A versatile and convenient method for the synthesis of substituted benzo[a]carbazoles and pyrido[2,3-a]carbazoles

Article abstract of DOI:10.1039/b001685n

Treatment of 2-(o-tolyl)- or 2-(3-methyl-2-pyridyl)-substituted indole-3-carbaldehydes with potassium tert-butoxide in DMF at 70-80°C with simultaneous irradiation from a 400 W high-pressure mercury lamp afforded benzo[a]carbazoles and pyrido[2,3-a]carbaz

Full text of DOI:10.1039/b001685n

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A versatile and convenient method for the synthesis of substituted
benzo[a]carbazoles and pyrido[2,3-a]carbazoles
Charles B. de Koning,* Joseph P. Michael and Amanda L. Rousseau
1
Centre for Molecular Design, Department of Chemistry, University of the Witwatersrand,
PO Wits, 2050, South Africa
Received (in Cambridge, UK) 1st March 2000, Accepted 10th April 2000
Published on the Web 12th May 2000
Treatment of 2-(o-tolyl)- or 2-(3-methyl-2-pyridyl)-substituted indole-3-carbaldehydes with potassium
tert-butoxide in DMF at 70–80 ЊC with simultaneous irradiation from a 400 W high-pressure mercury
lamp afforded benzo[a]carbazoles and pyrido[2,3-a]carbazoles respectively in good yields.
Introduction
The indole nucleus is often found embedded in compounds
exhibiting a wide range of biological activities.1 Important
members of this class include the benzo- and pyrido-fused
carbazoles,2,3 either as naturally occurring products or as
compounds derived by synthesis. For example, the pyrido-
fused compounds elliptinium (2-methyl-9-hydroxyellipticinium
synthesis of 11H-benzo[a]carbazoles10 and 11H-pyrido[2,3-a]-
carbazoles,10c,11 but none in which the last step involves the
formation of the C-5–C-6 bond.
acetate) 12 and ditercalinium 22 have been used clinically for
Results and discussion
Synthesis of benzo[a]carbazoles
Exposure of oxindole (indolin-2-one) to a mixture of DMF and
phosphorus oxybromide followed by hydrolysis gave 2-bromo-
indole-3-carbaldehyde 7.12 Treatment of 7 with potassium bis-
(trimethylsilyl)amide (KHMDS) and then methyl iodide
afforded the N-methyl precursor 8 in good yield. This precursor
was used in subsequent steps for the synthesis of benzo[a]carb-
azoles. The desired precursors 10a–c were synthesised in high
yields utilising the Suzuki reaction.13 As shown in Scheme 1,
this was achieved by treatment of 8 with the requisite boronic
acid 9a–c in the presence of a catalytic quantity of tetrakis-
the treatment of cancers, while the naphtho[2,3-a]carbazole 3 is
responsible for significant cell growth inhibition of a range
of tumour cell lines.3 A series of simple benzo[a]carbazoles
such as 4 have been shown to bind to estrogen receptors
and inhibit the growth of mammary tumours of rats,4 while
other benzo[a]carbazoles have been suggested as potential anti-
tumour agents.5 Benzo[a]carbazole derivatives have also found
extensive application as photographic materials.6
In this paper we outline novel methodology for the synthesis
of benzo[a]carbazoles and pyrido[2,3-a]carbazoles. This work
is an extension of previous work done towards the synthesis of
naphthalenes and phenanthrenes,7,8 and part of the present
work has been described previously in a communication.9 The
key step involves a novel light-assisted base-induced ring
closure of precursors 5 to form the carbon–carbon bond
between C-5 and C-6 of the benzocarbazole 6 (X = CH)
or pyridocarbazole 6 (X = N) skeleton. It is believed that
this novel cyclisation reaction proceeds through photo-enol
intermediates as described in a previous publication.8 Examin-
ation of the literature reveals a number of methods for the
Scheme 1
DOI: 10.1039/b001685n
J. Chem. Soc., Perkin Trans. 1, 2000, 1705–1713
This journal is © The Royal Society of Chemistry 2000
1705

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Table 1
Indole
Boronic acid 9
Biaryl 10; yield (%)
Benzo[a]carbazole 11; yield (%)
8
8
8
7
a: R2 = R3 = H
a: R1 = Me, R2 = R3 = H; 85
a: R1 = Me, R2 = R3 = H; 77
b: R2 = Me, R3 = H
c: R2 = H, R3 = OMe
a: R2 = R3 = H
b: R1 = Me, R2 = Me, R3 = H; 93
c: R1 = Me, R2 = H, R3 = OMe; 94
d: R1 = Bn, R2 = R3 = H; 84a
b: R1 = Me, R2 = Me; R3 = H; 78b
c: R1 = Me, R2 = H, R3 = OMe; 52
d: R1 = Bn, R2 = R3 = H; 37
a Isolated after N-benzylation of the product from coupling 7 to 9a. b After 5 min. 11e (R1 = Me, R2 = CHO, R3 = H) could also be isolated as minor
product (9%) after 10 min (see Experimental section).
(triphenylphosphine)palladium(0) in 1,2-dimethoxyethane
(DME) and ethanol together with aqueous sodium carbonate to
afford high yields of the desired products 10a–c (Table 1).
To our knowledge this provides the first example of a Suzuki
coupling reaction between substituted aromatic boronic acids
and indoles possessing a carbonyl function at C-3. In the liter-
ature only three related Suzuki coupling reactions involving
2-substituted-indoles and aromatic boronic acids have been
described.14
We found that it was necessary to protect the indole nitrogen
for the next step of the synthesis. However since an N-methyl
group is not easily removed, we chose to prepare the N-benzyl
analogue 10d as well. Treatment of the unprotected indole 7
Scheme 2
with 9a under the same conditions to those described above
sitated a change of strategy, and we investigated a “reversed”
for the formation of 10a–c followed by protection of the indole
Suzuki synthesis in which the indole precursor was made to
bear the boronic acid substituent.
nitrogen with benzyl bromide afforded a high yield of the
benzyl-protected 2-arylindole 10d (Table 1). This strategy
shows that unprotected indoles can successfully participate in
Suzuki coupling reactions.
The synthesis of indole-2-boronic acid 14a has been
described in the literature,16 and Suzuki coupling of 14a with
3-bromopyridine has also been reported.17 As a result we
Evidence for the formation of 10a–d was obtained from both
believed that this methodology could be used to afford the
the 1H and 13C NMR spectra. The aldehyde signal was evident
desired coupled products 13. As outlined in Scheme 3,
at about δ 9.6 and the aromatic methyl signals were found
treatment of indole or 5-methoxyindole with di-tert-butyl
between δ 2.04–2.37, while the N-methyl signal for 10a–c
dicarbonate in the presence of 4-dimethylaminopyridine
appeared at approximately δ 3.5 in the 1H NMR spectrum. The
(DMAP) gave the desired protected indoles 15a–b in excellent
yields. Exposure of each of these compounds to lithium 2,2,6,6-
tetramethylpiperidide (LiTMP) followed by quenching with
triisopropyl borate and hydrolysis with hydrochloric acid
13C NMR spectrum showed the carbon signals of the same
groups at about δ 185, 20 and 30 respectively. The benzyl
1
substituent of 10d was observed in the H NMR spectrum as
a doublet at δ 5.12 with the remaining aromatic protons
provided the desired boronic acids 14a–b. These intermediates
appearing between δ 7.18–7.42.
were not characterised, but used without further purification in
The stage was now set to attempt our novel light-assisted
base-induced cyclisation reaction on indole precursors
the next reaction.
The next step entailed the cross-coupling of the indole-
(Scheme 1). Treatment of the 2-arylindole-3-carbaldehydes
2-boronic acids 14a–b with a suitably substituted pyridine
10a–d with 4 mole equivalents of potassium tert-butoxide
partner. In a similar manner to that described by Johnson
in DMF with simultaneous irradiation from a 400 W high-
et al.,17 treatment of 14a and 14b with 2-bromo-3-
pressure mercury lamp for 10 min afforded the desired carb-
methylpyridine 16 in the presence of a catalytic quantity of
azoles 11a–d in generally good yields (shown in Table 1). For
tetrakis(triphenylphosphine)palladium(0) in 1,2-dimethoxy-
the conversion of 10b→11b over-oxidation afforded aldehyde
11e as a side-product (11e, 9%, 11b, 55%). However on stopping
this reaction after 5 min, only 11b was formed in 78% yield.
Unfortunately, the N-benzyl protected precursor 10d afforded
ethane (DME) together with aqueous sodium carbonate
afforded high yields of the desired products 17a–b. It was clear
from 1H NMR spectroscopy that 17a and 17b had been formed
as diagnostic singlets at about δ 2.2 assigned to the methyl on
11d in mediocre yield. Again, spectroscopic analysis confirmed
the pyridine ring were present in addition to the expected
1
the identity of the products. It was clear from both the H
aromatic signals.
The position of coupling was confirmed by NOE spec-
troscopy of the coupled product 17b. Irradiation of H-3 on the
NMR spectra and the 13C NMR spectra that the aldehyde and
aromatic methyl signals were no longer evident. A characteristic
feature of the carbazole products was a substantial downfield
indole nucleus of 17b showed enhancement of H-4, thus con-
shift of the N-methyl signal (e.g. 10c→11c; δ 3.51→δ 4.12).
firming arylation at C-2. Formation of the carbon–carbon
bond between C-2 of the indole nucleus and a pyridine subunit
has previously proved to be problematic for the synthesis of
Synthesis of pyrido[2,3-a]carbazoles
We envisaged extending the synthesis of benzo[a]carbazoles to
pyrido[2,3-a]carbazoles such as 6 (X = N) in order to gain
access to “angular” analogues of elliptinium and related com-
pounds. We wished to do this as it has been demonstrated that
angular compounds of this type show significant biological
activity.15 However, we found that Suzuki coupling of 8 with
pyridine-2-boronic acids, esters and related compounds 12,
in an analogous manner to that described for preparing
benzo[a]carbazole precursors 10, failed to yield the coupled
products 13 despite numerous attempts (Scheme 2). This neces-
carbazoles as well as carbolines.18 Therefore this method pro-
vides an excellent alternative for the construction of this bond.
As the formation of the 2-(2-pyridyl)indoles 17 had been
completed, an aldehyde functional group had to be introduced
at C-3 of the indole nucleus (Scheme 3). The Boc protecting
group had to be removed to facilitate this reaction. This was
accomplished in high yield (Table 2) by heating 17a and 17b
adsorbed onto silica gel in a conventional microwave oven for
3 min to give 18a and 18b.19 Both of these compounds were
treated under conditions used for the Vilsmeier–Haack
1706
J. Chem. Soc., Perkin Trans. 1, 2000, 1705–1713

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Table 2
17; yield (%)
18; yield (%)
19; yield (%)
13; yield (%)
20; yield (%)
a: R1 = H; 87
a: R1 = H; 100
a: R1 = H; 91
a: R1 = H, R2 = Me; 93
b: R1 = OMe, R2 = Me; 84
c: R1 = H, R2 = Bn; 77
a: R1 = H, R2 = Me; 78
b: R1 = OMe, R2 = Me; 77
c: R1 = H, R2 = Bn; 75
b: R1 = OMe; 77
b: R1 = OMe; 100
b: R1 = OMe; 90
Scheme 4 Reagents and conditions: (i) AlCl3, 0 ЊC, benzene, 80%.
In summary, a new method for the preparation of benzo-
[a]carbazoles and pyrido[2,3-a]carbazoles is described. The
synthesis of benzo[a]carbazoles proceeds in good yield in only
three steps from oxindole (49% for 11a, 54% for 11b, 37% for
11c and 23% for 11d). The synthesis of 20a–c also proceeds in
good overall yield (57% for 20a, 45% for 20b, 46% for 20c)
in only six steps from indole or 5-methoxyindole. Work is in
progress towards the synthesis of pyrido[2,3-c]carbazoles and
these results will be reported in due course.
Experimental
1H NMR and 13C NMR spectra were recorded either on a
Bruker AC-200 or Bruker DRX 400 spectrometer at the
frequency indicated. DEPT, CH-correlated and HMBC spectra
were run on some samples to enable complete assignments of
all the signals. NMR spectroscopic assignments with the same
superscript may be interchanged. 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. Elemental analyses were performed on a Perkin-
Elmer 2400 CHN Elemental Analyser. Macherey-Nagel
Kieselgel 60 (particle size 0.063–0.200 mm) was used for con-
ventional silica gel chromatography and Macherey-Nagel
Kieselgel 60 (particle size 0.040–0.063 mm) was used for pre-
parative flash chromatography. All solvents used for reactions
and chromatography were distilled prior to use.
Scheme 3 Reagents and conditions: (i) LiTMP, Ϫ78 ЊC, THF, (ii)
B(OPri)3, (iii) Hϩ, 14a and 14b, 100% crude (over 3 steps); (iv) 10%
Pd(PPh3)4, aq. Na2CO3, DME; (v) SiO2, microwave oven, 3 min; (vi)
POCl3, DMF; (vii) KHMDS, MeI, THF, for 13a and 13b (viii) BnBr,
KHMDS, THF, for 13c; (ix) KOBut, DMF, hν, 70–80 ЊC (For yields see
Table 2).
2-Bromo-1-methyl-1H-indole-3-carbaldehyde 822
formylation reaction20 to afford the desired products 19a and
19b. It was clear from H NMR spectroscopy that aldehydes
DMF (1.0 cm3, 13.23 mmol) was added to phosphorus oxy-
bromide (3.16 g, 11.02 mmol) at 0 ЊC under an atmosphere of
nitrogen. Oxindole (596 mg, 4.41 mmol) in chloroform (15 cm3)
was added to the resulting salt and the reaction mixture was
stirred at room temperature for 18 h. After this time the reac-
tion was quenched with a saturated aqueous sodium chloride
solution (30 cm3) and made basic with 2 M aqueous sodium
hydroxide. The mixture was extracted with dichloromethane
(3 × 50 cm3) and ethyl acetate (3 × 50 cm3) and the combined
organic fractions were dried (MgSO4) and concentrated under
reduced pressure. The crude 2-bromo-1H-indole-3-carbalde-
hyde 7 was dissolved in THF (20 cm3) and cooled to Ϫ78 ЊC.
Potassium hexamethyldisilazide (KHMDS, 0.5 M solution in
toluene, 10.4 cm3, 5.22 mmol) was added dropwise and the reac-
tion mixture stirred at Ϫ78 ЊC for 45 min. Methyl iodide (0.5
cm3, 8.69 mmol) was added and the reaction mixture stirred
for a further 45 min at Ϫ78 ЊC. After this time the mixture was
warmed to room temperature and stirred for 30 min. The mix-
ture was then quenched with water (50 cm3) and extracted with
diethyl ether (3 × 50 cm3). The organic fractions were combined
and dried (MgSO4) and the solvent removed under reduced
pressure. The crude residue was purified by chromatography
(50% ethyl acetate–hexane) to afford the product 8 (791 mg,
1
19a and 19b had been formed, as singlets were present at δ 9.83
and δ 9.81 respectively. 13C NMR spectroscopy showed inter
alia peaks at δ 185.5 and 185.8. Finally, the indole nitrogen was
protected. Indole 19a was converted into both the methyl-
protected compound 13a as well as the benzyl protected
compound 13c, while indole 19b was converted only into the
methyl-protected compound 13b as shown in Scheme 3.
We were now able to attempt our novel cyclisation reaction
on these precursors. Treatment of 13a–c in DMF with 4 mole
equivalents of potassium tert-butoxide and simultaneous
irradiation from a 400 W high-pressure mercury lamp provided
the desired pyrido[2,3-a]carbazoles 20a–c in good yields. Evi-
dence for the formation of the desired products was obtained
from the NMR spectra. For example, the 1H NMR spectrum of
20c showed that both the aldehyde and methyl signal of the
starting material had been replaced by two doublets at δ 7.40
and δ 8.07 (J = 8.4 Hz) assigned to H-6 and H-5 respectively.
The benzyl-protected compound 19c was treated with
aluminium trichloride in benzene21 to afford 21 (Scheme 4),
illustrating the value of a selectively removable protecting
group.
J. Chem. Soc., Perkin Trans. 1, 2000, 1705–1713
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75% over two steps) isolated as a white solid; mp 111–112 ЊC
(ethanol) (lit.,22a 110–111.5 ЊC) (Found: Mϩ 236.9799.
C10H8ONBr requires M, 236.9789); νmax(CHCl3)/cmϪ1 3015
aldehyde 8 and 4-methoxy-2-methylphenylboronic acid 9c;
mp 203–206 ЊC (toluene) (Found: Mϩ 279.1248. C18H17NO2
requires M, 279.1259); νmax(CHCl3)/cmϪ1 3017 (ArC–H), 2839
(ArC–H), 1653 (C᎐O) and 1501 (ArC᎐C); δ (200 MHz;
(OCH ), 1647 (C᎐O), 1610, 1580 and 1539 (ArC᎐C), 1243
᎐ ᎐
3
᎐
᎐
H
CDCl3; Me4Si) 3.76 (3H, s, NCH3), 7.29–7.32 (3H, m,
3 × ArH), 8.28–8.32 (1H, m, 7-H) and 10.01 (1H, s, CHO); δC
(50.32 MHz; CDCl3) 31.4 (NCH3), 109.5 (7-C), 114.8 (3-C),
120.6 (6-C)a, 123.0 (5-C)a, 123.8 (4-C)a, 124.7 (2-C)b, 126.3 (4a-
C)b, 137.0 (7a-C)b and 185.0 (CHO); m/z 236 (Mϩ, 82%), 235
(100), 157 (7), 129 (30), 89 (22) and 63 (18).
(C–O) and 820 (ArH oop); δH (400 MHz; CDCl3; Me4Si) 2.12
(3H, s, ArCH3), 3.51 (3H, s, NCH3), 3.87 (3H, s, OCH3), 6.86
(1H, dd, J 2.4 and 8.4, 5Ј-H), 6.91 (1H, d, J 2.4, 3Ј-H), 7.22 (1H,
d, J 8.4, 6Ј-H), 7.34–7.39 (3H, m, 3 × ArH), 8.38–8.43 (1H, m,
7-H) and 9.58 (1H, s, CHO); δC (100.625 MHz; CDCl3) 20.1
(ArCH3), 30.2 (NCH3), 55.3 (OCH3), 109.6 (7-C), 111.3 (3Ј-C)a,
115.8 (5Ј-C)a, 115.9 (3-C), 120.3 (3a-C)b, 121.9 (6Ј-C)a, 123.0
(6-C)c, 123.6 (5-C)c, 125.1 (2-C)b, 132.3 (4-C)c, 137.2 (2Ј-C)d,
139.8 (1Ј-C)d, 151.5 (7a-C), 160.8 (4Ј-C) and 186.2 (CHO);
m/z 279 (Mϩ, 83%), 278 (21), 264 (41), 262 (100), 250 (12) and
249 (15).
General procedure for the coupling of arylboronic acids to indoles
Typically, a solution of 2-bromo-1-methyl-1H-indole-3-carb-
aldehyde 8 or 2-bromo-1H-indole-3-carbaldehyde 7 (0.78
mmol) in DME (4 cm3) was deoxygenated by passing nitrogen
through the mixture for 5 min. The deoxygenated mixture was
added to Pd(PPh3)4 (10%, 0.08 mmol) and stirred under an
atmosphere of nitrogen at room temperature for 10 min. A
solution of 2-methylphenylboronic acid 9a,23 2,3-dimethyl-
phenylboronic acid 9b24 or 4-methoxy-2-methylphenylboronic
acid 9c25 (1.16 mmol) in ethanol (1.5 cm3) was deoxygenated
and added to the mixture. The mixture was stirred for a further
10 min. A 2 M aqueous sodium carbonate solution (6.60 mmol)
was also deoxygenated and added to the reaction mixture. The
mixture was stirred for 5 min at room temperature before being
heated at reflux for 18 h. The mixture was cooled to room tem-
perature and quenched with water (20 cm3). The organic
material was extracted into dichloromethane (3 × 30 cm3), the
combined organic extracts were dried with magnesium sulfate
and the solvent was evaporated under reduced pressure. The
crude product was subjected to chromatography (10–30% ethyl
acetate–hexane). The following compounds were prepared by
this method.
1-Benzyl-2-(2-methylphenyl)-1H-indole-3-carbaldehyde 10d.
2-Bromo-1H-indole-3-carbaldehyde 7 (431 mg, 1.93 mmol) was
treated with 2-methylphenylboronic acid 9a as described in the
general procedure to afford 2-(2-methylphenyl)-1H-indole-3-
carbaldehyde (428 mg, 95%) as an off-white solid. This product
was treated as an intermediate. A portion of the product (136
mg, 0.58 mmol) was dissolved in THF (5 cm3) and cooled to
Ϫ78 ЊC. Potassium hexamethyldisilazide (KHMDS, 0.5 M
solution in toluene, 1.7 cm3, 0.87 mmol) was added dropwise
and the reaction mixture stirred at Ϫ78 ЊC for 30 min. Benzyl
bromide (0.2 cm3, 1.45 mmol) was added and the reaction mix-
ture stirred for a further 30 min at Ϫ78 ЊC. After this time the
mixture was warmed to room temperature and stirred for 30
min. The mixture was then quenched with water (50 cm3) and
extracted with ethyl acetate (3 × 50 cm3). The organic fractions
were combined and dried (MgSO4) and the solvent removed
under reduced pressure. The crude residue was purified by
chromatography (5–20% ethyl acetate–hexane) to afford the
product 10d (159 mg, 84%) as a clear oil (Found: Mϩ 325.1472.
C23H19NO requires M, 325.1467); νmax(film)/cmϪ1 3032 (ArC–
1-Methyl-2-(2-methylphenyl)-1H-indole-3-carbaldehyde 10a.
The product 10a (164 mg, 85%) was isolated as an off-white
solid from 2-bromo-1-methyl-1H-indole-3-carbaldehyde 8 and
2-methylphenylboronic acid 9a; mp 165–166.5 ЊC (ethyl
acetate–methanol) (Found: Mϩ 249.1146. C17H15NO requires
H), 1653 (C᎐O), 1611, 1580 and 1538 (ArC᎐C), 1454 (C–N) and
᎐
᎐
750 (ArH oop); δH (200 MHz; CDCl3; Me4Si) 2.04 (3H, s,
ArCH3), 5.12 (2H, d, J 7.6, NCH2Ph), 6.86–6.90 (2H, m,
2 × ArH), 7.18–7.42 (10H, m, 10 × ArH), 8.41–8.45 (1H, m,
ArH) and 9.60 (1H, s, CHO); δC (50.32 MHz; CDCl3) 19.9
(ArCH3), 47.5 (NCH2Ph), 110.7 (7-C), 116.1 (3-C), 122.2
(4-C)a, 123.2 (6-C)a, 123.9 (5-C)a, 125.3 (2-C), 125.8 (ArCH)a,
126.5 (2 × ArCH), 127.7 (5Ј-C)a, 128.2 (ArC), 128.7
(2 × ArCH), 130.2 (6Ј-C)b, 130.4 (4Ј-C)b, 131.0 (3Ј-C)b, 135.9
(3a-C)c, 136.8 (2Ј-C)c, 138.4 (1Ј-C)c, 151.2 (7a-C) and 186.3
(CHO); m/z 325 (Mϩ, 56%), 324 (9), 310 (15), 308 (27), 204 (11)
and 91 (100).
M, 249.1154); νmax(CHCl3)/cmϪ1 3016 (ArC–H), 1647 (C᎐O),
᎐
1614, 1571 and 1528 (ArC᎐C) and 818 (ArH oop); δ (200
᎐
H
MHz; CDCl3; Me4Si) 2.15 (3H, s, ArCH3), 3.52 (3H, s, NCH3),
7.31–7.46 (7H, m, 7 × ArH), 8.40–8.44 (1H, m, 7-H) and 9.57
(1H, s, CHO); δC (50.32 MHz; CDCl3) 19.8 (ArCH3), 30.3
(NCH3), 109.7 (7-C), 115.7 (3-C), 122.0 (3Ј-C)a, 123.2 (4Ј-C)a,
123.8 (5Ј-C)a, 125.1 (3a-C)b, 125.8 (6Ј-C)a, 128.4 (2-C)b, 130.1
(5-C)c, 131.1 (4-C)c, 137.3 (2Ј-C)d, 138.2 (1Ј-C)d, 151.3 (7a-C)
and 186.0 (CHO); m/z 249 (Mϩ, 100%), 248 (34), 235 (10), 234
(52) and 232 (96).
General procedure for cyclisation of 2-arylindole-3-carbalde-
hydes to benzo[a]carbazoles
1-Methyl-2-(2,3-dimethylphenyl)-1H-indole-3-carbaldehyde
10b. The product 10b (115 mg, 99%) was isolated as an off-white
solid from 2-bromo-1-methyl-1H-indole-3-carbaldehyde 8 and
2,3-dimethylphenylboronic acid 9b; mp 157–159 ЊC (ethyl
acetate) (Found: Mϩ 263.1327. C18H17NO requires M,
Typically, the 2-aryl-3-acylindole (0.43 mmol) was dissolved
in dry DMF (15 cm3) and heated to 80 ЊC under nitrogen.
Potassium tert-butoxide (1.72 mmol) was added and the reac-
tion mixture was irradiated with a high-pressure mercury lamp
through a quartz filter for 10 min. The reaction mixture was
diluted with water and the organic material was extracted into
diethyl ether. The organic fractions were combined, dried with
magnesium sulfate and filtered. The diethyl ether was then
evaporated under reduced pressure and the resulting residue
was subjected to chromatography (5–20% ethyl acetate–hexane)
to afford the desired benzo[a]carbazoles. The following com-
pounds were prepared by this method.
263.1310); νmax(CHCl3)/cmϪ1 3105 (ArC–H), 1647 (C᎐O), 1613,
᎐
1581 and 1535 (ArC᎐C) and 817 (ArH oop); δ (200 MHz;
᎐
H
CDCl3; Me4Si) 2.04 and 2.37 (each 3H, s, ArCH3), 3.51 (3H, s,
NCH3), 7.15 (1H, dd, J 1.7 and 7.5, 5Ј-H), 7.24 (1H, dd, J 7.5
and 9.2, 4Ј-H), 7.32–7.42 (4H, m, 4 × ArH), 8.39–8.44 (1H, m,
7-H) and 9.57 (1H, s, CHO); δC (100.625 MHz; CDCl3) 16.8
and 20.2 (each ArCH3), 30.3 (NCH3), 109.7 (7-C), 115.8 (3-C),
122.0 (4Ј-C)a, 123.1 (5Ј-C)a, 123.7 (6-C)a, 125.0 (3a-C)b, 125.5
(6Ј-C)a, 128.3 (2-C)b, 128.9 (5-C)c, 131.5 (4-C)c, 136.7 (3Ј-C)d,
137.1 (2Ј-C)d, 137.7 (1Ј-C)d, 152.2 (7a-C) and 186.2 (CHO); m/z
263 (Mϩ, 100%), 262 (19), 249 (15), 248 (82) and 218 (26).
11-Methyl-11H-benzo[a]carbazole 11a. The product 11a (107
mg, 77%) was isolated as a pale yellow solid; mp 171–172.5 ЊC
(ethyl acetate–methanol) (Found: Mϩ 231.1043. C17H13N
requires M, 231.1048); νmax(CHCl3)/cmϪ1 3058 (ArC–H), 1577,
2-(4-Methoxy-2-methylphenyl)-1-methyl-1H-indole-3-carb-
aldehyde 10c. The product 10c (117 mg, 94%) was isolated as
a pale yellow solid from 2-bromo-1-methyl-1H-indole-3-carb-
1560 and 1528 (ArC᎐C) and 809 (ArH oop); δ (400 MHz;
᎐
H
CDCl3; Me4Si) 4.19 (3H, s, NCH3), 7.26 (1H, ddd, J 1.8, 6.0 and
1708
J. Chem. Soc., Perkin Trans. 1, 2000, 1705–1713

View Article Online
6.8, 8-H), 7.39–7.51 (4H, m, 2-H, 3-H, 9-H and 10-H), 7.57
(1H, d, J 8.5, 6-H)a, 7.95 (1H, dd, J 1.8 and 7.6, 4-H), 8.07 (1H,
d, J 8.5, 5-H)a, 8.08 (1H, dd, J 1.3 and 6.8, 7-H) and 8.57 (1H,
dd, J 1.0 and 8.0, 1-H); δC (50.32 MHz; CDCl3) 33.7 (NCH3),
108.9 (10-C), 118.7 (4a-C)a, 119.0 (7-C), 119.4 (8-C), 119.6
(5-C), 120.3 (6-C), 122.0 (1-C), 122.6 (7a-C)a, 122.9 (6a-C)a,
124.5 (3-C)b, 124.6 (9-C)b, 125.0 (2-C)b, 129.3 (4-C), 133.5 (10a-
C)c, 135.3 (1a-C)c and 140.6 (11a-C)c; m/z 231 (Mϩ, 100%), 230
(22), 216 (27), 202 (7) and 116 (9).
M, 307.1361); νmax(CHCl3)/cmϪ1 3020 (ArC–H), 1523 (ArC᎐C),
1424 (C–N) and 787 (ArH oop); δH (400 MHz; CDCl3; Me4Si)
᎐
6.01 (2H, s, NCH2Ph), 7.23–7.41 (7H, m, 7 × ArH), 7.42–7.47
(3H, m, 3 × ArH), 7.69 (1H, d, J 8.5, 6-H)a, 8.00 (1H, ddd,
J 0.6, 1.3 and 8.0, 4-H), 8.20 (1H, dd, J 0.8 and 7.7, 7-H), 8.22
(1H, d, J 8.5, 5-H)a and 8.25 (1H, dd, J 0.6 and 8.6, 1-H); δC
(100.625 MHz; CDCl3) 49.7 (NCH2Ph), 109.3 (10-C), 119.1
(7-C)a, 119.4 (4a-C)b, 119.7 (8-C)a, 120.0 (5-C)a, 120.9 (6-C)a,
122.0 (1-C)a, 122.1 (7a-C)b, 123.3 (6a-C)b, 124.6 (3-C)c, 125.1
(9-C)c, 125.4 (2-C)c, 126.0 (2 × ArCH), 127.5 (ArCH), 129.1
(2 × ArCH), 129.4 (4-C), 133.6 (10a-C)d, 135.3 (1a-C)d, 137.5
(ArC)d and 141.1 (11a-C)d; m/z 307 (Mϩ, 100%), 306 (4), 216
(89) and 91 (78).
4,11-Dimethyl-11H-benzo[a]carbazole 11b and 11-methyl-
11H-benzo[a]carbazole-4-carbaldehyde 11e. 4,11-Dimethyl-
11H-benzo[a]carbazole 11b (139 mg, 78%) was isolated as a
white solid (reaction time 5 min); mp 192–193.5 ЊC (ethyl acet-
ate) (Found: Mϩ 245.1208. C18H15N requires M, 245.1205);
tert-Butyl 1H-indole-1-carboxylate 15a. Indole (2.00 g, 17.11
mmol) was dissolved in THF (150 cm3) and treated with
4-dimethylaminopyridine (21 mg, 0.17 mmol) and di-tert-butyl
dicarbonate (4.11 g, 18.82 mmol). The mixture was stirred at
room temperature under an atmosphere of nitrogen for 16 h.
The solvent was then removed under reduced pressure and the
crude residue was purified by chromatography (10% ethyl
acetate–hexane) to afford the product 15a (3.72 g, 100%) as a
clear oil identical in all respects with that described in the
literature;26 δH (200 MHz; CDCl3; Me4Si) 1.67 [9H, s, CO2C-
(CH3)3], 6.56 (1H, d, J 3.8, 3-H), 7.21–7.25 (1H, m, 5-H), 7.27–
7.31 (1H, m, 6-H) and 7.53–7.58 (1H, m, 4-H); δC (100.625
MHz; CDCl3) 28.2 [CO2C(CH3)3], 83.6 [CO2C(CH3)3], 107.2
(3-C), 115.1 (7-C), 120.9 (5-C)a, 122.6 (6-C)a, 124.1 (4-C)a, 125.8
(2-C)a, 130.5 (3a-C)b, 135.2 (7a-C)b and 149.8 [CO2C(CH3)3].
νmax(CHCl3)/cmϪ1 3019 (ArC–H), 1595 and 1535 (ArC᎐C) and
᎐
913 (ArH oop); δH (200 MHz; CDCl3; Me4Si) 2.77 (3H, s,
ArCH3), 4.29 (3H, s, NCH3), 7.25–7.34 (1H, m, 10-H), 7.37–
7.46 (2H, m, 2-H and 3-H), 7.46–7.49 (2H, m, 8-H and 9-H),
7.77 (1H, dd, J 0.9 and 8.8, 5-H), 8.13 (1H, dd, J 1.4 and 7.8,
7-H), 8.15 (1H, d, J 8.8, 6-H) and 8.53 (1H, d, J 8.3, 1-H);
δC (50.32 MHz; CDCl3) 20.9 (ArCH3), 34.1 (NCH3), 109.0
(10-C), 116.2 (7-C)a, 118.8 (8-C)a, 119.4 (5-C)a, 119.6 (6-C)a,
120.4 (1-C)a, 122.6 (6a-C)b, 122.9 (7a-C)b, 124.6 (3-C)c, 124.7
(9-C)c, 125.8 (2-C)c, 132.4 (4a-C)b, 135.4 (4-C and 10a-C)b,
136.1 (1a-C)d and 140.9 (11a-C)d; m/z 245 (Mϩ, 100%), 244 (16),
230 (23), 202 (5), 150 (8) and 122 (8).
A
second product, 11-methyl-11H-benzo[a]carbazole-4-
carbaldehyde 11e was isolated when the reaction mixture was
irradiated for 10 min, as described in the general procedure.
Chromatography (5% ethyl acetate–hexane) afforded firstly
4,11-dimethyl-11H-benzo[a]carbazole 11b (46 mg, 55%) identi-
cal in all respects with that described above, followed by the
aldehyde 11e (8 mg, 9%) isolated as a yellow solid; mp 155–
157 ЊC (ethanol) (Found: Mϩ 259.0995. C18H13NO requires M,
tert-Butyl 5-methoxy-1H-indole-1-carboxylate 15b. 5-Meth-
oxyindole (1.06 g, 7.10 mmol) was dissolved in THF (70 cm3)
and treated with dimethylaminopyridine (9 mg, 0.07 mmol) and
di-tert-butyldicarbonate (1.70 g, 7.81 mmol). The mixture was
stirred at room temperature under an atmosphere of nitrogen
for 16 h. The solvent was then removed under reduced pressure
and the crude residue was purified by chromatography (5%
ethyl acetate–hexane) to afford the product 15b (1.76 g, 100%)
as a clear oil which crystallised on standing, identical in all
respects with that decribed in the literature;27 mp 74–76 ЊC
(ethyl acetate–hexane) [lit.,27 75–76 ЊC (methanol)]; δH (200
MHz; CDCl3; Me4Si) 1.65 [9H, s, CO2C(CH3)3], 3.83 (3H, s,
OCH3), 6.48 (1H, d, J 3.7, 3-H), 6.92 (1H, dd, J 2.5 and 9.0,
6-H), 7.01 (1H, d, J 2.5, 4-H), 7.55 (1H, d, J 3.7, 2-H) and
8.02 (1H, br d, J 9.0, 7-H); δC (50.32 MHz; CDCl3) 28.1
[CO2C(CH3)3], 55.6 (OCH3), 83.4 [CO2C(CH3)3], 103.4 (3-C)a,
107.0 (6-C)a, 112.9 (4-C)a, 115.8 (7-C)a, 126.4 (2-C), 129.9
(7a-C)b, 131.3 (3a-C)b, 149.5 (5-C) and 155.8 [CO2C(CH3)3].
259.0997); νmax(CHCl3)/cmϪ1 3017 (ArC–H), 1690 (C᎐O), 1653,
᎐
1591 and 1559 (ArC᎐C) and 826 (ArH oop); δ (200 MHz;
᎐
H
CDCl3; Me4Si) 4.41 (3H, s, NCH3), 7.32–7.40 (1H, m, 10-H),
7.51–7.61 (2H, m, 8-H and 9-H), 7.74 (1H, dd, J 7.1 and 8.6,
2-H), 8.05 (1H, dd, J 1.2 and 7.1, 3-H), 8.21 (1H, dd, J 1.0 and
7.8, 7-H), 8.39 (1H, d, J 8.9, 6-H), 9.00 (1H, dd, J 1.2 and 8.6,
1-H), 9.10 (1H, dd, J 0.8 and 8.9, 5-H) and 10.53 (1H, s, CHO);
δC (50.32 MHz; CDCl3) 34.3 (NCH3), 109.1 (10-C), 115.7
(7-C)a, 119.7 (4a-C)b, 119.9 (5-C and 8-C)a, 122.3 (6-C)a, 122.7
(6a-C)b, 123.0 (7a-C)b, 123.8 (9-C)c, 125.4 (3-C)c, 128.7 (2-C)c,
130.5 (4-C)d, 131.6 (10a-C)d, 135.2 (1a-C)e, 140.6 (11a-C)e and
193.6 (CHO); m/z 259 (Mϩ, 100%), 231 (86), 230 (39), 216 (38),
202 (14), 129 (13) and 115 (15).
3-Methoxy-11-methyl-11H-benzo[a]carbazole
11c.
The
General method for the preparation of indoleboronic acids
desired product 11c (103 mg, 52%) was isolated as a pale yellow
oil that crystallised on standing; mp 169–171 ЊC (ethyl acetate)
(Found: Mϩ 261.1156. C18H15NO requires M, 261.1154);
νmax(CHCl3)/cmϪ1 3009 (ArC–H), 2853 (OCH3), 1622 and 1568
Typically, tetramethylpiperidine (5.15 mmol) in THF (10 cm3)
was cooled to Ϫ78 ЊC under an atmosphere of nitrogen and
treated with n-butyllithium (4.3 cm3, 5.85 mmol). The mixture
was stirred at Ϫ78 ЊC for 10 min, then warmed to 0 ЊC within 30
min. The mixture was again cooled to Ϫ78 ЊC and the lithium
tetramethylpiperidide generated was treated with tert-butyl 1H-
indole-1-carboxylate 15a or tert-butyl 5-methoxy-1H-indole-1-
carboxylate 15b (4.68 mmol) in THF (20 cm3). The mixture was
stirred at Ϫ78 ЊC for 80 min. Freshly distilled triisopropyl
borate (7.02 mmol) in THF (10 cm3) was then added, and the
reaction mixture was stirred for 30 min at Ϫ78 ЊC before being
warmed to room temperature. The reaction mixture was
quenched with water (50 cm3), acidified with an aqueous 10%
hydrochloric acid solution, and extracted into ethyl acetate
(3 × 50 cm3). The combined organic phases were dried with
magnesium sulfate and the solvent was evaporated under
reduced pressure to afford off-white crystalline materials in
quantitative yields, which were used without further purifi-
cation or characterisation. 1-(tert-Butoxycarbonyl)-1H-indol-2-
(ArC᎐C), 1208 (C–O) and 855 (ArH oop); δ (200 MHz;
᎐
H
CDCl3; Me4Si) 3.91 (3H, s, OCH3), 4.12 (3H, s, NCH3), 7.16
(1H, dd, J 2.5 and 9.3, 2-H), 7.24–7.28 (1H, m, 10-H), 7.30 (1H,
d, J 2.5, 4-H), 7.40–7.43 (2H, m, 8-H and 9-H), 7.48 (1H, d,
J 8.5, 5-H), 8.06 (1H, d, J 8.5, 6-H), 8.07 (1H, dd, J 1.2 and 7.4,
7-H) and 8.47 (1H, d, J 9.3, 1-H); δC (100.625 MHz; CDCl3)
33.8 (NCH3), 55.3 (OCH3), 108.4 (10-C)a, 108.8 (2-C)a, 116.8
(4-C)a, 117.5 (4a-C)b, 117.6 (7a-C)b, 119.3 (7-C)c, 119.4 (8-C)c,
119.5 (5-C)c, 119.7 (6-C)c, 123.1 (6a-C)b, 123.6 (1-C)d, 124.2
(9-C)d, 135.2 (10a-C)e, 135.9 (1a-C)e, 140.5 (11a-C)e and 156.6
(3-C); m/z 261 (Mϩ, 100%), 246 (4), 218 (45), 130 (13) and 108
(10).
11-Benzyl-11H-benzo[a]carbazole 11d. The product 11d (56
mg, 37%) was isolated as a colourless solid; mp 145–147 ЊC
(ethyl acetate–hexane) (Found: Mϩ 307.1378. C23H17N requires
J. Chem. Soc., Perkin Trans. 1, 2000, 1705–1713
1709

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ylboronic acid 14a and 1-(tert-butoxycarbonyl)-5-methoxy-1H-
indol-2-ylboronic acid 14b were prepared by this method.
containing the mixture was then placed in an alumina bath
and irradiated with microwave radiation from a conventional
700 W microwave oven on 100% power for 3 min. The product
was washed from the silica with ethyl acetate (3 × 30 cm3) and
acetone (3 × 30 cm3) and the solvent was evaporated under
reduced pressure. The resulting residue was subjected to
column chromatography (10% ethyl acetate–hexane) to afford
the product 17a (165 mg, 96%) as a pale yellow solid; mp 162–
163.5 ЊC (methanol) (Found: Mϩ 208.0990. C14H12N2 requires
M, 208.1001); νmax(CHCl3)/cmϪ1 3112 (NH), 3019 (ArC–H),
tert-Butyl 2-(3-methyl-2-pyridyl)-1H-indole-1-carboxylate 17a
A deoxygenated solution of 1-(tert-butoxycarbonyl)-1H-indol-
2-ylboronic acid 14a (489 mg, 1.87 mmol) and 2-bromo-3-
methylpyridine 16 (226 mg, 1.25 mmol) in DME (15 cm3) was
added to Pd(PPh3)4 (10%, 144 mg, 0.12 mmol) under a nitrogen
atmosphere with stirring. To this was added a deoxygenated
aqueous sodium carbonate solution (2 M, 2.6 cm3, 556 mg, 5.2
mmol). The mixture was then heated at reflux for 18 h. After
this time the mixture was cooled to room temperature and
quenched with water (15 cm3). The organic material was
extracted into dichloromethane (3 × 30 cm3) and the combined
organic extracts dried with sodium sulfate. The solvent was
evaporated under reduced pressure and the resulting residue
subjected to column chromatography (10–30% ethyl acetate–
hexane) to afford the product 17a (383 mg, 99%) as a clear oil
(Found: Mϩ 308.1513. C19H20N2O2 requires M, 308.1525);
νmax(film)/cmϪ1 2980 (ArC–H), 1734 (CO2R), 1586 and 1561
1586 and 1522 (ArC᎐C), 1419 (C–N) and 794 (ArH oop); δ
᎐
H
(400 MHz; CDCl3 and DMSO-d6; Me4Si) 2.64 (3H, s, ArCH3),
6.97 (1H, s, 3-H), 7.08 (1H, dd, J 4.6 and 7.7, 5Ј-H), 7.10–7.12
(1H, m, 6-H), 7.20–7.24 (1H, m, 5-H), 7.39 (1H, dd, J 0.8 and
8.2, 4-H), 7.53 (1H, dd, J 0.9 and 7.7, 4Ј-H), 7.67 (1H, dd, J 0.7
and 7.9, 7-H), 8.47 (1H, dd, J 0.9 and 4.6, 6Ј-H) and 10.00
(1H, br s, NH); δC (50.32 MHz; CDCl3 and DMSO-d6) 21.5
(ArCH3), 104.3 (3-C), 111.1 (7-C)a, 119.8 (5-C)a, 121.3 (6-C)a,
121.6 (2-C), 123.3 (4-C)a, 129.4 (5Ј-C)a, 130.7 (3Ј-C)a, 135.5
(4Ј-C), 136.1 (3a-C), 139.3 (6Ј-C), 146.4 (7a-C) and 148.7
(2Ј-C); m/z 208 (Mϩ, 99%), 207 (100), 180 (9) and 103 (13).
(ArC᎐C) and 1337 (C–O); δ (400 MHz; CDCl3; Me4Si) 1.25
᎐
H
[9H, s, CO2C(CH3)3], 2.24 (3H, s, ArCH3), 6.61 (1H, s, 3-H),
7.19 (1H, dd, J 4.8 and 7.7, 5Ј-H), 7.22–7.25 (1H, m, 5-H), 7.34
(1H, ddd, J 1.1, 7.3 and 8.4, 6-H), 7.52 (1H, dd, J 0.8 and 7.7,
4Ј-H), 7.56 (1H, d, J 7.7, 4-H), 8.27 (1H, d, J 8.4, 7-H) and 8.48
(1H, dd, J 0.8 and 4.8, 6Ј-H); δC (100.625 MHz; CDCl3) 18.9
(ArCH3), 27.4 [CO2C(CH3)3], 82.9 [CO2C(CH3)3], 109.9 (3-C),
115.3 (5Ј-C)a, 120.6 (5-C)a, 122.6 (6-C)a, 122.7 (4Ј-C)a, 124.4
(4-C)a, 129.0 (2-C)b, 132.6 (3a-C)b, 136.6 (7a-C)b, 137.2 (7-C),
137.6 (3Ј-C), 146.1 (6Ј-C), 149.6 (2Ј-C) and 153.2 [CO2C-
(CH3)3]; m/z 308 (Mϩ, 17%), 235 (6), 208 (100), 207 (64) and
57 (46).
5-Methoxy-2-(3-methyl-2-pyridyl)-1H-indole 18b
tert-Butyl 5-methoxy-2-(3-methyl-2-pyridyl)-1H-indole-1-carb-
oxylate 17b (176 mg, 0.52 mmol) was dissolved in dichloro-
methane (30 cm3) and adsorbed onto silica gel 60 (70–230 mesh,
5 g). The flask containing the mixture was then placed in an
alumina bath and irradiated with microwave radiation from a
conventional 700 W microwave oven on 100% power for 3 min.
The product was washed from the silica with ethyl acetate
(3 × 30 cm3) and acetone (3 × 30 cm3) and the solvent was
evaporated under reduced pressure. The resulting residue was
subjected to column chromatography (10–20% ethyl acetate–
hexane) to afford the product 18b (106 mg, 86%) as an off-white
solid; mp 122–123 ЊC (methanol) (Found: Mϩ 238.1115. C15H14-
N2O requires M, 238.1106); νmax(CHCl3)/cmϪ1 3446 (NH), 3008
tert-Butyl 5-methoxy-2-(3-methyl-2-pyridyl)-1H-indole-1-carb-
oxylate 17b
A
deoxygenated solution of 1-(tert-butoxycarbonyl)-5-
(ArC–H), 1585, 1572 and 1535 (ArC᎐C), 1441 (C–N), 1208
᎐
methoxy-1H-indol-2-ylboronic acid 14b (303 mg, 1.04 mmol)
and 2-bromo-3-methylpyridine 16 (126 mg, 0.69 mmol) in
DME (5 cm3) was added to Pd(PPh3)4 (10%, 80 mg, 0.07 mmol)
under a nitrogen atmosphere with stirring. To this was added
a deoxygenated aqueous sodium carbonate solution (2 M,
1.5 cm3, 309 mg, 2.9 mmol). The mixture was then heated at
reflux for 18 h. After this time the mixture was cooled to room
temperature and quenched with water (10 cm3). The organic
material was extracted into ethyl acetate (3 × 30 cm3) and the
combined organic extracts dried with magnesium sulfate. The
solvent was evaporated under reduced pressure and the crude
residue purified by column chromatography (10–20% ethyl
acetate–hexane) to afford the product 17b (182 mg, 77%) as
a clear oil (Found: Mϩ 338.1640. C20H22N2O3 requires M,
338.1630); νmax(film)/cmϪ1 2980 (ArC–H), 2848 (OCH3), 1729
(OCH3) and 839 (ArH oop); δH (200 MHz; CDCl3 and DMSO-
d6; Me4Si) 2.63 (3H, s, ArCH3), 3.86 (3H, s, OCH3), 6.89 (1H,
dd, J 2.5 and 8.8, 6-H), 6.91 (1H, dd, J 0.7 and 2.5, 4-H), 7.08
(1H, dd, J 4.7 and 7.7, 5Ј-H), 7.12 (1H, s, 3-H), 7.28 (1H, dd,
J 0.7 and 8.8, 7-H), 7.53 (1H, dd, J 1.7 and 7.7, 4Ј-H), 7.46 (1H,
dd, J 1.7 and 4.7, 6Ј-H) and 9.94 (1H, br s, NH); δC (100.625
MHz; CDCl3) 21.4 (ArCH3), 55.8 (OCH3), 102.4 (3-C)a, 103.8
(4-C)a, 111.9 (6-C)a, 113.9 (5Ј-C)a, 121.4 (7-C)a, 129.6 (2-C)b,
130.5 (3a-C)b, 130.9 (7a-C)b, 136.7 (3Ј-C)b, 139.3 (4Ј-C), 146.3
(6Ј-C), 148.7 (2Ј-C)c and 154.1 (5-C)c; m/z 238 (Mϩ, 100%), 223
(63), 195 (31), 168 (6), 119 (7) and 97 (5).
2-(3-Methyl-2-pyridyl)-1H-indole-3-carbaldehyde 19a
Phosphorus oxychloride (0.08 cm3, 0.87 mmol) was added
dropwise to dry DMF (0.27 cm3, 3.49 mmol) at 0 ЊC. The result-
ing mixture was warmed to room temperature and treated with
2-(3-methyl-2-pyridyl)-1H-indole 18a (165 mg, 0.79 mmol) in
DMF (3 cm3). The mixture was heated to 35 ЊC and left stirring
at this temperature under a nitrogen atmosphere for 1 h. After
this time, ice was added and the mixture was made basic with
2 M aqueous sodium hydroxide. The mixture was then heated
at reflux for 30 min. Once the mixture had cooled, the organic
material was extracted into chloroform (3 × 30 cm3) and the
combined organic extracts were dried (MgSO4) and concen-
trated under reduced pressure. The resulting residue was sub-
jected to column chromatography (20% ethyl acetate–hexane
followed by 10% methanol–ethyl acetate) to afford the product
19a (171 mg, 91%) as an off-white solid; mp 203–204.5 ЊC
(methanol) (Found: Mϩ 236.0960. C15H12N2O requires M,
236.0950); νmax(CHCl3)/cmϪ1 3450 (NH), 3019 (ArC–H), 1656
(CO R), 1625 and 1586 (ArC᎐C), 1235 (C–O) and 850 (ArH
᎐
2
oop); δH (200 MHz; CDCl3; Me4Si) 1.25 [9H, s, CO2C(CH3)3],
2.24 (3H, s, ArCH3), 3.86 (3H, s, OCH3), 6.54 (1H, s, 3-H), 6.96
(1H, dd, J 2.4 and 9.0, 6-H), 7.04 (1H, d, J 2.4, 4-H), 7.21 (1H,
dd, J 4.8 and 7.7, 5Ј-H), 7.55 (1H, dd, J 0.6 and 7.7, 4Ј-H), 8.15
(1H, dd, J 0.6 and 9.0, 7-H) and 8.49 (1H, dd, J 0.6 and
4.8, 6Ј-H); δC (50.32 MHz; CDCl3) 18.9 (ArCH3), 27.5
[CO2C(CH3)3], 55.6 (OCH3), 82.9 [CO2C(CH3)3], 103.1 (3-C),
109.8 (6-C), 113.3 (4-C), 116.2 (5Ј-C), 122.7 (4Ј-C), 129.9 (2-C)a,
131.4 (7a-C)a, 132.7 (3a-C)a, 137.2 (7-C), 138.3 (3Ј-C), 146.2
(6Ј-C), 149.6 (5-C)b, 153.4 (2Ј-C)b and 155.9 [CO2C(CH3)3]; m/z
338 (Mϩ, 18%), 265 (4), 238 (100), 223 (34), 130 (11), 119 (13),
69 (54) and 57 (68).
2-(3-Methyl-2-pyridyl)-1H-indole 18a
tert-Butyl 2-(3-methyl-2-pyridyl)-1H-indole-1-carboxylate 17a
(256 mg, 0.83 mmol) was dissolved in dichloromethane (50 cm3)
and adsorbed onto silica gel 60 (70–230 mesh, 8 g). The flask
(CHO), 1583 and 1522 (ArC᎐C), 1448 (C–N) and 850 (ArH
᎐
oop); δH (400 MHz; CDCl3 and DMSO-d6; Me4Si) 2.39 (3H, s,
1710
J. Chem. Soc., Perkin Trans. 1, 2000, 1705–1713

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ArCH3), 7.25–7.31 (2H, m, 5-H and 6-H), 7.37 (1H, dd, J 4.3
and 7.7, 5Ј-H), 7.49–7.51 (1H, m, 4-H), 7.71 (1H, d, J 7.7,
4Ј-H), 8.29–8.31 (1H, m, 7-H), 8.58 (1H, d, J 4.3, 6Ј-H), 9.83
(1H, s, CHO) and 11.89 (1H, br s, NH); δC (100.625 MHz;
CDCl3 and DMSO-d6) 18.5 (ArCH3), 111.3 (5Ј-C)a, 114.8
(3-C)b, 120.9 (5-C)a, 121.8 (6-C)a, 123.0 (4Ј-C)a, 123.2 (4-C)a,
124.5 (2-C)b, 133.0 (3a-C)b, 135.4 (7a-C)b, 137.8 (7-C)c, 146.2
(6Ј-C)c, 146.3 (3Ј-C)d, 148.3 (2Ј-C)d and 185.5 (CHO); m/z 236
(Mϩ, 41%), 208 (62), 207 (100), 180 (10), 103 (11) and 89 (6).
5-Methoxy-1-methyl-2-(3-methyl-2-pyridyl)-1H-indole-3-carb-
aldehyde 13b
5-Methoxy-2-(3-methyl-2-pyridyl)-1H-indole-3-carbaldehyde
19b (93 mg, 0.35 mmol) was dissolved in THF (5 cm3) and
cooled to Ϫ78 ЊC. Potassium hexamethyldisilazide (KHMDS,
0.5 M solution in toluene, 1.1 cm3, 0.52 mmol) was added
dropwise and the reaction mixture stirred at Ϫ78 ЊC for 30 min.
Methyl iodide (0.05 cm3, 0.87 mmol) was added and the reac-
tion mixture stirred for a further 30 min at Ϫ78 ЊC. After this
time the mixture was warmed to room temperature and stirred
for 30 min. The mixture was then quenched with water (20 cm3)
and extracted with ethyl acetate (3 × 30 cm3). The organic
fractions were combined and dried (MgSO4) and the solvent
removed under reduced pressure. The crude residue was puri-
fied by chromatography (20–30% ethyl acetate–hexane) to
afford the product 13b (81 mg, 83%) as a clear oil (Found: Mϩ
280.1212. C15H10N2 requires M, 280.1212); νmax(film)/cmϪ1 2934
(ArC–H), 2832 (OCH3), 1655 (CHO), 1618, 1584 and 1526
5-Methoxy-2-(3-methyl-2-pyridyl)-1H-indole-3-carbaldehyde
19b
Phosphorus oxychloride (0.04 cm3, 0.46 mmol) was added
dropwise to dry DMF (0.14 cm3, 1.83 mmol) at 0 ЊC. The result-
ing mixture was warmed to room temperature and treated with
5-methoxy-2-(3-methyl-2-pyridyl)-1H-indole 18b (99 mg, 0.42
mmol) in DMF (3 cm3). The mixture was heated to 35 ЊC and
left stirring at this temperature under a nitrogen atmosphere for
1 h. After this time, ice was added and the mixture was made
basic with 2 M aqueous sodium hydroxide. The mixture was
then heated at reflux for 30 min. Once the mixture had cooled,
the organic material was extracted into chloroform (3 × 30 cm3)
and the combined organic extracts were dried (MgSO4) and
concentrated under reduced pressure. The resulting residue was
subjected to column chromatography (20% ethyl acetate–
hexane followed by 10% methanol–ethyl acetate) to afford the
product 19b (93 mg, 84%) as a pale yellow solid; mp 181–182 ЊC
(methanol) (Found: Mϩ 266.1053. C, 72.60; H, 5.30; N, 10.40%.
C16H14N2O2 requires M, 266.1055. C, 72.20; H, 5.30; N,
10.50%); νmax(CHCl3)/cmϪ1 3443 (NH), 3019 (ArC–H), 1653
(ArC᎐C), 1479 (C–N) and 797 (ArH oop); δ (200 MHz;
᎐
H
CDCl3; Me4Si) 2.25 (3H, s, ArCH3), 3.57 (3H, s, NCH3), 3.93
(3H, s, OCH3), 7.01 (1H, dd, J 2.5 and 8.9, 6-H), 7.31 (1H, d,
J 8.9, 7-H), 7.39 (1H, dd, J 4.8 and 7.8, 5Ј-H), 7.71 (1H, dd,
J 1.6 and 7.8, 4Ј-H), 7.88 (1H, d, J 2.5, 4-H), 8.64 (1H, dd, J 1.6
and 4.8, 6Ј-H) and 9.59 (1H, s, CHO); δC (100.625 MHz;
CDCl3) 18.9 (ArCH3), 30.8 (NCH3), 55.7 (OCH3), 103.4 (6-C)a,
110.7 (4-C)a, 114.4 (5Ј-C)a, 115.6 (3-C), 124.3 (7-C)a, 125.7
(2-C)b, 132.3 (3a-C)b, 134.7 (7a-C)b, 138.3 (4Ј-C), 147.5 (6Ј-C),
148.1 (2Ј-C and 3Ј-C), 156.9 (5-C)c and 185.3 (CHO); m/z 280
(Mϩ, 100%), 279 (7), 265 (19), 252 (49), 251 (86), 237 (42), 209
(16) and 160 (11).
(CHO), 1522 (ArC᎐C), 1423 (C–N), 1220 (C–O) and 772 (ArH
᎐
oop); δH (400 MHz; CDCl3 and DMSO-d6; Me4Si) 2.40 (3H, s,
ArCH3), 3.89 (3H, s, OCH3), 6.92 (1H, dd, J 2.5 and 8.8, 6-H),
7.35–7.40 (2H, m, 5Ј-H and 7-H), 7.71 (1H, d, J 7.5, 4Ј-H), 7.82
(1H, d, J 2.5, 4-H), 8.58 (1H, d, J 3.7, 6Ј-H), 9.81 (1H, s, CHO)
and 11.68 (1H, br s, NH); δC (50.32 MHz; CDCl3 and DMSO-
d6) 18.7 (ArCH3), 55.1 (OCH3), 102.5 (6-C)a, 112.3 (5Ј-C)a,
113.6 (4-C)a, 115.0 (3-C), 123.3 (7-C)a, 125.5 (2-C)b, 130.5 (7a-
C)b, 133.2 (3a-C)b, 138.0 (4Ј-C), 146.4 (6Ј-C), 148.6 (2Ј-C and
3Ј-C)c, 155.8 (5-C)c and 185.8 (CHO); m/z 266 (Mϩ, 86%), 251
(3), 238 (64), 237 (20), 223 (100) and 195 (38).
1-Benzyl-2-(3-methyl-2-pyridyl)-1H-indole-3-carbaldehyde 13c
2-(3-Methyl-2-pyridyl)-1H-indole-3-carbaldehyde 19a (158 mg,
0.67 mmol) was dissolved in THF (10 cm3) and cooled to
Ϫ78 ЊC. Potassium hexamethyldisilazide (KHMDS, 0.5 M
solution in toluene, 2.0 cm3, 1.00 mmol) was added dropwise
and the reaction mixture stirred at Ϫ78 ЊC for 30 min. Benzyl
bromide (0.12 cm3, 1.00 mmol) was added and the reaction
mixture stirred for a further 30 min at Ϫ78 ЊC. After this time
the mixture was warmed to room temperature and stirred for 30
min. The mixture was then quenched with water (20 cm3) and
extracted with diethyl ether (3 × 30 cm3). The organic fractions
were combined and dried (MgSO4) and the solvent removed
under reduced pressure. The crude residue was purified by
chromatography (10% methanol–ethyl acetate) to afford the
product 13c (162 mg, 77%) as a clear oil (Found: Mϩ 326.1422.
C22H18N2O requires M, 326.1419); νmax(film)/cmϪ1 3058 (ArC–
1-Methyl-2-(3-methyl-2-pyridyl)-1H-indole-3-carbaldehyde 13a
2-(3-Methyl-2-pyridyl)-1H-indole-3-carbaldehyde 19a (171 mg,
0.73 mmol) was dissolved in THF (5 cm3) and cooled to
Ϫ78 ЊC. Potassium hexamethyldisilazide (KHMDS, 0.5 M
solution in toluene, 2.2 cm3, 1.09 mmol) was added dropwise
and the reaction mixture stirred at Ϫ78 ЊC for 30 min. Methyl
iodide (0.11 cm3, 1.81 mmol) was added and the reaction mix-
ture stirred for a further 30 min at Ϫ78 ЊC. After this time the
mixture was warmed to room temperature and stirred for 30
min. The mixture was then quenched with water (20 cm3) and
extracted with diethyl ether (3 × 30 cm3). The organic fractions
were combined and dried (MgSO4) and the solvent removed
under reduced pressure. The crude residue was purified by
chromatography (10% methanol–ethyl acetate) to afford the
product 13a (168 mg, 93%) as a clear oil (Found: Mϩ 250.1094.
C16H14N2O requires M, 250.1106); νmax(film)/cmϪ1 3011 (ArC–
H), 1657 (CHO), 1611, 1576 and 1535 (ArC᎐C), 1458 (C–N)
᎐
and 750 (ArH oop); δH (400 MHz; CDCl3; Me4Si) 1.97 (3H,
s, ArCH3), 5.23 (2H, d, J 2.4, NCH2Ph), 6.90–6.92 (2H, m,
2 × ArH), 7.12–7.16 (3H, m, 3 × ArH), 7.28–7.35 (3H, m, 5Ј-H,
5-H and 6-H), 7.38–7.40 (1H, m, 4Ј-H), 7.55 (1H, ddd, J 0.6, 1.5
and 7.8, 4-H), 8.40–8.43 (1H, m, 7-H), 8.62 (1H, dd, J 1.2 and
4.7, 6Ј-H) and 9.67 (1H, s, CHO); δC (100.625 MHz; CDCl3)
18.7 (ArCH3), 47.6 (NCH2Ph), 110.5 (7-C), 116.0 (3-C), 122.1
(4-C), 123.2 (5Ј-C)a, 124.1 (6-C)a, 124.3 (5-C)a, 125.0 (2-C),
126.7 (2 × ArCH), 127.7 (ArCH), 128.5 (2 × ArCH), 135.0
(3a-C)b, 136.0 (ArC)b, 138.2 (4Ј-C), 147.4 (6Ј-C), 147.7 (3Ј-C)c,
148.0 (2Ј-C)c and 185.3 (CHO); m/z 326 (Mϩ, 72%), 325 (4), 311
(26), 298 (11), 297 (24), 235 (100), 221 (27), 207 (44) and 91 (66).
H), 1655 (CHO), 1612, 1579 and 1535 (ArC᎐C), 1468 (C–N)
᎐
and 753 (ArH oop); δH (200 MHz; CDCl3; Me4Si) 2.21 (3H, s,
ArCH3), 3.57 (3H, s, NCH3), 7.33–7.43 (4H, m, 4-H, 5-H, 5Ј-H
and 6-H), 7.71 (1H, dd, J 0.9 and 7.8, 4Ј-H), 8.36–8.42 (1H, m,
7-H), 8.63 (1H, dd, J 0.9 and 4.8, 6Ј-H) and 9.64 (1H, s, CHO);
δC (100.625 MHz; CDCl3) 18.9 (ArCH3), 30.7 (NCH3), 109.8
(7-C), 115.8 (3-C), 122.2 (5-C)a, 123.2 (6-C)a, 124.0 (4-C)a, 124.4
(5Ј-C)a, 125.0 (2-C)b, 134.8 (3a-C)b, 137.4 (7a-C)b, 138.3 (4Ј-C),
147.5 (6Ј-C), 148.0 (2Ј-C)c, 148.1 (3Ј-C)c and 185.3 (CHO); m/z
250 (Mϩ, 100%), 249 (6), 235 (9), 222 (45), 221 (100), 207 (22)
and 130 (17).
11-Methyl-11H-pyrido[2,3-a]carbazole 20a
1-Methyl-2-(3-methyl-2-pyridyl)-1H-indole-3-carbaldehyde 13a
(80 mg, 0.32 mmol) was dissolved in dry DMF (15 cm3). Potas-
sium tert-butoxide (143 mg, 1.27 mmol) was added to the
reaction mixture, which was heated under nitrogen at 80 ЊC and
irradiated with a high-pressure mercury lamp through a quartz
filter for 10 min. The reaction mixture was quenched with water
J. Chem. Soc., Perkin Trans. 1, 2000, 1705–1713
1711

View Article Online
(50 cm3) and the organic material extracted into diethyl ether
(3 × 50 cm3). The organic layer was dried with magnesium
sulfate and filtered. The diethyl ether was then evaporated
under reduced pressure to afford a pale residue which was
subjected to chromatography (20% ethyl acetate–hexane) to
afford the product 20a (58 mg, 78%) as a pale yellow solid; mp
129–130.5 ЊC (ethyl acetate–hexane) (Found: Mϩ, 232.1000.
C, 82.70; H, 5.20; N, 12.00%. C16H12N2 requires M, 232.1001.
C, 82.73; H, 5.20; N, 12.05%); νmax(CHCl3)/cmϪ1 3019 (ArC–H),
(1H, d, J 8.3, 6-H), 8.16 (1H, d, J 7.8, 7-H), 8.19 (1H, dd, J 1.7
and 8.2, 4-H), 8.20 (1H, d, J 8.3, 5-H) and 8.80 (1H, dd, J 1.7
and 4.2, 2-H); δC (100.625 MHz; CDCl3) 49.1 (NCH2Ph), 110.3
(10-C), 119.6 (6-C), 119.8 (3-C and 9-C)a, 120.0 (5-C)a, 121.4
(7a-C)b, 123.1 (10a-C)b, 125.4 (9-C), 126.8 (3 × ArCH), 127.8
(4a-C)b, 128.4 (2 × ArCH), 134.1 (6a-C)c, 136.1 (4-C), 139.2
(11a-C)c, 139.2 (ArCH)c, 140.5 (1a-C) and 147.6 (2-C); m/z 308
(Mϩ, 97%), 307 (32), 232 (21), 231 (100), 217 (16), 154 (14) and
91 (38).
1604 and 1522 (ArC᎐C), 1211, 772 (ArH oop); δ (200 MHz;
᎐
H
CDCl3; Me4Si) 4.66 (3H, s, NCH3), 7.29–7.34 (1H, m, 10-H),
7.34 (1H, dd, J 4.3 and 8.3, 3-H), 7.46 (1H, d, J 8.5, 6-H), 7.50–
7.53 (2H, m, 8-H and 9-H), 8.14 (1H, d, J 8.5, 5-H), 8.11–8.21
(2H, m, 4-H and 7-H) and 8.87 (1H, dd, J 1.8 and 4.3, 2-H);
δC (100.625 MHz; CDCl3) 30.8 (NCH3), 109.3 (10-C), 118.5
(6-C)a, 119.5 (3-C)a, 119.7 (5-C)a, 119.8 (7-C)a, 119.9 (9-C)a,
121.0 (7a-C)b, 122.6 (10a-C)b, 125.2 (8-C), 127.7 (4a-C)b, 134.4
(6a-C)c, 136.1 (4-C), 139.4 (11a-C)c, 140.9 (1a-C)c and 147.3
(2-C); m/z 232 (Mϩ, 75%), 231 (100), 204 (7), 116 (11) and
102 (8).
11H-Pyrido[2,3-a]carbazole 21
11-Benzyl-11H-pyrido[2,3-a]carbazole 20c (50 mg, 0.16 mmol)
in dry benzene (2.5 cm3) was added to aluminium trichloride
(87 mg, 0.65 mmol) at 0 ЊC. The reaction mixture was stirred
at 0 ЊC for 40 min, and then stirred for a further 2 h at room
temperature. After this time the reaction mixture was quenched
with water (10 cm3) and the organic material extracted into
ethyl acetate (3 × 15 cm3). The organic layer was washed succes-
sively with 5% aqueous sodium hydrogen carbonate (30 cm3)
and a saturated sodium chloride solution (30 cm3), dried with
magnesium sulfate and filtered. The diethyl ether was then
evaporated under reduced pressure and the crude residue was
subjected to chromatography (10–30% ethyl acetate–hexane) to
afford the desired product 21 (28 mg, 80%) as a white solid; mp
171–172 ЊC (toluene) (lit.,28 172–173 ЊC) (Found: Mϩ, 218.0843.
M, C15H10N2 requires M, 218.0844); νmax(CHCl3)/cmϪ1 3299
8-Methoxy-11-methyl-11H-pyrido[2,3-a]carbazole 20b
5-Methoxy-1-methyl-2-(3-methyl-2-pyridyl)-1H-indole-3-carb-
aldehyde 13b (76 mg, 0.27 mmol) was dissolved in dry DMF (15
cm3). Potassium tert-butoxide (122 mg, 1.08 mmol) was added
to the reaction mixture, which was heated under nitrogen at
80 ЊC and irradiated with a high-pressure mercury lamp
through a quartz filter for 10 min. The reaction mixture was
quenched with water (50 cm3) and the organic material
extracted into diethyl ether (3 × 50 cm3). The organic layer was
separated, dried with magnesium sulfate and filtered. The
diethyl ether was then evaporated under reduced pressure to
afford a pale residue which was subjected to chromatography
(5–10% ethyl acetate–hexane) to afford the desired product
20b (55 mg, 77%) as an off-white solid; mp 122–123 ЊC (ethyl
acetate–hexane) (Found: Mϩ, 262.1097. C, 77.40; H, 5.20; N,
10.20%. C17H14N2O requires M, 262.1106. C, 77.80; H, 5.40;
N, 10.70%); νmax(CHCl3)/cmϪ1 3019 (ArC–H), 1602, 1578 and
(NH), 3030 (ArC–H), 1611, 1591 and 1526 (ArC᎐C), 1373
᎐
(C–N) and 754 (ArH oop); δH (400 MHz; CDCl3; Me4Si)
7.21–7.44 (3H, m, 8-H, 9-H and 10-H), 7.46 (1H, dd, J 4.3 and
8.2, 3-H), 7.57 (1H, d, J 8.5, 6-H), 8.15 (1H, dd, J 0.5 and 7.9,
7-H), 8.21 (1H, d, J 8.5, 5-H), 8.31 (1H, dd, J 1.6 and 8.2, 4-H),
8.93 (1H, dd, J 1.6 and 4.3, 2-H) and 11.60 (1H, br s, NH); δC
(100.625 MHz; CDCl3) 111.6 (10-C), 118.5 (9-C)a, 119.7 (3-C)a,
120.2 (6-C)a, 120.4 (7-C)a, 120.5 (8-C)a, 121.4 (7a-C)b, 123.7
(10a-C)b, 125.5 (5-C), 127.1 (4a-C)b, 135.4 (6a-C)c, 136.9 (4-C),
137.4 (11a-C)c, 139.3 (1a-C)c and 148.1 (2-C); m/z 218 (Mϩ,
100%), 217 (13), 201 (3) and 190 (6).
1522 (ArC᎐C), 1220 (C–O) and 772 (ArH oop); δH (200 MHz;
᎐
Acknowledgements
CDCl3; Me4Si) 3.92 (3H, s, NCH3), 4.61 (3H, s, OCH3), 7.14
(1H, dd, J 2.4 and 8.8, 9-H), 7.33 (1H, dd, J 4.3 and 8.2, 3-H),
7.40 (1H, d, J 8.8, 10-H), 7.40 (1H, d, J 8.4, 6-H), 7.55 (1H, d,
J 2.4, 7-H), 8.07 (1H, d, J 8.4, 5-H), 8.16 (1H, dd, J 1.8 and 8.2,
4-H) and 8.85 (1H, dd, J 1.8 and 4.3, 2-H); δC (50.32 MHz;
CDCl3) 33.0 (NCH3), 56.0 (OCH3), 101.9 (7-C), 110.1 (10-C)a,
115.0 (9-C), 118.0 (6-C)a, 119.6 (3-C), 119.9 (5-C), 120.7
(7a-C)b, 122.8 (10a-C)b, 127.7 (4a-C)b, 134.8 (6a-C)c, 136.0 (4-C
and 11a-C)c, 139.5 (1a-C)c, 147.2 (2-C) and 154.0 (8-C); m/z 262
(Mϩ, 100%), 261 (28), 248 (10), 247 (56), 219 (32) and 218 (27).
This work was supported by the National Research Foundation
(NRF) and the University of the Witwatersrand. A. L. R.
would like to thank the AECI for additional financial support.
Mrs S. Heiss of this University and Dr P. Boshoff (Cape
Technikon) are thanked for recording NMR spectra and mass
spectra respectively.
References
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11-Benzyl-11H-pyrido[2,3-a]carbazole 20c
1-Benzyl-2-(3-methyl-2-pyridyl)-1H-indole-3-carbaldehyde 13c
(148 mg, 0.46 mmol) was dissolved in dry DMF (15 cm3).
Potassium tert-butoxide (205 mg, 1.83 mmol) was added to the
reaction mixture, which was heated under nitrogen at 80 ЊC and
irradiated with a high-pressure mercury lamp through a quartz
filter for 10 min. The reaction mixture was quenched with water
(50 cm3) and the organic material extracted into diethyl ether
(3 × 50 cm3). The organic layer was dried with magnesium sul-
fate and filtered. The diethyl ether was then evaporated under
reduced pressure to afford a pale residue which was subjected to
chromatography (5–10% ethyl acetate–hexane) to afford the
desired product 20c (105 mg, 75%) as a white solid; mp 110–
111 ЊC (ethyl acetate) (Found: Mϩ, 308.1317. C22H16N2 requires
M, 308.1314); νmax(CHCl3)/cmϪ1 3020 (ArC–H), 1573 and 1524
(ArC᎐C) and 787 (ArH oop); δ (400 MHz; CDCl ; Me Si) 6.66
᎐
H
3
4
(2H, s, NCH2Ph), 7.11–7.21 (5H, m, 5 × ArCH), 7.29 (1H, ddd,
J 0.9, 7.0 and 7.8, 8-H), 7.33 (1H, dd, J 4.2 and 8.2, 3-H), 7.42
(1H, ddd, J 1.0, 7.0 and 8.2, 9-H), 7.48 (1H, d, J 8.2, 10-H), 7.53
8 C. B. de Koning, J. P. Michael and A. L. Rousseau, J. Chem. Soc.,
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1712
J. Chem. Soc., Perkin Trans. 1, 2000, 1705–1713

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1992, 57, 910; (e) E. M. Beccalli, A. Marchesini and T. Pilati,
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P. Malsher, Tetrahedron Lett., 1993, 34, 8361; (g) H.-J. Knölker,
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