R=OMe; R1=Br
R
24a, R=H
R1
24a, R=OMe
N
Me
O
R
18a, R=H; R1=H or Me
18b, R=OMe, R1=H or Me
R
R
ii
R1
iii
N
N
Me
N
Me
H
20a, R=H; R1=H or Me
20b, R=OMe; R1=H or Me
26a, R=H
26b, R=OMe
25a, R=H
25b, R=OMe
Figure 3. Retrosynthesis of benzo[c]carbazoles.
R
R
Br
iv
Pd catalyst
R
CHO
N
R
N
O
R1
Me
Me
N
PG
(HO)2B
27a, R=H
28a, R=H
28b, R=OMe
N
Me
27b, R=OMe
21a, R=H
21b, R=OMe
22
19a, R=H; R1=H or Me
19b, R=OMe; R1=H or Me
Scheme 2. Reagents and conditions: (i) 10 mol% Pd(PPh3)4, DME, aq
K2CO3, reflux, 18 h, 24a, 100%; 24b, 99%; (ii) MeOH, K2CO3, reflux, 25a,
93%; 25b, 96%; (iii) (MeO)2SO2, THF, NaH, rt, 26a, 99%; 26b, 99%;
(iv) POCl3, DMF, reflux, 27a, 60%; 27b, 27%; (v) KOBut, DMF, hn, 80 8C,
10 min, no reaction.
Figure 4. Retrosynthesis of 19.
(PG]SO2Ph) has been described in the literature17 and the
toluene boronic acid 22 is commercially available and has
been made and used many times in our laboratories. We
thought that the carbonyl containing substituent at C-2 of
the indole nucleus could be introduced once the aromatic
ring had been placed at C-3 of the indole by means of a
Suzuki–Miyaura coupling reaction.
Vilsmeier–Haack reaction conditions to provide 27a and
27b in mediocre to poor yields of 60 and 27%, respectively.
We were now in a position to attempt the base mediated ring
closure reaction to hopefully yield the desired products 28a
and 28b. To our surprise all attempts at this reaction failed
to produce the desired products and the only detectable
products from this reaction were the result of deformylation
yielding 26a and 26b.18 Hence the alternative retrosynthesis
outlined in Figure 3 giving intermediates 20a and 20b was
pursued in which the positions of the carbonyl and methyl
substiuent were interchanged.
The synthesis commenced with the preparation of the
known compound 23a17 as well as its 5-methoxy analogue
23b. The analogue 23b was prepared by bromination of
5-methoxyindole followed by protection of the resulting
3-bromo-5-methoxyindole with phenylsulfonyl chloride to
afford 23b in 65% over two steps. If the steps were reversed
and 5-methoxy-1-(phenylsulfonyl)-1H-indole was treated
with bromine significant amounts of 23c were isolated
unless the reaction was done very carefully.
In order to achieve the synthesis of 20a–b, suitable
2-brominated indole precursors 29a and 29b were prepared
(Scheme 3). Exposure of 2-methylindole 30a to molecular
bromine followed by protection of the indole nitrogen by
N-methylation afforded 29a in good yield. The synthesis
of methoxyindole 29b was accomplished from 30b, but in
this case the bromination of 30b was accomplished with
Treatment of both 23a and 23b under Suzuki–Miyaura
reaction conditions with toluene boronic acid 22 provided
the desired 3-aryl substituted indoles 24a and 24b in good
yield (Scheme 2). In order to introduce the aldehyde
substituent at the 2-position of the indole nucleus the
phenylsulfonyl group on the indole nitrogen was removed
and replaced by a methyl in a two-step procedure.
Br
R
R
i, ii
N
Me
N
Me
The first step was accomplished with K2CO3 in MeOH to
give 25a and 25b and the second by exposure of the
free indole nitrogen to (MeO)2SO2 and NaH to afford 26a
and 26b. Attachment of the formyl group at C-2 was
achieved by treatment of 26a and 26b under classical
30a, R=H
30b, R=OMe
29a, R=H
29b, R=OMe
Scheme 3. Reagents and conditions: 30a/29a (i) Br2, DMF, rt, 99%; (ii)
(MeO)2SO2, NaH, THF, 18 h, 99%. 30b/29b (i) NBS, CH2Cl2, cat. SiO2,
30 min, 99%; (ii) (MeO)2SO2, NaH, THF, 48 h, 94%.

R. Pathak et al. / Tetrahedron 62 (2006) 2820–2830
2823
N-bromosuccinimide (NBS), as the use of molecular
bromine resulted in simultaneous bromination of the
electron-rich aromatic ring. Both 29a and 29b were unstable
and had to be used immediately in subsequent steps.
silica gel chromatography, and Macherey-Nagel Kieselgel
60 (particle size 0.040–0.063 mm) was used for preparative
flash chromatography. All solvents used for reactions and
chromatography were distilled prior to use. THF and Et2O
were freshly distilled from sodium benzophenone ketyl
under nitrogen.
Treatment of both 29a and 29b under non-aqueous Suzuki–
Miyaura coupling conditions with the commercially
available boronic acid 31 resulted in the formation of the
desired biaryl compounds 20a and 20b in good yields
(Scheme 4). Exposure of 20a and 20b to potassium
t-butoxide in the presence of light gave the desired
benzo[c]carbazoles 18a and 18b in good yield. Clear
evidence for the formation of the products was provided
by spectroscopy. For example, in the 1H NMR spectrum of
18a an aromatic methyl at d 2.79 was present and it was
noted that both the acetyl methyl and the methyl at the
2-position of the indole nucleus of the starting material 20a
were no longer observed.
3.1.1. 1-Bromo-2-methylnaphthalene. A solution of Br2
(0.40 mL, 7.8 mmol) in acetic acid (2 mL) was added
dropwise to a solution of 2-methylnaphthalene (1.01 g,
7.10 mmol) and anhydrous KOAc (0.75 g, 7.8 mmol) in
AcOH (2 mL). After the mixture had been stirred for 15 min
it was added to CH2Cl2 (20 mL) and the solution was
washed with saturated aq NaHCO3 (30 mL) and H2O
(20 mL). The residue obtained upon evaporation was
purified by column chromatography (20% EtOAc–hexane)
to obtain the product, 1-bromo-2-methylnaphthalene
(1.43 g, 92%) as a clear oil. The spectral data agreed with
that described in the literature.13
3.1.2. 2-Bromo-1-methylnaphthalene. KOBut (2.10 g,
18.6 mmol) was stirred in 25 mL anhydrous Et2O under
N2 atmosphere. Redistilled 1-methylindene (2.01 g,
15.5 mmol) was added dropwise to yield an orange slurry.
Freshly distilled CHBr3 (4.85 g, 19.6 mmol) was then added
dropwise over a period of 35 min. The slurry became pink,
then red and finally a deep red-violet with precipitation of
solid material. The reaction mixture was periodically cooled
to 20 8C while it was stirred for 2.5 h. The mixture was
then quenched with water (50 mL) and extracted with Et2O
(3!50 mL) followed by brine. The mixture was filtered and
dried with MgSO4 to give brown oil. The oil was slurred in
37.5 mL of absolute EtOH and 0.50 g of KOH and heated at
reflux for 30 min. Hexane (50 mL) was added and the
mixture was heated for 30 min and filtered. The mixture was
then rinsed with hexane (3!50 mL) and the solution was
finally evaporated on a rotary evaporator. The crude
material was then purified by column chromatography
(5–20% EtOAc–hexane) to give the product, 2-bromo-1-
methylnaphthalene (3.8 g, 38%) as a yellow oil. The 1H and
13C NMR spectral data agreed with that described in the
literature.14
(HO)2B
O
Br
R
O
31
R
i
N
Me
N
Me
29a, R=H
29b, R=OMe
20a, R=H
20b, R=OMe
R
ii
N
Me
18a, R=H
18b, R=OMe
Scheme 4. Reagents and conditions: (i) 20 mol% Pd(PPh3)4, DMF, K3PO4,
100 8C, 65 h, 20a, 83%; 20b, 80%; (ii) KOBut, DMF, hn, 80 8C, 10 min,
18a, 71%; 18b, 70%.
In conclusion, we have been able to show that both [a]-fused
naphtho- and [c]-fused benzocarbazoles can be synthesised
from simple indole precursors using our well developed
aromatic ring-forming reaction.
3.1.3. 2-Methyl-1-naphthylboronic acid 10a. n-BuLi
(1.2 M, 3.9 mL, 4.7 mmol) was added dropwise to a
solution of 1-bromo-2-methylnaphthalene (1.01 g,
4.57 mmol) in THF (30 mL) at K78 8C. The reaction
mixture was stirred for 30 min at K78 8C, then B(OMe)3
(1.39 g, 1.50 mL, 13.4 mmol) was added. The resulting
mixture was stirred at K78 8C for a further 30 min and then
allowed to warm to rt. The reaction mixture was acidified
with aq 10% HCl solution and extracted with Et2O
(3!30 mL). The organic layer was then dried with
MgSO4 and concentrated under vacuum to afford an off-
white crystalline material, 2-methyl-1-naphthylboronic acid
10a (0.74 g, 87%), which was used without further
purification or characterization.
3. Experimental
3.1. General
1H and 13C NMR spectra were recorded either on a Bruker
1
ADVANCE 300 (300.132 MHz for H, 75.473 for 13C), a
Bruker DRX-400 (400.132 MHz for 1H, 100.625 for 13C) or
a Bruker AC-200 (200.13 MHz for 1H, 50.32 for 13C)
spectrometer at the frequency indicated. J-values are given
in Hz. Infra-red spectra were recorded on either a Bruker
IFS 25 Fourier Transform spectrometer, or on a Bruker
Vector 22 Fourier Transform spectrometer. Mass spectra
were recorded on a Kratos MS 9/50, VG 70E MS or a VG 70
SEQ mass spectrometer. Macherey-Nagel Kieselgel 60
(particle size 0.063–0.200 mm) was used for conventional
3.1.4. 1-Methyl-2-naphthylboronic acid 10b. n-BuLi
(1.4 M, 2.1 mL, 2.9 mmol) was added dropwise to a
solution of 2-bromo-1-methylnaphthalene (0.50 g,
2.3 mmol) in THF (15 mL) at K78 8C. The reaction mixture
was then treated as described above and B(OMe)3

2824
R. Pathak et al. / Tetrahedron 62 (2006) 2820–2830
(0.70 g, 0.75 mL, 6.7 mmol) was added. An off-white
crystalline material, 1-methyl-2-naphthylboronic acid 10b
(0.39 g, 93%) was produced, which was used without
further purification or characterization.
128.1 (Ar-CH), 129.2 (Ar-CH), 132.9 (Ar-C), 134.3 (Ar-C),
135.9 (Ar-C), 137.8 (Ar-C), 152.2 (Ar-C), 186.6 (CHO);
MS m/z 299 (MC, 78%), 284 (100), 282 (74), 254 (24);
HRMS calcd for C21H17NO: 299.1310, found: 299.1309.
3.1.5. 1,4-Dimethoxy-3-methyl-2-naphthylboronic acid
10c. 2-Bromo-1,4-dimethoxy-3-methylnaphthalene was
prepared according to Ref. 19. This was then treated as
described above to afford the desired boronic acid 10c.15
3.2.3. 1-Methyl-2-(1,4-dimethoxy-2-methyl-3-naphthyl)-
1H-indole-3-carbaldehyde 13. The product 13 was isolated
as a yellow solid (0.224 g, 60%) from 9 (0.247 g,
1.04 mmol) and 10c (0.359 g, 1.46 mmol). Mp 147–
148 8C; IR nmax /cmK1 1655 (C]O) and 1593 (ArC]C);
dH (300 MHz; CDCl3; Me4Si) 2.16 (3H, s, ArCH3), 3.55 and
3.60 (each 3H, s, 2!OCH3), 3.95 (3H, s, NCH3), 7.37–7.47
(3H, m, 3!Ar-H), 7.57–7.67 (2H, m, 2!Ar-H), 8.13–8.20
(2H, m, 2!Ar-H), 8.42–8.45 (1H, m, Ar-H), 9.73 (1H, s,
CHO); dC (75 MHz; CDCl3), 13.8 (ArCH3), 30.4 (NCH3),
61.5 and 62.0 (2!OCH3), 109.9 (Ar-CH), 115.8 (Ar-C),
119.4 (Ar-C), 122.0 (Ar-CH), 122.4 (Ar-CH), 122.9 (Ar-
CH), 123.0 (Ar-CH), 123.7 (Ar-CH), 125.2 (Ar-C), 126.3
(Ar-CH), 126.3 (Ar-C), 127.1 (Ar-C), 127.7 (Ar-CH), 129.9
(Ar-C), 137.6 (Ar-C), 147.2 (Ar-C), 150.4 (Ar-C), 152.2
(Ar-C), 185.6 (CHO); MS m/z 360 (MCC1, 25%) 359
(MC, 100), 344 (23), 329 (20), 328 (68) and 285 (17);
HRMS calcd for C23H21NO3: 359.1521, found: 259.1535.
3.2. Representative procedure for the Suzuki coupling
reactions
3.2.1. 1-Methyl-2-(2-methyl-1-naphthyl)-1H-indole-3-
carbaldehyde 11. A solution of 2-bromo-1-methyl-1H-
indole-3-carbaldehyde 9 (0.100 g, 0.420 mmol) in DME
(2 mL) was deoxygenated by passing N2 through the
mixture for 5 min. The deoxygenated mixture was added
to Pd(PPh3)4 (10 mol%, 0.048 g, 0.040 mmol) and stirred
under N2 for 10 min at rt. A solution of 2-methyl-1-
naphthylboronic acid 10a (0.110 g, 0.591 mmol) in EtOH
(1.5 mL) was deoxygenated and added to the reaction
mixture. The mixture was stirred for a further 10 min. A
deoxygenated 2 M aq Na2CO3 solution (3.0 mL, 6.0 mmol)
was added and the reaction mixture was stirred at rt for
5 min before being heated at reflux for 2 days. The mixture
was cooled to rt and quenched with H2O (20 mL). The
organic material was extracted with CH2Cl2 (3!30 mL)
and the solvent was evaporated under reduced pressure. The
crude product was subjected to column chromatography
(2–10% EtOAc–hexane) to afford 1-methyl-2-(2-methyl-1-
naphthyl)-1H-indole-3-carbaldehyde 11 as an off-white
solid (0.120 g, 95%). Mp 146–147 8C; nmax/cmK1 1655
(C]O), 1579 (ArC]C), 1501, 1466, 1444 and 1421; dH
(300 MHz; CDCl3; Me4Si) 2.28 (3H, s, ArCH3), 3.42 (3H, s,
NCH3), 7.23 (1H, m, Ar-H), 7.35–7.51 (6H, m, 6!Ar-H),
7.91 (1H, d, JZ8.0 Hz, Ar-H), 7.96 (1H, d, JZ8.5 Hz, Ar-
H), 8.48 (1H, m, Ar-H) and 9.45 (1H, s, CHO); dC (75 MHz;
CDCl3) 20.5 (ArCH3), 30.2 (NCH3), 109.8 (Ar-CH), 116.4
(Ar-C), 122.3 (Ar-CH), 123.3 (Ar-CH), 123.8 (Ar-CH),
124.4 (Ar-C), 125.0 (Ar-CH), 125.3 (Ar-C), 125.7 (Ar-CH),
127.4 (Ar-CH), 128.1 (2!Ar-CH), 130.2 (Ar-CH), 131.7
(Ar-C), 133.6 (Ar-C), 137.3 (Ar-C), 137.6 (Ar-C) and 149.4
(Ar-C), 186.0 (CHO); MS m/z 299 (MC, 100%), 284 (38),
282 (55), 254 (19) and 127 (14); HRMS calcd for
C21H17NO: 299.1310, found: 299.1307.
3.3. Representative procedure for the ring-forming
reactions
3.3.1. 13-Methyl-13H-naphtho[1,2-a]carbazole 14.
KOBut (0.06 g, 0.53 mmol) was added to 1-methyl-2-
(2-methyl-1-naphthyl)-1H-indole-3-carbaldehyde
11
(0.045 g, 0.15 mmol) dissolved in dry DMF (6 cm3) and
was heated under N2 atmosphere at 80 8C while being
irradiated with a high pressure mercury lamp through a
quartz filter for 10 min. The reaction mixture was quenched
with H2O (50 mL) and extracted with Et2O (3!50 mL).
The organic layer was dried with MgSO4 and filtered. It was
then evaporated and subjected to column chromatography
(10–20% EtOAc–hexane) to afford the product 14 (0.034 g,
85%) as an off-white solid. Mp 113–115 8C; IR nmax/cmK1
1616 (ArC]C), 1559 and 1527; dH (300 MHz; CDCl3;
Me4Si) 3.78 (3H, s, NCH3), 7.31–7.34 (1H, m, Ar-H), 7.49–
7.61 (4H, m, 4!Ar-H), 7.70 (1H, d, JZ8.1 Hz, Ar-H), 7.74
(1H, d, JZ8.7 Hz, Ar-H), 7.86 (1H, d, JZ8.7 Hz, Ar-H),
7.93 (1H, d, JZ7.9 Hz, Ar-H), 8.15 (1H, d, JZ7.7 Hz,
Ar-H), 8.22 (1H, d, JZ8.1 Hz, Ar-H) and 8.66 (1H, d, JZ
8.1 Hz, Ar-H); dC (75 MHz; CDCl3) 37.6 (NCH3), 111.2
(Ar-CH), 118.2 (Ar-C), 119.3 (Ar-CH), 120.0 (Ar-CH),
120.6 (Ar-CH), 121.3 (Ar-CH), 123.9 (Ar-C), 124.8 (Ar-C),
125.1 (Ar-CH), 125.7 (2!Ar-CH), 125.9 (Ar-CH), 127.7
(2!Ar-CH), 127.9 (Ar-CH), 128.5 (Ar-C), 132.1 (Ar-C),
132.4 (Ar-C), 140.0 (Ar-C) and 145.9 (Ar-C); MS m/z 281
(MC, 100%), 266 (18), 265 (19) and 141 (9); HRMS calcd
for C21H12N: 281.1204, found: 281.1203.
The following compounds were prepared in a similar
manner.
3.2.2. 1-Methyl-2-(1-methyl-2-naphthyl)-1H-indole-3-
carbaldehyde 12. The product 12 was isolated as an off-
white solid (0.162 g, 86%) from 9 (0.150 g, 0.630 mmol)
and 10b (0.164 g, 0.882 mmol). Mp 184–186 8C; IR nmax
/
cmK1 1652 (C]O), 1610, 1579 and 1528 (ArC]C); dH
(300 MHz; CDCl3; Me4Si) 2.52 (3H, s, ArCH3), 3.53 (3H, s,
NCH3), 7.35–7.43 (4H, m, 4!Ar-H), 7.61–7.67 (2H, m,
2!Ar-H), 7.83 (1H, d, JZ8.4 Hz, Ar-H), 7.93–7.96 (1H,
m, Ar-H), 8.11–8.14 (1H, m, Ar-H), 8.43–8.46 (1H, m, Ar-
H), 9.61 (1H, s, CHO); dC (75 MHz; CDCl3) 17.0 (ArCH3),
31.0 (NCH3), 110.2 (Ar-CH), 116.6 (Ar-C), 122.6 (Ar-CH),
123.7 (Ar-CH), 124.3 (Ar-CH), 125.0 (Ar-CH), 125.6
(Ar-C), 125.9 (Ar-C), 126.9 (Ar-CH), 127.5 (2!Ar-CH),
The following compounds were prepared in a similar
manner.
3.3.2. 11-Methyl-11H-naphtho[2,1-a]carbazole 15. The
product 15 was isolated as an off-white solid (0.045 g, 56%)
from 12 (0.085 g, 0.28 mmol). Mp 213–216 8C; IR nmax
(CHCl3)/cmK1 1617 and 1572 (ArC]C), 1466, 1437 and
1407; dH (300 MHz; CDCl3; Me4Si) 4.43 (3H, s, NCH3),
7.30–7.35 (1H, m, Ar-H), 7.50–7.71 (4H, m, 4!Ar-H), 7.86

R. Pathak et al. / Tetrahedron 62 (2006) 2820–2830
2825
(1H, d, JZ9.2 Hz, Ar-H), 7.94 (1H, d, JZ7.6 Hz, Ar-H),
8.20 (1H, d, JZ7.8 Hz, Ar-H), 8.35 (1H, d, JZ8.7 Hz,
Ar-H), 8.60 (1H, d, JZ8.7 Hz, Ar-H), 8.71 (1H, d, JZ
9.2 Hz, Ar-H) and 8.82 (1H, d, JZ8.3 Hz, Ar-H); dC
(75 MHz; CDCl3) 34.4 (NCH3), 109.0 (Ar-CH), 114.8
(Ar-CH), 119.2 (Ar-CH), 119.5 (Ar-CH), 119.8 (Ar-CH),
120.7 (Ar-C), 121.0 (Ar-CH), 122.8 (Ar-C), 123.5 (Ar-CH),
125.3 (Ar-CH), 125.8 (Ar-CH), 126.1 (Ar-CH), 126.7
(Ar-CH), 128.4 (Ar-CH), 129.7 (Ar-C), 131.1 (Ar-C),
131.2 (Ar-C), 137.0 (Ar-C) and 141.6 (Ar-C), (one
quaternary C not observed); MS m/z 281 (MC, 100%),
266 (22), 252 (3) and 140 (2); HRMS calcd for C21H15N:
281.1204, found: 281.1209.
poured into a saturated solution of aq NaHCO3 (80 mL).
The resulting two layers were separated, and the organic
layer successively washed with aq Na2S2O3 (60 mL), H2O
(60 mL), brine (60 mL) and then dried with MgSO4 mixed
with charcoal. The solvent was removed under reduced
pressure and the crude residue was purified by chromato-
graphy (20% EtOAc–hexane) to afford the product 23a
(2.58 g, 99%) as light orange crystals. Mp 125–126 8C, lit.
(125–127 8C);17 dH (400 MHz; CDCl3; MeSi4) 7.29–7.57
(6H, m, 6!Ar-H), 7.63 (1H, s, 2-H), 7.87–7.91 (2H, m, 2!
Ar-H) and 7.99 (1H, d, JZ8.3 Hz, Ar-H); dC (50 MHz;
CDCl3) 99.8 (Ar-C), 113.6 (Ar-CH), 120.0 (Ar-CH),
124.0 (Ar-CH), 124.7 (Ar-CH), 125.8 (Ar-CH), 126.8
(2!Ar-CH), 129.3 (Ar-C), 129.4 (2!Ar-CH), 134.1
(Ar-CH), 134.2 (Ar-C) and 137.8 (Ar-C).17
3.3.3. 5,13-Dimethoxy-12-methyl-12H-naptho[2,3-a]-
carbazole 16. The product 16 was isolated as a pale yellow
solid (0.050 g, 81%) from 13 (0.065 g, 0.18 mmol). Mp
133–135 8C; IR nmax /cmK1 1605 (ArC]C); dH (300 MHz;
CDCl3; Me4Si) 3.81 (3H, s, NCH3), 4.17 and 4.25 (each 3H,
s, 2!OCH3), 7.33–7.38 (1H, m, Ar-H), 7.49–7.58 (3H, m,
3!Ar-H), 7.63 (1H, d, JZ8.2 Hz, Ar-H), 8.09 (2H, s, 2!
Ar-H), 8.14 (1H, d, JZ7.8 Hz, Ar-H), 8.33–8.37 (1H, m,
Ar-H) and 8.42–8.45 (1H, m, Ar-H); dC (75 MHz; CDCl3)
37.2 (NCH3), 62.0 and 63.0 (2!OCH3), 110.7 (Ar-CH),
115.0 (Ar-CH), 115.4 (Ar-C), 119.1 (Ar-C), 119.3 (Ar-CH),
119.4 (Ar-CH), 120.3 (Ar-CH), 122.4 (Ar-CH), 122.7
(Ar-CH), 124.0 (Ar-C), 124.7 (Ar-CH), 124.8 (Ar-C),
125.4 (Ar-CH), 125.5 (Ar-CH), 125.6 (Ar-C), 125.7
(Ar-C), 137.9 (Ar-C), 143.3 (Ar-C), 147.1 (Ar-C) and
148.7 (Ar-C); MS m/z 342 (MCC1, 34%), 341 (MC, 80),
327 (20), 326 (100), 312 (16), 311 (42), 310 (44), 282 (8),
170 (14), 163 (10), 155 (14), 149 (18) and 69 (13); HRMS
calcd for C23H19NO2: 341.1416, found: 341.1411.
3.3.6. 3-Bromo-5-methoxy-1-(phenylsulfonyl)-1H-indole
23b. 5-Methoxyindole (200 mg, 1.36 mmol) was dissolved
in DMF (5 mL). To the resulting solution Br2 (219 mg,
0.070 mL, 1.37 mmol) dissolved in DMF (5 mL) was added
dropwise within a few minutes at rt while stirring. The end
point of the reaction was easily detectable by the appearance
of the halogen colour (light brown). The reaction mixture
was then poured onto ice and H2O (50 mL) containing 0.5%
NH3 and 0.1% sodium metabisulphite. The white precipitate
formed was then filtered, washed with cold H2O and dried.
Recrystallization was carried out from EtOH/H2O to give
fluffy white crystals (256 mg, 83%) of 3-bromo-5-methoxy-
1H-indole. To an ice-cold mixture of powdered NaOH
(55 mg, 1.37 mmol) and tetrabutylammonium bromide
(3.7 mg, 0.015 mmol) in dry CH2Cl2 (3 mL) under N2 was
added solid 3-bromo-5-methoxy-1H-indole (100 mg,
0.442 mmol) followed by the addition of phenylsulfonyl
chloride (94 mg, 0.068 mL, 0.53 mmol). The reaction
mixture was then stirred vigorously at rt for 2 h. The
white precipitate that formed was filtered off and the solid
was purified by silica gel column chromatography (20%
EtOAc–hexane) to afford the product 23b (126 mg, 78%) as
a white solid. Mp 131–133 8C; IR nmax (CHCl3)/cmK1 1615
and 1583 (ArC]C), 1475, 1447, 1435 and 1375; dH
(300 MHz; CDCl3; Me4Si) 3.84 (3H, s, OMe), 6.89 (1H, d,
JZ1.2 Hz, 4-H), 6.98 (1H, dd, JZ6.8, 1.2 Hz, 6-H), 7.42–
7.46 (2H, m, 2!Ar-H), 7.53–7.58 (1H, m, 2!Ar-H), 7.58
(1H, s, 2-H), 7.84–7.86 (2H, m, Ar-H) and 7.89 (1H, d, JZ
6.8 Hz, 7-H); dC (75 MHz; CDCl3) 55.7 (OMe), 99.8 (3-C),
101.9 (Ar-CH), 114.7 (Ar-CH), 115.4 (Ar-CH), 125.4 (Ar-
CH), 126.8 (2!Ar-CH), 128.8 (Ar-C), 129.3 (2!Ar-CH),
130.8 (Ar-C), 134.0 (Ar-CH), 137.8 (Ar-C) and 157.1 (5-C);
MS m/z 367 (MC, 64%), 365 (64), 226 (98), 224 (100), 211
(14), 209 (14), 183 (21), 181 (16), 178 (25), 124 (21), 102
(16), 81 (15), 77 (51) and 69 (36); HRMS calcd for
C15H12Br79NO3S: 364.9721, found: 364.9722.
3.3.4. 12-Methyl-5H-naphtho[2,3-a]carbazole-5,13-
(12H)-dione 17. Carbazole 16 (10 mg, 0.0029 mmol) in
THF was stirred together with cerium(IV) ammonium nitrate
(7 mg, 0.013 mmol) at rt for 30 min. Water was added to the
reaction mixture and the organic material was extracted into
Et2O (3!20 mL). The combined organic layers were dried
with MgSO4 and filtered. The organic solvent was then
evaporated and subjected to column chromatography (20–
40% EtOAc–hexane) to afford the product 17 as an orange
solid (7 mg, 77%). mp193–195 8C; IR nmax/cmK1 1644
(C]O), 1621 and 1594 (ArC]C); dH (300 MHz; CDCl3;
Me4Si) 4.03 (3H, s, NCH3), 7.32–7.37 (1H, m, Ar-H),
7.54–7.63 (2H, m, 2!Ar-H), 7.74–7.83 (2H, m, 2!Ar-H),
8.13 (1H, d, JZ7.8 Hz, Ar-H), 8.24–8.30 (3H, m, 3!Ar-H)
and 8.40 (1H, d, JZ8.0 Hz, Ar-H); dC (75 MHz; CDCl3) 36.0
(NCH3), 110.5 (Ar-CH), 119.0 (Ar-CH), 120.8 (Ar-CH),
120.9 (Ar-CH), 121.9 (Ar-C), 125.2 (Ar-CH), 126.7 (Ar-CH),
126.8 (Ar-CH), 128.3 (Ar-CH), 131.1 (Ar-C), 132.6 (Ar-C),
133.2 (Ar-C), 133.4 (Ar-CH), 133.9 (Ar-CH), 135.4 (Ar-C),
140.0 (Ar-C), 143.2 (Ar-C), 145.5 (Ar-C), 183.7 (C]O) and
191.8 (C]O); MS m/z 312 (MC, 22%), 311 (92), 310 (100),
297 (33), 282 (8), 254 (11), 155 (5) and 127 (7); HRMS calcd
for C21H13O2N: 311.0946, found: 311.0946.
3.3.7. 3,4-Dibromo-5-methoxy-1-(phenylsulfonyl)-1H-
indole 23c. 5-Methoxy-1-(phenylsulfonyl)-1H-indole
(2.00 g, 6.97 mmol) was dissolved in CCl4 (60 mL). To
the resulting solution, Br2 (1.22 g, 0.40 mL, 7.67 mmol) was
added dropwise. The red reaction mixture was then stirred at
rt for 4.5 h, and then poured into saturated solution of aq
NaHCO3 (80 mL). The resulting two layers were separated,
and the organic layer successively washed with aq Na2S2O3
(60 mL), water (60 mL), brine (60 mL) and then dried with
MgSO4 mixed with charcoal. The solvent was removed
3.3.5. 3-Bromo-1-(phenylsulfonyl)-1H-indole 23a. 1-
(Phenylsulfonyl)-1H-indole (2.00 g, 7.77 mmol) was dis-
solved in CH2Cl2 (60 mL). To the resulting solution, Br2
(1.37 g, 0.440 mL, 8.55 mmol) was added dropwise. The
red reaction mixture was then stirred at rt for 4.5 h, and then

2826
R. Pathak et al. / Tetrahedron 62 (2006) 2820–2830
under reduced pressure and the crude residue was purified
by chromatography (10% EtOAc–hexane) to afford the
product 23c (2.53 g, 82%) as orange crystals. Mp 129 8C; IR
nmax/cmK1 1600, 1582, 1561 (ArC]C), 1462, 1449, 1415
and 1375; dH (400 MHz; CDCl3; Me4Si) 3.91 (3H, s,
OCH3), 6.98 (1H, d, JZ9.1 Hz, 6-H), 7.44–7.49 (2H, m,
2!Ar-H), 7.56–7.60 (1H, m, Ar-H), 7.67 (1H, s, 2-H),
7.83–7.87 (2H, m, 2!Ar-H) and 7.94 (1H, d, JZ9.1 Hz,
7-H); dC (100 MHz; CDCl3) 57.7 (OCH3), 98.9 (3-C)a,
103.9 (4-C)a, 111.6 (Ar-CH), 113.5 (Ar-CH), 127.2 (2!
Ar-CH), 127.5 (Ar-C), 128.5 (Ar-CH), 129.8 (Ar-C), 129.9
(2!Ar-CH), 134.7 (Ar-CH), 137.8 (Ar-C) and 153.6 (5-C);
MS m/z 347 (MC, 100%), 445, (68), 443 (36), 415 (15), 306
(46), 304 (100), 302 (51), 289 (26), 265 (21), 261 (24), 256
(35), 214 (26), 132 (22), 130 (22), 97 (21), 85 (17), 83 (30),
81 (38), 77 (53), 73 (40), 71 (29), 69 (82), 67 (27), 60 (32),
(Ar-CH), 123.5 (Ar-CH), 123.7 (Ar-C), 124.0 (Ar-CH),
124.9 (Ar-CH), 125.8 (Ar-CH), 126.7 (2!Ar-CH), 127.9
(Ar-CH), 129.2 (2!Ar-CH), 130.4 (Ar-CH), 130.5 (Ar-
CH), 130.7 (Ar-C), 131.8 (Ar-C), 133.8 (Ar-CH), 135.0
(Ar-C), 136.8 (Ar-C) and 138.1 (Ar-C); MS m/z 348 (MCC
1, 15%), 347 (MC, 61), 207 (18), 206 (100), 204 (18), 178
(31), 103 (4) and 77 (10); HRMS calcd for C21H17NO2S
347.0980, found: 347.0980.
3.3.10. 5-Methoxy-3-(2-methylphenyl)-1-(phenylsul-
fonyl)-1H-indole 24b. A solution of 3-bromo-5-methoxy-
1-(phenylsulfonyl)-1H-indole 23b (2.21 g, 6.04 mmol) in
DME (48 mL) was deoxygenated by passing through it a
fast stream of N2 for 5 min. This deoxygenated solution was
added to Pd(PPh3)4 (10%, 0.70 g, 0.60 mmol) and stirred
under an atmosphere of N2 at rt for 10 min. A solution of
2-bromophenylboronic acid 22 (1.23 g, 9.07 mmol) in 96%
ethanol (16 mL) was also deoxygenated and added to
mixture. The mixture was stirred for another 10 min
followed by the addition of deoxygenated aq 2 M Na2CO3
(26 mL, 51.3 mmol) solution. The resulting mixture
was further stirred at rt under N2 for 10 min. The mixture
was then heated at reflux for 18 h under N2. The mixture was
cooled to rt and quenched with H2O (80 mL). The organic
material was extracted into CH2Cl2 (3!80 mL), the
combined organic extracts dried with MgSO4 and the
solvent evaporated under reduced pressure. The crude
residue was purified with column chromatography (20%
EtOAc–hexane) to afford the product 24b (2.25 g, 99%) as
white crystals. Mp 127–128 8C (MeOH); IR nmax/cmK1
1616, 1558 (ArC]C), 1540, 1521, 1506, 1458 and 1365; dH
(400 MHz; CDCl3; Me4Si) 2.18 (3H, s, ArCH3), 3.73 (3H, s,
OCH3), 6.72 (1H, d, JZ2.5 Hz, 4-H), 6.96 (1H, dd, JZ8.7,
2.5 Hz, 6-H), 7.26–7.32 (4H, m, 4!Ar-H), 7.41–7.47 (3H,
m, 3!Ar-H), 7.51–7.53 (1H, m, Ar-H), 7.86–7.90 (2H, m,
2!Ar-H) and 7.94–7.97 (1H, dd, JZ9.0, 0.4 Hz, Ar-H); dC
(50 MHz; CDCl3) 20.3 (ArCH3), 55.7 (OCH3), 102.9
(Ar-CH), 114.0 (Ar-CH), 114.8 (Ar-CH), 124.0 (Ar-C),
124.9 (Ar-CH), 125.8 (Ar-CH), 126.7 (2!Ar-CH), 128.0
(Ar-CH), 129.2 (2!Ar-CH), 129.7 (Ar-C), 130.4 (Ar-CH),
130.5 (Ar-CH), 131.8 (Ar-C), 131.9 (Ar-C), 133.7 (Ar-CH),
136.9 (Ar-C), 138.1 (Ar-C) and 156.8 (5-C); MS m/z 378
(MCC1, 25%), 377 (MC, 100), 237 (15), 236 (80), 205
(14), 204 (19), 192 (9), 165 (10) and 77 (10); HRMS calcd
for C22H19NO3S 377.1086, found: MC377.1078.
57 (53), 56 (20), 55 (74), 51 (20), 43 (80), 41 (86) and 39
(19); HRMS calcd for C15H Br2NO3S 442.8826, found:
79
11
442.8944. The position of the bromine atom was determined
by NOE spectroscopy.
3.3.8. 2-Methylphenylboronic acid 22. 1-Bromo-2-
methylbenzene (5.00 g, 3.50 mL, 29.3 mmol) was dissolved
in THF (30 mL) and cooled to K78 8C. n-Butyllithium
(25.1 mL, 32.2 mmol) was added dropwise and the resulting
white suspension was stirred at K78 8C under an
atmosphere of nitrogen for 30 min. After this time trimethyl
borate (9.11 g, 9.8 mL, 37.7 mmol) was added dropwise and
the reaction mixture stirred for a further 30 min at K78 8C.
The reaction mixture was then gradually warmed to rt and
acidified with 10% aq HCl and extracted with CH2Cl2 (3!
60 mL) and the combined organic extracts were dried with
MgSO4. The inorganic solids were filtered off and the
solvent removed under reduced pressure to afford white
crystalline material 23 in quantitative yield. The product
was then used without any further purification or
characterisation.20
3.3.9. 3-(2-Methylphenyl)-1-(phenylsulfonyl)-1H-indole
24a. A solution of 3-bromo-1-(phenylsulfonyl)-1H-indole
23a (0.25 g, 0.74 mmol) in DME (6 mL) was deoxygenated
by passing through it a fast stream of N2 for 5 min. This
deoxygenated solution was added to Pd(PPh3)4 (10%,
86 mg, 0.074 mmol) and stirred under an atmosphere of
N2 at rt for 10 min. A solution of 2-bromophenylboronic
acid 22 (0.15 g, 1.1 mmol) in 96% EtOH (2 mL) was also
deoxygenated and added to mixture. The mixture was
stirred for another 10 min followed by the addition of a
deoxygenated aq Na2CO3 solution (3.2 mL, 6.3 mmol). The
resulting mixture was further stirred at rt under N2 for
10 min. The mixture was then heated at reflux for 18 h under
N2. The mixture was cooled to rt and quenched with H2O
(20 mL). The organic material was extracted into CH2Cl2
(3!30 mL), the combined organic extracts dried with
MgSO4 and the solvent evaporated under reduced pressure.
The crude residue was purified with column chromatog-
raphy (20% EtOAc–hexane) to afford the product 24a
(0.26 g, 100%) as a light orange oil. IR nmax/cmK1 1523
(ArC]C), 1425 and 1374; dH (400 MHz; CDCl3; Me4Si)
2.19 (3H, s, ArCH3), 7.19–7.41 (7H, m, 7!Ar-H), 7.41–
7.46 (2H, m, 2!Ar-H), 7.51–7.54 (2H, m, 2!Ar-H), 7.90–
7.93 (2H, m, 2!Ar-H) and 8.05–8.08 (1H, m, Ar-H); dC
(100 MHz; CDCl3) 20.3 (ArCH3), 113.8 (Ar-CH), 120.7
3.3.11. 3-(2-Methylphenyl)-1H-indole 25a. 3-(2-Methyl-
phenyl)-1-(phenylsulfonyl)-1H-indole 24a (0.028 g,
0.080 mmol) was dissolved in MeOH (20 mL) at rt under
N2. K2CO3 (1.78 g, 12.9 mmol) was added to the solution
and the reaction mixture heated to reflux under an
atmosphere of N2 for 18 h. The mixture was allowed to
cool to rt, filtered and the filtrate concentrated under reduced
pressure. H2O (15 mL) was added to the crude material and
slowly acidified to pH 2–4 with aq 10% HCl. The aq portion
was saturated with solid NaCl and the organic material
extracted with CH2Cl2 (3!20 mL). The combined organic
extracts were washed with H2O (2!20 mL), brine (2!
20 mL), dried with MgSO4 and concentrated under reduced
pressure. The residue was subjected to column chromatog-
raphy (20% EtOAc–hexane) to afford product 25a (0.16 g,
93%) as a light yellow oil. IR nmax/cmK1 3487 (NH)
and 1523 (ArC]C); dH (200 MHz; CDCl3; MeSi4) 2.31

R. Pathak et al. / Tetrahedron 62 (2006) 2820–2830
2827
(3H, s, ArCH3), 7.09–7.33 (6H, m, 6!Ar-H), 7.37–7.44
(2H, m, 2!Ar-H), 7.52 (1H, dd, JZ7.9, 1.1 Hz, Ar-H) and
8.09 (1H, br s, N-H); dC (100 MHz; CDCl3) 20.7 (ArCH3),
111.2 (Ar-CH), 117.4 (Ar-C), 119.9 (Ar-CH), 120.1
(Ar-CH), 122.1 (Ar-CH), 122.7 (Ar-CH), 125.6 (Ar-CH),
126.7 (Ar-CH), 127.1 (Ar-C), 130.3 (Ar-CH), 130.9
(Ar-CH), 134.4 (Ar-C), 135.8 (Ar-C) and 136.8 (Ar-C);
MS m/z 208 (MCC1, 16%), 207 (MC, 100), 206 (63), 204
(16), 178 (15) and 102 (10); HRMS calcd for C15H13N
207.1048, found: 207.1050.
3.3.14. 5-Methoxy-1-methyl-3-(2-methylphenyl)-1H-
indole 26b. To a solution of 5-methoxy-3-(2-methyl-
phenyl)-1H-indole 25b (175 mg, 0.737 mmol) in THF
(10 mL) was added dimethyl sulfate (0.14 g, 0.10 mL,
1.1 mmol) followed by NaH (50% in oil, 0.043 g,
1.8 mmol). The resulting mixture was stirred at rt under a
constant flow of N2 for 18 h. The reaction was quenched
with H2O (15 mL), extracted with Et2O (3!30 mL),
combined organic layers dried with MgSO4 and concen-
trated under reduced pressure. The crude product was
purified by column chromatography (20% EtOAc–hexane)
to afford 26b (183 mg, 99%); IR nmax/cmK1 1618 and 1603
(ArC]C), 1576, 1559 and 1542; dH (400 MHz; CDCl3;
MeSi4) 2.33 (3H, s, ArCH3), 3.78 (3H, s, NCH3)a, 3.79 (3H,
s, OCH3)a, 6.90–6.94 (2H, m, 2!Ar-H), 6.99 (1H, s, 2-H),
7.22–7.25 (3H, m, 3!Ar-H), 7.30–7.32 (1H, m, Ar-H) and
7.39–7.41 (1H, m, Ar-H); dC (100 MHz; CDCl3) 20.7
(ArCH3), 32.9 (NCH3), 55.9 (OCH3), 101.7 (Ar-CH), 110.1
(Ar-CH), 112.1 (Ar-CH), 115.5 (Ar-C), 125.6 (Ar-CH),
126.5 (Ar-CH), 127.8 (Ar-C), 128.1 (Ar-CH), 130.4
(Ar-CH), 130.7 (Ar-CH), 132.1 (Ar-C), 134.6 (Ar-C),
136.7 (Ar-C) and 154.3 (5-C); MS m/z 252 (MCC1,
27%), 251 (MC, 100%) 236 (54), 218 (15), 208 (9) and 165
(8); HRMS calcd for C17H17NO 251.1310, found: 251.1296.
3.3.12. 5-Methoxy-3-(2-methylphenyl)-1H-indole 25b.
5-Methoxy-3-(2-methylphenyl)-1-(phenylsulfonyl)-1H-
indole 24b (0.30 mg, 0.80 mmol) was dissolved in MeOH
(30 mL) at rt under N2. K2CO3 (1.76 g, 12.7 mmol) was
added to the solution and the reaction mixture heated to
reflux under an atmosphere of N2 for 18 h. The mixture was
allowed to cool to rt, filtered and the filtrate concentrated
under reduced pressure. H2O (30 mL) was added to the
crude material and slowly acidified to pH 2–4 with 10%
HCl. The aq portion was saturated with solid NaCl and
extracted with CH2Cl2 (3!30 mL). The combined organic
extracts were washed with H2O (2!30 mL), brine (2!
30 mL), dried with MgSO4 and concentrated under reduced
pressure. The residue was subjected to column chromato-
graphy (20% EtOAc–hexane) to afford product 25b (0.18 g,
96%) as a light yellow oil. IR nmax/cmK1 3417 br (NH) 1624
and 1603 (ArC]C), 1582, 1545, 1481, 1455 and 1439; dH
(400 MHz; CDCl3; Me4Si) 2.32 (3H, s, ArCH3), 3.78 (3H, s,
OCH3), 6.89 (1H, dd, JZ8.7, 2.5 Hz, 6-H), 6.93 (1H, d, JZ
2.5 Hz, Ar-H), 7.11 (1H, d, JZ2.5 Hz, Ar-H), 7.25–7.34
(4H, m, 4!Ar-H), 7.40–7.42 (1H, m, ArH) and 8.09 (1H, br
s, N-H); dC (100 MHz; CDCl3) 20.7 (ArCH3), 55.9 (OCH3),
101.6 (Ar-CH), 111.9 (Ar-CH), 112.6 (Ar-CH), 117.3
(Ar-C), 123.5 (Ar-CH), 125.6 (Ar-CH), 126.7 (Ar-CH),
127.5 (Ar-C), 130.3 (Ar-CH), 130.8 (Ar-CH), 131.0 (Ar-C),
134.6 (Ar-C), 136.9 (Ar-C) and 154.4 (5-C); MS m/z 238
(MCC1, 17%), 237 (MC, 100), 222 (51), 206 (12), 194 (17)
and 165 (11); HRMS calcd for C16H15NO 237.1155, found:
237.1164.
3.3.15.
1-Methyl-3-(2-methylphenyl)-1H-indole-2-
carbaldehyde 27a. DMF (0.30 g, 0.30 mL, 4.1 mmol) was
added to POCl3 (0.42 g, 0.25 mL, 2.71 mmol) at 0 8C under
an atmosphere of N2. The resulting salt was treated with a
solution of 1-methyl-3-(2-methylphenyl)-1H-indole 26a
(300 mg, 1.36 mmol) in toluene (6 mL). The resulting
reaction mixture was heated at reflux for 42 h under N2
atmosphere. The reaction mixture was then cooled to
rt, quenched with water and the excess POCl3 neutralised
with Na2CO3. The crude product was extracted with CH2Cl2
(3!50 mL), the combined organic extracts dried with
MgSO4, and evaporated under reduced pressure. The crude
material was purified by column chromatography (20%
EtOAc–hexane) to afford product 27a (202 mg, 60%) as a
light brown oil. IR nmax/cmK1 1709 (C]O) and 1608
(ArC]C); dH (200 MHz; CDCl3; MeSi4) 2.18 (3H, s,
ArCH3), 4.16 (3H, s, NCH3), 7.11–7.15 (1H, m, Ar-H),
7.23–7.44 (7H, m, 7!Ar-H) and 9.66 (1H, s, CHO); dC
(100 MHz; CDCl3) 20.9 (ArCH3), 32.2 (NCH3), 110.8
(Ar-CH), 121.3 (Ar-CH), 122.9 (Ar-CH), 125.9 (Ar-CH),
126.7 (Ar-C), 127.7 (Ar-CH), 128.7 (Ar-CH), 130.7
(Ar-CH), 131.7 (Ar-C), 131.8 (Ar-C), 131.9 (Ar-C), 132.5
(Ar-CH), 138.2 (Ar-C), 140.0 (Ar-C) and 184.2 (CHO); MS
m/z 250 (MCC1, 18%), 249 (MC, 100), 234 (32), 232 (69),
220 (18), 217 (24) and 204 (18); HRMS calcd for C17H15NO
249.1154, found: 249.1158.
3.3.13. 1-Methyl-3-(2-methylphenyl)-1H-indole 26a. To a
solution of 3-(2-methylphenyl)-1H-indole 25a (0.45 g,
2.2 mmol) in THF (10 mL) was added dimethyl sulfate
(1.8 mol equiv, 0.50 g, 0.37 mL, 3.9 mmol) followed by
NaH (50% in oil, 0.12 g, 5.2 mmol). The resulting mixture
was stirred at rt under a constant flow of N2 for 18 h. The
reaction was quenched with H2O (20 mL), extracted with
Et2O (3!50 mL), combined organic layers dried with
MgSO4 and concentrated under reduced pressure. The
crude product was purified by column chromatography
(20% EtOAc–hexane) to afford 26a (481 mg, 99%); IR
nmax/cmK1 1653, 1634 and 1616 (ArC]C); dH (200 MHz;
CDCl3; MeSi4) 2.32 (3H, s, ArCH3), 3.78 (3H, s, NCH3),
7.00 (1H, s, 2-H), 7.07–7.26 (1H, m, Ar-H), 7.28–7.41 (6H,
m, 6!Ar-H) and 7.49–7.54 (1H, m, Ar-H); dC (50 MHz;
CDCl3) 20.8 (ArCH3), 32.7 (NCH3), 109.3 (Ar-CH), 115.9
(Ar-C), 119.4 (Ar-CH), 120.2 (Ar-CH), 121.7 (Ar-CH),
125.6 (Ar-CH), 126.5 (Ar-CH), 127.5 (Ar-CH), 130.3
(Ar-CH), 130.8 (Ar-CH), 132.2 (Ar-C), 134.5 (Ar-C) and
136.7 (Ar-C), (one quaternary C not observed); MS m/z 221
(MC, 100%), 220 (57), 204 (13) and 178 (9); HRMS calcd
for C16H15N 221.1204, found: 221.1199.
3.3.16. 5-Methoxy-1-methyl-3-(2-methylphenyl)-1H-
indole-2-carbaldehyde 27b. DMF (0.124 g, 0.13 mL,
1.70 mmol) was added to POCl3 (0.17 g, 0.10 mL,
1.1 mmol) at 0 8C under an atmosphere of N2. The resulting
salt was treated with a solution of 5-methoxy-1-methyl-3-
(2-methylphenyl)-1H-indole 26b (140 mg, 0.557 mmol) in
toluene (4 mL). The reaction mixture was then heated to
reflux for 42 h under N2 atmosphere. The reaction mixture
was then cooled to rt, quenched with water and excess
POCl3 neutralised with Na2CO3. The crude product was
extracted into CH2Cl2 (3!30 mL), the combined organic

2828
R. Pathak et al. / Tetrahedron 62 (2006) 2820–2830
extracts dried with MgSO4, and evaporated under reduced
pressure. The crude material was purified by column
chromatography (20% EtOAc–hexane) to afford product
27b (156 mg, 27%) as a brown oil. IR nmax/cmK1 1716
(C]O), 1654 and 1617 (ArC]C); dH (400 MHz; CDCl3,
MeSi4) 2.23 (3H, s, ArCH3), 3.78 (3H, s, NCH3), 4.17 (3H,
s, OCH3), 6.75 (1H, d, JZ2.3 Hz, 4-H) and 7.15 (1H, dd,
JZ9.1, 2.3 Hz, 6-H), 7.28–7.41 (5H, m, 5!Ar-H) and 9.63
(1H, s, CHO); dC (50 MHz; CDCl3) 20.6 (ArCH3), 33.1
(NCH3), 56.0 (OCH3), 100.6 (Ar-CH), 109.9 (Ar-CH),
116.1 (Ar-C), 120.9 (Ar-C), 125.8 (Ar-CH), 127.0 (Ar-CH),
130.5 (Ar-CH), 130.6 (Ar-CH), 131.6 (Ar-C), 132.7 (Ar-
CH), 133.0 (Ar-C), 133.8 (Ar-C), 136.8 (Ar-C), 156.5 (5-C)
and 190.4 (CHO); MS m/z 280 (MCC1, 30%), 279 (MC,
100), 264 (19), 262 (38), 247 (16), 218 (9), 206 (10), 204
(9), 192 (6), 165 (9) and 152 (6); HRMS calcd for
C18H17NO2 279.1259, found: 279.1253.
was sealed tightly and heated at 100 8C for 65 h. After this
time the reaction mixture was cooled and followed by the
addition of saturated solution of brine (10 mL). The reaction
mixture was extracted with Et2O (4!15 mL), and the
organic extracts were combined and concentrated under
reduced pressure. Purification of the residue by column
chromatography (20% EtOAc–hexane) afforded the biaryl
compound 20a as a yellow-brown oil (0.19 g, 83%); IR
nmax/cmK1 1683 (C]O) and 1614 and 1596 (ArC]C),
1558, 1541 and 1472; dH (400 MHz; CDCl3; MeSi4) 1.88
(3H, s, 2-CH3), 2.26 (3H, s, CH3CO), 3.74 (3H, s, NCH3),
7.32 (1H, d, JZ8.2 Hz, Ar-H), 7.18–7.24 (1H, m, Ar-H),
7.25–7.31 (1H, m, Ar-H), 7.37–7.44 (3H, m, 3!Ar-H) and
7.50–7.55 (1H, m, Ar-H), 7.63 (1H, d, JZ7.7 Hz, Ar-H); dC
(100 MHz; CDCl3) 10.9 (2-CH3), 29.3 (NCH3), 29.8
(CH3CO), 108.8 (Ar-CH), 112.9 (Ar-C), 118.6 (Ar-CH),
120.0 (Ar-CH), 121.5 (Ar-CH), 126.8 (Ar-CH), 127.4
(Ar-C), 128.0 (Ar-CH), 130.8 (Ar-CH), 132.1 (Ar-CH),
133.8 (Ar-C), 134.6 (Ar-C), 136.7 (Ar-C), 142.2 (Ar-C) and
205.0 (CH3CO); MS m/z 264 (MCC1, 20%), 263 (MC,
100), 262 (11), 249 (14), 248 (68), 245 (16), 234 (10), 233
(21), 218 (14), 204 (16) and 144 (10); HRMS calcd for
C18H17NO: 263.1310, found: MC263.1312.
3.3.17.
1-[2-(1,2-Dimethyl-1H-indol-3-yl)phenyl]-
ethanone 20a. (a) 2-Methyl-1H-indole (1.00 g,
7.62 mmol) was dissolved in DMF (7.5 mL). A solution of
Br2 (1.22 g, 0.390 mL, 7.62 mmol) in DMF (7.5 mL) was
added to the reaction mixture and the resulting solution was
stirred at rt under N2 atmosphere for 4 h. After this time the
reaction mixture was poured into an ice-cold mixture of
H2O (10 mL), a 25% aq NH3 solution (10 mL) and an aq
solution of NaHSO3 (10 mL). The resulting precipitate was
then dissolved in CH2Cl2 (20 mL). The organic layer was
sequentially washed with H2O (20 mL), aq NaCl (20 mL),
dried with MgSO4 and concentrated in vacuo. The residue
was then loaded on a silica gel column and eluted with 20%
EtOAc–hexane to afford the desired product 3-bromo-2-
methyl-1H-indole (1.61 g, 100%) as an off-white solid. dH
(200 MHz; CDCl3; MeSi4) 2.40 (3H, s, 2-CH3), 7.13–7.23
(3H, m, 3!Ar-H), 7.45–7.47 (1H, m, 7-H) and 8.0 (1H, br s,
NH); dC (50 MHz; CDCl3) 12.2 (2-CH3), 100.3 (3-C), 112.0
(7-C), 121.5 (Ar-CH), 121.9 (Ar-CH), 122.3 (Ar-CH), 128.2
(Ar-C), 130.3 (Ar-C) and 136.7 (Ar-C).21
3.3.18. 1-[2-(5-Methoxy-1,2-dimethyl-1H-indol-3yl)-
phenyl]ethanone 20b. (a) 5-Methoxy-2-methyl-1H-indole
(600 mg, 3.72 mmol) was dissolved in CH2Cl2 (4 mL). To
the resulting solution was added a small amount (ca.
100 mg) of silica gel followed by N-bromosuccinimide
(660 mg, 3.72 mmol). The resulting mixture was stirred at
rt for 30 min under an atmosphere of N2. The reaction
was quenched with H2O (30 mL), extracted with CH2Cl2
(3!50 mL), the combined organic extracts were dried with
MgSO4 and then concentrated under reduced pressure. The
residue was purified by column chromatography (20%
EtOAc–hexane) to afford 3-bromo-5-methoxy-2-methyl-
1H-indole (870 mg, 99%). dH (400 MHz; CDCl3; MeSi4)
2.38 (3H, s, 2-CH3), 3.87 (3H, s, OCH3), 6.80 (1H, dd, JZ
8.7, 2.1 Hz, 6-H), 6.91 (1H, d, JZ1.5 Hz, 4-H), 7.12 (1H, d,
JZ8.7 Hz, 7-H) and 7.89 (1H, br s, NH); dC (100 MHz;
CDCl3) 12.4 (2-CH3), 55.8 (OCH3), 90.0 (3-C), 100.0 (6-C),
111.5 (Ar-CH), 112.3 (Ar-CH), 128.1 (Ar-C), 129.6 (Ar-C),
133.1 (Ar-C) and 154.7 (5-C).
(b) To the intermediate 3-bromo-2-methyl-1H-indole
(1.60 g, 7.60 mmol) in THF (50 mL) was added dimethyl
sulfate (1.44 g, 1.08 mL, 11.4 mmol) followed by sodium
hydride (50% in oil, 0.44 g, 18 mmol). The resulting
mixture was stirred at rt under a constant flow of N2 for
18 h. The reaction was quenched with H2O (35 mL),
extracted with Et2O (3!40 mL), the combined organic
layers were dried with MgSO4 and concentrated under
reduced pressure. The crude product was purified by column
chromatography (20% EtOAc–hexane) to afford 30a22
(1.68 g, 99%) which was used immediately in the next
reaction. dH (200 MHz; CDCl3; MeSi4) 2.36 (3H, s, 2-CH3),
3.59 (3H, s, NCH3), 7.12–7.20 (3H, m, 3!Ar-H) and 7.45–
7.49 (1H, m, Ar-H); dC (50 MHz; CDCl3) 12.4 (2-CH3),
33.5 (NCH3), 102.4 (3-C), 112.9 (Ar-CH), 121.9 (Ar-CH),
122.3 (Ar-CH), 123.2 (Ar-CH), 128.7 (Ar-C), 130.8 (Ar-C)
and 137.2 (Ar-C).
(b) To a solution of 3-bromo-5-methoxy-2-methyl-1H-
indole (350 mg, 1.46 mmol) in THF (10 mL) was added
dimethyl sulfate (0.28 g, 0.21 mL, 2.2 mmol) followed by
NaH (50% in oil, 0.084 g, 2.2 mmol). The resulting mixture
was stirred at rt under a constant flow of N2 for 18 h. The
reaction was quenched with H2O (20 mL), extracted with
Et2O (3!20 mL), and the combined organic layers dried
with MgSO4 and concentrated under reduced pressure. The
crude product was purified by column chromatography
(20% EtOAc–hexane) to afford 30b (350 mg, 94%) which
was used as soon as possible in the next reaction. dH
(400 MHz; CDCl3; MeSi4) 2.38 (3H, s, 2-CH3), 3.71 (3H, s,
NCH3), 3.87 (3H, s, OCH3), 6.82 (1H, dd, JZ8.8, 2.4 Hz,
6-H), 6.91 (1H, d, JZ2.2 Hz, 4-H) and 7.13 (1H, d, JZ
8.8 Hz, 7-H); dC (100 MHz; CDCl3) 11.5 (2-CH3), 30.3
(NCH3), 55.8 (OCH3), 88.5 (3-C), 99.9 (4-C), 109.8
(Ar-CH), 111.9 (Ar-CH), 127.1 (Ar-CH), 131.2 (Ar-C),
134.5 (Ar-C) and 154.5 (5-C).
(c) Boronic acid 31 (0.29 g, 1.7 mmol) was dissolved in
DMF (1.5 mL) and O2 removed from the solution by three
freeze-thaw cycles. 3-Bromo-1,2-dimethyl-1H-indole 30a
(0.20 g, 0.89 mmol), K3PO4 (0.57 g, 2.7 mmol) and
Pd(PPh3)4 (20 mol%, 0.21 g, 0.18 mmol) were added
sequentially under an Ar atmosphere. The reaction flask

R. Pathak et al. / Tetrahedron 62 (2006) 2820–2830
2829
(c) Boronic acid 31 (260 mg, 1.59 mmol) was dissolved in
DMF (2 mL) and O2 removed from the solution by three
freeze-thaw cycles. 3-Bromo-5-methoxy-1,2-dimethyl-1H-
indole 30b (200 mg, 0.79 mmol), K3PO4 (0.50 g, 2.4 mmol)
and Pd(PPh3)4 (20 mol%, 0.18 g, 0.16 mmol) were added
sequentially under an Ar atmosphere. The reaction flask was
sealed tightly and heated at 100 8C, for 65 h. After this time
the reaction mixture was cooled and followed by the
addition of saturated solution of brine (15 mL). The reaction
mixture was extracted with Et2O (4!20 mL), the organic
extracts were combined and concentrated under reduced
pressure. Purification of the residue by column chromato-
graphy (20% EtOAc–hexane) afforded the biaryl compound
20b as a yellow-brown oil (0.19 g, 80%); IR nmax/cmK1
1684 (C]O), 1597 and 1617 (C]C), 1489 and 1456; dH
(300 MHz; CDCl3; MeSi4) 1.89 (3H, s, 2-CH3), 2.24 (3H,
s, CH3CO), 3.71 (3H, s, NCH3)a, 3.78 (3H, s, OCH3)a,
6.85–6.88 (2H, m, 2!Ar-H), 7.20 (1H, d, JZ9.5 Hz,
Ar-H), 7.25–7.48 (2H, m, 2!Ar-H) and 7.52–7.57 (1H, m,
Ar-H), 7.62–7.65 (1H, m, Ar-H); dC (75 MHz; CDCl3) 10.9
(2-CH3), 29.7 (CH3CO), 29.8 (NCH3), 55.8 (OCH3), 100.4
(Ar-CH), 109.5 (Ar-CH), 111.4 (Ar-CH), 112.6 (Ar-C),
126.6 (Ar-CH), 127.6 (Ar-C), 128.0 (Ar-CH), 130.8
(Ar-CH), 131.9 (Ar-CH), 133.8 (Ar-C), 135.0 (Ar-C),
142.1 (Ar-C), 154.6 (Ar-C) and 205.1 (CH3CO), (one
quaternary not observed, assignments with same superscript
may be interchanged); MS m/z 294 (MCC1, 21%), 293
(MC, 100), 279 (7), 278 (35), 263 (8), 250 (6), 247 (5), 234
(5), 207 (6), 206 (8) and 165 (5); HRMS calcd for
C19H19NO2: 293.1416, found: MC293.1407.
(0.21 g, 1.9 mmol). The resulting reaction mixture was
stirred at 80 8C and irradiated with a high pressure mercury
lamp through a quartz filter for 10 min. The reaction
was quenched with H2O (15 mL), extracted with Et2O
(3!20 mL) and the organic fractions were combined. The
organic fractions were dried with MgSO4, concentrated
under reduced pressure and the residue purified by column
chromatography (20% EtOAc–hexane) to afford 18b as
yellow crystals (92 mg, 70%). Mp 120 8C; IR nmax/cmK1
1671, 1608 (ArC]C), 1566, 1532 and 1428; dH (400 MHz;
CDCl3; MeSi4) 2.84 (3H, s, ArCH3), 3.88 (3H, s, NCH3)a,
4.01 (3H, s, OCH3)a, 7.11 (1H, dd, JZ8.8, 2.2 Hz, 9-H),
7.37–7.51 (3H, m, 3!Ar-H), 7.68–7.72 (1H, m, Ar-H), 8.00
(1H, d, JZ2.2 Hz, 11-H), 8.12 (1H, d, JZ8.3 Hz, Ar-H)
and 8.71 (1H, d, JZ8.2 Hz, Ar-H); dC (100 MHz; CDCl3)
20.7 (ArCH3), 28.9 (NCH3), 56.3 (OCH3), 105.1 (Ar-CH),
109.4 (Ar-CH), 111.4 (Ar-CH), 112.5 (Ar-CH), 113.1
(Ar-C), 122.4 (Ar-CH), 123.3 (Ar-CH), 123.7 (Ar-C),
125.3 (Ar-CH), 126.5 (Ar-CH), 128.1 (Ar-C), 130.2
(Ar-C), 133.4 (Ar-C), 134.9 (Ar-C), 138.8 (Ar-C) and
154.1 (10-C), (assignments with same superscript may be
interchanged); MS m/z (MCC1, 24%) 275 (MC, 100), 261
(10), 260 (39), 233 (6), 232 (30), 217 (9), 216 (6), 137 (12),
116 (8) and 115 (7); HRMS calcd for C19H17NO: 275.1310,
found: MC275.1308.
Acknowledgements
This work was supported by the National Research
Foundation (NRF, GUN 2053652), Pretoria, the University
of the Witwatersrand (University Research Council and
Faculty Research Council) and the Mellon Postgraduate
Mentoring Programme (sponsored by the Andrew W.
Mellon Foundation). J.M.N. thanks DAAD for a Scholar-
ship and the Mellon Postgraduate Mentoring Programme for
financial assistance. S.G. thanks the NRF for a scarce skills
bursary. Ms. S. Heiss and R. Mampa of this University are
thanked for providing the NMR service.
3.3.19. 5,7-Dimethyl-7H-benzo[c]carbazole 18a. 1-[2-
(1,2-Dimethyl-1H-indol-3-yl)phenyl]ethanone 20a (96 mg,
0.36 mmol) was dissolved in DMF (4 mL) at 80 8C. To the
resulting solution was added tBuOK (0.164 mg,
1.46 mmol). The resulting reaction mixture was stirred at
80 8C and irradiated with a high pressure mercury lamp
through a quartz filter for 10 min. After this time, the
reaction was quenched with H2O (15 mL), extracted with
Et2O (3!20 mL) before the organic fractions were
combined. The fractions were dried with MgSO4, concen-
trated under reduced pressure and the residue purified by
column chromatography (20% EtOAc–hexane) to afford
References and notes
18a as yellow crystals (63 mg, 71%). Mp 112 8C; IR nmax
/
cmK1 1617 and 1591 (ArC]C), 1523, 1465, 1416, 1378; dH
(400 MHz; CDCl3; MeSi4) 2.79 (3H, d, JZ0.9 Hz, ArCH3),
3.79 (3H, s, NCH3), 7.31–7.38 (2H, m, 2!Ar-H), 7.41–7.48
(3H, m, 3!Ar-H), 7.65–7.69 (1H, m, Ar-H), 8.08 (1H, d,
JZ8.4 Hz, Ar-H), 8.50 (1H, d, JZ8.0 Hz, Ar-H) and 8.77
(1H, d, JZ8.2 Hz, Ar-H); dC (100 MHz; CDCl3) 20.6
(ArCH3), 29.0 (NCH3), 108.9 (Ar-CH), 111.2 (Ar-CH),
113.4 (Ar-C), 119.6 (Ar-CH), 121.6 (Ar-CH), 122.5
(Ar-CH), 123.5 (Ar-CH), 123.6 (Ar-CH), 125.2 (Ar-CH),
125.5 (Ar-CH), 126.5 (Ar-CH), 128.2 (Ar-C), 130.2 (Ar-C),
133.4 (Ar-C), 138.2 (Ar-C) and 139.6 (Ar-C); MS m/z
(MCC1, 21%) 245 (MC, 100), 244 (26), 230 (7), 229 (6),
228 (5), 202 (5) and 122 (9); HRMS calcd for C18H15N:
245.1205, found: MC245.1198.23
¨
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´
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2830
R. Pathak et al. / Tetrahedron 62 (2006) 2820–2830
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23. X-ray crystal structures of both 18a and 12 have been achieved
and will be reported in due course.