Facile one-pot synthesis of 6-monosubstituted and 6,12-disubstituted 5,11-dihydroindolo[3,2-b]carbazoles and preparation of various functionalized derivatives

Article abstract of DOI:10.1021/jo0711337

(Chemical Equation Presented) A facile three-stage, one-pot approach for the synthesis of a variety of novel 6-monosubstituted and 6,12-disubstituted 5,11-dihydroindolo[3,2-b]carbazoles, in moderate to good yields (20-50%), has been developed, based on th

Full text of DOI:10.1021/jo0711337

Facile One-Pot Synthesis of 6-Monosubstituted and
6,12-Disubstituted 5,11-Dihydroindolo[3,2-b]carbazoles and
Preparation of Various Functionalized Derivatives
Rong Gu, Ahmed Hameurlaine, and Wim Dehaen*
Department of Chemistry, UniVersity of LeuVen, Celestijnenlaan 200F, B-3001 LeuVen, Belgium
wim.dehaen@chem.kuleuVen.be
ReceiVed May 29, 2007
A facile three-stage, one-pot approach for the synthesis of a variety of novel 6-monosubstituted and
6,12-disubstituted 5,11-dihydroindolo[3,2-b]carbazoles, in moderate to good yields (20-50%), has been
developed, based on the condensation of an indole and an aldehyde with a catalytic amount of iodine,
followed by an acid-catalyzed intramolecular cyclization with an ortho ester. The parent indolo[3,2-b]-
carbazoles (ICZs) could be converted to various functional derivatives. Both N-alkylation and N-arylation
were successfully accomplished, and azo-coupling, formylation, as well as bromination were performed
in a regioselective way leading to the formation of novel functional 6,12-disubstituted indolo[3,2-b]-
carbazoles. Starting from a monoformylated indolocarbazole, novel benzimidazolyl-substituted derivatives
were synthesized, while Suzuki cross-couplings on a monobrominated building block afforded a novel
pathway toward functionally arylated ICZs.
Introduction
on the optimization of their stability, processability, and charge
transport properties. Because of their thermal stabilities, intense
luminescence, and reversible oxidation processes, (oligo)-
carbazole compounds are widely being used in molecular
electronics.4 Much less attention has, however, been devoted
to the indolo[3,2-b]carbazole (ICZ) analogues, despite their
promising electronic characteristics, mainly because of the lack
of simple synthetic procedures toward variously functionalized
derivatives. In 1999, Hu et al. reported indolo[3,2-b]carbazole
derivative 1a, which shows an unusual atropisomerism and
excellent hole-transport properties in organic LEDs.5 In 2004,
the first organic FET (OFET) using ICZ 1b as an active layer
was successfully fabricated.6 N,N-Disubstituted indolo[3,2-b]-
carbazoles and polyindolo[3,2-b]carbazoles have also been
reported recently as new classes of high-performance p-channel
Over the years, interest in electro- and photoactive molecules
has greatly increased because of their utilization as active
components in a number of electronic devices, such as light
emitting diodes (LEDs),1 field effect transistors (FETs),2 and
photovoltaic cells.3 Organic materials are very attractive for
incorporation in such devices because of their good mechanical
properties, low cost, and tunable electrical and optical properties
(by structural modifications), and the main focus nowadays is
(1) (a) Burroughes, J. H.; Bradley, D. D. C.; Brown, A. R.; Marks, R.
N.; Mackay, K.; Friend, R. H.; Burns, P. L.; Holmes, A. B. Nature 1990,
347, 539-541. (b) Kulkarni, A. P.; Tonzola, C. J.; Babel, A.; Jenekhe, S.
A. Chem. Mater. 2004, 16, 4556-4573.
(2) (a) Dimitrakopoulos, C. D.; Malenfant, P. R. L. AdV. Mater. 2002,
14, 99-117. (b) Katz, H. E. Chem. Mater. 2004, 16, 4748-4756. (c)
Chabinyc, M. L.; Salleo, A. Chem. Mater. 2004, 16, 4509-4521.
(3) (a) Winder, C.; Saridifti, N. S. J. Mater. Chem. 2004, 14, 1077-
1086. (b) Coakley, K. M.; McGehee, M. D. Chem. Mater. 2004, 16, 4533-
4542.
(5) Hu, N. X.; Xie, S.; Popovic, Z.; Ong, B.; Hor, A. M. J. Am. Chem.
Soc. 1999, 121, 5097-5098.
(6) Wakim, S.; Bouchard, J.; Simard, M.; Drolet, N.; Tao, Y.; Leclerc,
M. Chem. Mater. 2004, 16, 4386-4388.
(4) (a) Sonntag, M.; Strohriegl, P. Chem. Mater. 2004, 16, 4736-4742.
(b) Kim, Y. E.; Kwon, Y. S.; Lee, K. S.; Park, J. W. Mol. Cryst. Liq. Cryst.
2004, 424, 153-158. (c) Brunner, K.; Van Dijken, A.; Bo¨rner, H.;
Bastiaansen, J. J. A. M.; Kiggen, N. M. M.; Langeweld, B. M. W. J. Am.
Chem. Soc. 2004, 126, 6035-6042. (d) Lygaitis, R.; Grazulevicius, J. V.;
Gaidelis, V.; Jankauskas, V.; Sidaravicius, J.; Tokarski, Z.; Jubran, N. Mol.
Cryst. Liq. Cryst. 2005, 427, 95-106.
(7) (a) Wu, Y. L.; Li, Y. N.; Gardner, S.; Ong, B. S. J. Am. Chem. Soc.
2005, 127, 614-618. (b) Li, Y. N.; Wu, Y. L.; Gardner, S.; Ong, B. S.
AdV. Mater. 2005, 17, 849-853. (c) Blouin, N.; Michaud, A.; Wakim, S.;
Boudreault, P. T.; Leclerc, M.; Vercelli, B.; Zecchin, S.; Zotti, G. Macromol.
Chem. Phys. 2006, 207, 166-174. (d) Blouin, N.; Leclerc, M.; Vercelli,
B.; Zecchin, S.; Zotti, G. Macromol. Chem. Phys. 2006, 207, 175-182. (e)
Li, Y.; Wu, Y. L.; Ong, B. S. Macromolecules 2006, 39, 6521-6527.
10.1021/jo0711337 CCC: $37.00 © 2007 American Chemical Society
Published on Web 08/15/2007
J. Org. Chem. 2007, 72, 7207-7213
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Gu et al.
SCHEME 1. Synthesis of Monosubstituted ICZ 4c
semiconductors, and they could be used to fabricate high-
mobility organic thin-film transistors (OTFTs).7
SCHEME 2. Synthesis of 6-Monosubstituted and
6,12-Disubstituted ICZs
Indolo[3,2-b]carbazoles have also gained significant impor-
tance because of their high affinity to the receptor for 2,3,7,8-
tetrachlorodibenzo-p-dioxin 2 (TCDD), which is called aryl
hydrocarbon or Ah receptor and involved in organogenesis, in
detoxification of endo- and xenobiotics, and in mediating diverse
organ-specific toxic responses of dioxins.8 6-Formylindolo[3,2-
b]carbazole (1c) and 6,12-diformylindolo[3,2-b]carbazole (1d)
have been demonstrated as extremely efficient ligands for the
Ah receptor, especially ICZ 1c which binds 5-8 times as strong
to the receptor as TCDD itself.9
Over the decades, a number of methods for the preparation
of indolo[3,2-b]carbazoles have been developed,10 such as (i)
Pt-mediated cyclodehydrogenation of N,N′-diphenyl-p-
phenylenediamine,11a (ii) double Fischer indolization of cyclo-
hexane-1,4-dione bis(phenylhydrazone),11b (iii) condensation of
indole and formaldehyde in the presence of a strong acid, air,
and sensitizers,11c (iv) Lewis acid catalyzed dimerization of 1-(1-
benzotriazol-1-yl-alkyl)indoles,11d (v) intramolecular cyclization
of 2-(1H-indol-3-yl-methyl)-1H-indole carbaldehyde,11e (vi)
condensation of indole with aliphatic aldehydes under acidic
conditions,11f and (vii) cyclization of 3,3′-bis(indolyl)methanes11g
or 2,3′-bis(indolyl)methanes11h via an acid-catalyzed reaction
in the presence of triethyl orthoformate. However, most of these
methods involve multistep routines starting from indoles to
afford the corresponding ICZs in low overall yields. Moreover,
the poor solubility of these unsubstituted or symmetrically
disubstituted ICZs in organic solvents makes further modifica-
tions very difficult.9,12
coupling, formylation, and bromination. Regioselectively mono-
formylated and monobrominated ICZs were proven to be useful
starting materials for further modifications of the chromophore
structures, through the preparation of benzimidazolyl-substituted
ICZs and Suzuki cross-coupling reactions, respectively.
Results and Discussion
In 2003, Bandgar and Shaikh reported the reaction of indoles
with various aldehydes or ketones using iodine as a catalyst to
afford 3,3′-bis(indolyl)methanes in excellent yields.14 On the
basis of their method, 3,3′-bis(indolyl)hexane (3) could be
obtained in 70% yield by condensation of indole and hexanal
in acetonitrile with a catalytic amount of I2 (0.1 equiv). When
compound 3 was treated with triethyl orthoformate in methanol
using either sulfuric acid or methanesulfonic acid as a catalyst
(Scheme 1), 6-pentyl-5,11-dihydroindolo[3,2-b]carbazole (4c)
was formed only in trace amounts (as evidenced by MS analysis
of the crude reaction mixture).
Interestingly, however, we discovered that, if the condensa-
tions of indole and aldehyde were carried out for a longer time
(14 h), the 3,3′-bis(indolyl)methanes isomerized to 2,3′-bis-
Recently, we have communicated our preliminary results on
an efficient three-stage one-pot approach toward 6-monosub-
stituted 5,11-dihydroindolo[3,2-b]carbazoles.13 The better solu-
bility of these asymmetrical ICZs allowed easier structural
modifications. Herein, we wish to report an extension of our
method to the synthesis of both 6-monosubstituted and asym-
metrically 6,12-disubstituted ICZs. Moreover, a variety of
functionalized 6-pentyl-5,11-dihydroindolo[3,2-b]carbazole de-
rivatives have been prepared via N-alkylation, N-arylation, azo-
1
(indolyl)methanes (as monitored by H NMR spectroscopy).
Such isomerizations, involving acid-induced cleavage of one
of the indoles from the 3,3′-bis(indolyl)methanes and formation
of an indoleinium intermediate followed by recombination, have
been described previously.15 Fourteen hours is indeed optimal
reaction time, and shorter or longer reaction time gave much
lower yields of 4c.13 Because of their instability, the 2,3′-isomers
were not purified after workup, and acid-catalyzed intramo-
lecular cyclizations were accomplished directly by treating the
crude 2,3′-isomers with different ortho esters in the presence
of sulfuric acid or methanesulfonic acid as a catalyst to afford
the corresponding 6-monosubstituted or 6,12-disubstituted ICZs
in acceptable overall yields (Scheme 2, Table 1).
(8) Bock, K. W.; Ko¨hle, C. Biochem. Pharmacol. 2006, 72, 393-404.
(9) Tholander, J.; Bergman, J. Tetrahedron 1999, 55, 6243-6260.
(10) For a review treating all literature about the synthesis of indolo-
[3,2-b]carbazoles until 2002, see: Kno¨lker, H. J.; Reddy, K. R. Chem. ReV.
2002, 102, 4303-4427.
(11) (a) Grotta, H. M.; Riggle, C. J.; Bearse, A. E. J. Org. Chem. 1961,
26, 1509-1511. (b) Robinson, B. J. Chem. Soc. 1963, 3097-3099. (c)
Bergman, J. Tetrahedron 1970, 26, 3353-3355. (d) Katritzky, A. R.; Li,
J.; Stevens, C. V. J. Org. Chem. 1995, 60, 3401-3404. (e) Wille, G.;
Mayser, P.; Thoma, W.; Monsees, T.; Baumgart, A.; Schmitz, H. J.; Schrenk,
D.; Polborn, K.; Steglich, W. Bioorg. Med. Chem. 2001, 9, 955-960. (f)
Tholander, J.; Bergman, J. Tetrahedron 1999, 55, 12577-12594. (g) Pindur,
U.; Muller, J. Arch. Pharmacol. 1987, 320, 280-282. (h) Wahlstrom, N.;
Stensland, B.; Bergman, J. Synthesis 2004, 8, 1187-1194.
When sulfuric acid was used as a catalyst, the overall yield
of the reaction was much lower than when methanesulfonic acid
was used (Table 1, entry 3). The optimum reaction conditions
that were developed for the cyclization step involved 1 equiv
(14) Bandgar, B. P.; Shaikh, K. A. Tetrahedron Lett. 2003, 44, 1959-
1961.
(15) Chakrabarty, M.; Basak, R.; Ghosh, N.; Harigaya, Y. Tetrahedron
2004, 60, 1941-1949.
(12) Black, D. S.; Ivory, A. J.; Kumar, N. Tetrahedron 1995, 51, 11801-
11808.
(13) Gu, R.; Hameurlaine, A.; Dehaen, W. Synlett 2006, 10, 1535-1538.
7208 J. Org. Chem., Vol. 72, No. 19, 2007

Synthesis of 5,11-Dihydroindolo[3,2-b]carbazoles
TABLE 1. Three-Stage, One-Pot Synthesis of 6-Monosubstituted
and 6,12-Disubstituted 5,11-Dihydroindolo[3,2-b]carbazoles
SCHEME 4. Synthesis of N-Monoarylated ICZ 7
entry
ICZ
R1
R2
yield (%)
1
2
3
4a
4b
4c
4d
4e
4f
methyl
isobutyl
pentyl
undecyl
phenyl
pentyl
pentyl
pentyl
H
H
H
H
H
methyl
ethyl
phenyl
46a
50a
47a (20)b
36a
4c
5d
6
20a
23a (10)b
30a (30)b
23b (9)a
7
8
4g
4h
both N-monosubstituted and asymmetrically N,N-disubstituted
ICZ derivatives (see later paragraphs).
a Using CH3SO3H as a catalyst. b Using H2SO4 as a catalyst. c Using
CH2Cl2 as solvent. d 30 min reaction time for the first step.
The Ullmann-type coupling of aryl halides with indolocar-
bazoles is a straightforward and inexpensive approach to obtain
N-arylated ICZs. Under the Ullmann coupling conditions we
have previously reported for the synthesis of oligocarbazoles,16
the desired N,N-diarylated products 5c-e (Scheme 3) were
obtained in good yields (53-70%).
SCHEME 3. Synthesis of N-Substituted ICZs
To synthesize an N-monoarylated derivative, ICZ 4c was
treated with only 1 equiv of iodobenzene under the same
Ullmann coupling conditions as described earlier. The reaction
gave in all cases only N,N-diarylated derivative 5c (together
with starting material 4c). To solve this problem, we designed
an alternative synthetic strategy. First, N-arylation of monotosyl
derivative 5b was performed to obtain the corresponding
monoarylated product 6 in 70% yield. Afterward, deprotection
of the p-tosyl group of 6 could be effected under basic conditions
to afford the desired N-monoarylated ICZ 7 in 95% yield
(Scheme 4).
Next, formylation of 4c was investigated under traditional
Vilsmeier conditions (POCl3/DMF). With a large excess of
Vilsmeier reagent, we observed both C- and N-formylated
products and purification of the complex reaction mixture was
not straightforward. However, on using only 1.2 equiv of
Vilsmeier reagent in 1,2-dichloroethane under reflux conditions,
6-formyl-12-pentyl-5,11-dihydroindolo[3,2-b]carbazole (8) was
selectively obtained and isolated in 50% yield (Scheme 5).
Benzimidazoles are very useful intermediates or subunits for
the development of molecules with pharmaceutical or biological
interest.17 Moreover, polybenzimidazoles have been reported as
electroactive and conducting polymers and widely studied as a
fuel-cell membrane.18 Using a known method reported by Black
et al.,19 we converted ICZ 8 to benzimidazoles 9a-c in
acceptable to good yields (48-70%) by reacting the aldehyde
with o-phenylenediamines in DMF at 120-150 °C (Scheme 5).
Similar to the C-formylation, azo-coupling reactions have also
been achieved regioselectively at the 12-position. On reacting
ICZ 4c with arenediazonium tetrafluoroborates in THF with
pyridine as a base, diaza-indolocarbazoles 10a-c were synthe-
sized in 28-42% yield (Scheme 6).
of 2,3′-bis(indolyl)methane, 1 equiv of the ortho ester, and 0.2
equiv of methanesulfonic acid in methanol at room temperature
for 14 h. On applying these conditions, a number of 6-mono-
substituted ICZs were obtained in comparable yields (36-50%),
except for 6-phenyl-substituted derivative 4e (20%, entry 5).
Aromatic aldehydes are less suitable for the formation of ICZs
because the corresponding 3,3′- and 2,3′-isomers are less stable,
quickly forming an insoluble precipitate that is difficult to
characterize. Asymmetrically 6,12-disubstituted ICZs were also
successfully obtained using orthoacetate, orthopropionate, or
orthobenzoate esters. Because of their lower reactivity compared
to that of the orthoformate ester, the overall yields were
somewhat lower than those obtained for the 6-monosubstituted
ICZs. To prepare ICZ 4h (R2 ) phenyl) in an acceptable yield
(23%), sulfuric acid had to be used (entry 8). Compounds 4a-e
were crystallized from the reaction medium. Investigation of
the mother liquor of the crystallization showed the presence of
a trace amount of further 4a-e together with highly colored
tarry material. However, no substantial amount of the indolo-
carbazoles 4a-e could be obtained after chromatographic
purification.
Compared to the previously reported unsubstituted or sym-
metrically substituted ICZs in literature, the better solubility of
these asymmetrical analogues 4a-h in apolar organic solvents
allows for easy further structural modifications. Since N-
alkylated derivatives of ICZs have attracted considerable
interest,6,7 we first explored N,N-disubstitution reactions. 6-Mono-
substituted ICZ 4c was chosen as the substrate of preference
for the investigation of ICZ derivatizations because of its high
yield and good solubility. N,N-Diethylation of 4c was performed
with bromoethane (4 equiv) in DMF at 70 °C with sodium
hydride as a base to afford compound 5a in 83% yield (Scheme
3). On the other hand, tosylation of 4c under similar reaction
conditions was found to occur at only one of the two nitrogen
atoms (opposite to the pentyl chain) to produce monotosylated
derivative 5b selectively in 60% yield (Scheme 3). Hence, the
reaction of 4c with p-toluenesulfonyl chloride is highly regi-
oselective. This remarkable result can be employed to prepare
(16) (a) Schaerlaekens, M.; Hendrickx, E.; Hameurlaine, A.; Dehaen,
W.; Persoons, A. Chem. Phys. 2002, 277, 43-52. (b) Hameurlaine, A.;
Dehaen, W. Tetrahedron Lett. 2003, 44, 957-959. (c) McClenaghan, N.
D.; Passalacqua, R.; Loiseau, F.; Campagna, S.; Verheyde, B.; Hameurlaine,
A.; Dehaen, W. J. Am. Chem. Soc. 2003, 125, 5356-5365. (d) Loiseau, F.;
Campagna, S.; Hameurlaine, A.; Dehaen, W. J. Am. Chem. Soc. 2005, 127,
11352-11363.
(17) Lin, S.; Yang, L. H. Tetrahedron Lett. 2005, 46, 4315-4319.
(18) (a) Kerres, J.; Ullrich, A.; Meier, F.; Ha¨ring, T. Solid State Ionics
1999, 125, 243-249. (b) Taj, S.; Sankarapapavinasam, S.; Ahmed, M. F.
J. Appl. Polym. Sci. 2000, 77, 112-115. (c) Kim, H. J.; Cho, S. Y.; An, S.
J.; Eun, Y. C.; Kim, J. Y.; Yoon, H. K.; Kweon, H. J.; Yew, K. H.
Macromol. Rapid Commum. 2004, 25, 894-897.
(19) Black, D. S. C.; Kumar, N.; Wong, L. C. H. Synthesis 1986, 474-
476.
J. Org. Chem, Vol. 72, No. 19, 2007 7209

Gu et al.
SCHEME 5. Synthesis of 6-Formyl ICZ 8 and
Benzimidazolyl Derivatives 9a-c
SCHEME 6. Synthesis of Arylazo Derivatives 10a-c
SCHEME 7. Synthesis of Dibromo ICZ 13
SCHEME 8. Synthesis of Monobrominated ICZ 15 and
Suzuki Coupling Reactions
In contrast to formylation and azo-coupling, bromination of
ICZ 4c with N-bromosuccinimide (NBS) or bromine was not
selective, and brominated products depended on the reaction
conditions, such as the amount of halogenation reagent and
reaction temperature. Tribrominated ICZ 11 and pentabromi-
nated ICZ 12 were obtained on treating 4c with 3 equiv of NBS
in dichloromethane (at room temperature, rt) or 5 equiv of Br2
in acetic acid (under reflux conditions), respectively.13 On the
other hand, the 2,8-dibrominated compound 13 was synthesized
with our one-pot approach starting from 5-bromoindole. Initially,
the reaction failed because of the very slow isomerization of
the corresponding 3,3′-bis(indolyl)hexane to the 2,3′-isomer.
However, when the more active hydroiodic acid was used as a
catalyst for the condensation reaction, dibromo derivative 13
was obtained in 26% overall yield (Scheme 7).
anhydrous ferric bromide in chloroform, and only a small
amount of the desired brominated compound 15 was observed
(as indicated by MS analysis). Because of the high hygroscopic-
ity of anhydrous ferric bromide, we envisaged that water was
the vital factor for the bromination of ICZ 4c. Therefore, the
reaction was carried out in a solvent mixture of chloroform and
water. The desired ICZ derivative 15 was now formed, together
with a trace amount of the dimer 14, but starting material 4c
was only partially consumed after reaction overnight. Finally,
under optimized reaction conditions (1 equiv of 4c, 3 equiv of
anhydrous FeBr3, homogeneous solvent mixture THF/H2O, 5:2),
the regioselectively brominated ICZ derivative 15 was obtained
in an excellent yield of 96% (Scheme 8).
Finally, Suzuki coupling reactions of ICZ 15 with various
phenylboronic acids were studied under standard reaction
conditions (0.5 mol % Pd(PPh3)4 as a catalyst and K2CO3 as a
base). The ideal solvent (mixture) for the reaction was explored,
for example, THF, THF/H2O (4:1), dioxane/EtOH (4:1), and
dioxane/H2O (4:1). The more polar and higher boiling point
solvent mixture dioxane/H2O (4:1) gave the best yields for the
desired products 4h and 16a,b (Scheme 8). Indeed, 4h is better
prepared by this method than by the condensation of 2,3′-bis-
(indolyl)hexane with triethyl orthobenzoate, and the interesting
Inspired by our preceding work on the regioselective chlo-
rination of ICZ 4c with anhydrous ferric chloride,20 we have
examined a similar method for the bromination of 4c with ferric
bromide. Our previous study in fact showed that a chlorinated
ICZ derivative was obtained with anhydrous ferric chloride,
whereas the use of ferric chloride hexahydrate resulted in an
oxidative dimerization. Contrary to our expectations, an opposite
result was obtained with anhydrous ferric bromide. The dimer-
ization product 14 was obtained as the main compound on using
(20) Gu, R.; Van Hecke, K.; Van Meervelt, L.; Toppet, S.; Dehaen, W.
Org. Biomol. Chem. 2006, 4, 3785-3789.
7210 J. Org. Chem., Vol. 72, No. 19, 2007

Synthesis of 5,11-Dihydroindolo[3,2-b]carbazoles
130.3 (CH), 133.7, 135.7, 137.5, 141.7, 141.9. HRMS (EI) calcd
for C24H16N2 [M]+, 332.1314; found, 332.1313.
dimer 16b would be very difficult to prepare with any other
reported methods.
6-Methyl-12-pentyl-5,11-dihydroindolo[3,2-b]carbazole (4f).
This compound was prepared according to General Procedure 1
using indole (0.50 g, 4.3 mmol), n-hexanal (0.21 g, 2.1 mmol),
and triethyl orthoacetate (0.35 g, 2.2 mmol). The reaction mixture
was purified by column chromatography on basic alumina (eluent
EtOAc/heptane, 1:4) to yield 4f (0.17 g, 23%) as an off-white solid.
Mp: 260-261 °C. IR (neat, cm-1): 3415, 2929, 2855, 1611, 1535,
Conclusions
In summary, an easy and efficient three-stage, one-pot
synthetic approach toward various 6-monosubstituted and 6,-
12-disubstituted 5,11-dihydroindolo[3,2-b]carbazoles has been
developed. Iodine was found to be a highly convenient catalyst,
promoting the electrophilic reaction of indoles with aliphatic
aldehydes under mild conditions to afford 2,3′-bis(indolyl)-
alkanes, which were converted to the corresponding 6-mono-
substituted or 6,12-disubstituted ICZs with ortho esters using
methanesulfonic acid as a catalyst. Enhanced solubility and
stability toward oxidative degradation of the novel ICZs allowed
for easy modification of the parent indolocarbazole skeleton.
Thus, ICZ 4c was substituted under different conditions,
including N-alkylation, N-tosylation, copper-catalyzed Ullmann
coupling, Vilsmeier reaction, azo-coupling, and bromination.
More complex functional ICZs, such as benzimidazole deriva-
tives 9a-c and dimer 16b, were obtained on the basis of
regioselectively C-formylated and brominated compounds.
1
1463, 1378. H NMR (300 MHz, DMSO-d6): δ 0.88 (t, J ) 7.27
Hz, 3H), 1.32-1.44 (m, 2H), 1.50-1.60 (m, 2H), 1.76-1.86 (m,
2H), 3.01 (s, 3H), 3.44-3.49 (m, 2H), 7.11-7.17 (m, 2H), 7.38 (t,
J ) 7.8 Hz, 2H), 7.50-7.53 (m, 2H), 8.11 (d, J ) 7.9 Hz, 1H),
8.24 (d, J ) 7.81 Hz, 1H), 10.93 (s, 1H), 10.97 (s, 1H). 13C NMR
(75 MHz, DMSO-d6): δ 14.4 (CH3), 14.8 (CH3), 22.7 (CH2), 28.5
(CH2), 29.3 (CH2), 32.0 (CH2), 110.3, 110.7 (CH), 110.8 (CH),
115.5, 117.9 (CH), 118.1 (CH), 120.0, 120.7, 122.2 (CH), 122.5
(CH), 123.2, 123.9, 125.1 (CH), 134.4, 135.0, 141.6. HRMS (EI)
calcd for C24H24N2 [M]+, 340.1940; found, 340.1944.
2,8-Dibromo-6-pentyl-5,11-dihydroindolo[3,2-b]carbazole (13).
This compound was prepared according to General Procedure 1
using 5-bromoindole (0.31 g, 1.6 mmol), n-hexanal (0.08 g, 0.8
mmol), four drops of HI as a catalyst, and triethyl orthoformate
(0.12 g, 0.8 mmol). The reaction mixture was purified by column
chromatography (silica, eluent EtOAc/heptane, 1:4) to yield 13 (0.10
g, 26%) as a slightly yellow solid. Mp: 265-267 °C. IR (neat,
cm-1): 3420, 3370, 1601, 1528, 1452, 1412, 1284. 1H NMR (300
MHz, DMSO-d6): δ 0.90 (t, J ) 6.75 Hz, 3H), 1.41-1.43 (m,
2H), 1.55 (br, 2H), 1.80 (br, 2H), 3.44 (br, 3H), 7.44-7.50 (m,
4H), 8.08 (s, 1H), 8.20 (s, 1H), 8.45 (s, 1H), 11.18 (s, 1H), 11.39
(s, 1H). 13C NMR (75 MHz, DMSO-d6): δ 14.4 (CH3), 22.5 (CH2),
28.5 (CH2), 28.7 (CH2), 31.9 (CH2), 99.2 (CH), 109.9, 112.7 (CH),
112.8 (CH), 119.0, 120.0, 122.3, 123.4 (CH), 124.4 (CH), 124.5,
125.0, 127.7 (CH), 128.3 (CH), 134.8, 136.4, 140.29, 140.36.
HRMS (EI) calcd for C23H2079Br2N2 [M]+, 481.9992; found,
481.9993.
N-Alkylation of 6-Pentyl-5,11-dihydroindolo[3,2-b]carbazole
(4c) (General Procedure 2). To a flame-dried, N2-flushed, round-
bottomed flask containing a solution of 4c (1.5 mmol) in dry THF
(10 mL), cooled to -20 °C, NaH (15 mmol) was added portionwise.
After the addition of alkyl halide (6 mmol), the mixture was allowed
to warm slowly to rt and was then heated at 70 °C overnight under
N2 atmosphere. The reaction mixture was cooled to rt, H2O was
added, and the solution was extracted with EtOAc. The organic
extracts were combined, washed with brine, dried over Na2SO4,
and concentrated in vacuo. The crude residue was purified by
column chromatography.
5,11-Diethyl-6-pentyl-5,11-dihydroindolo[3,2-b]carbazole (5a).
This compound was prepared according to General Procedure 2
using 4c (2.0 g, 6.1 mmol), NaH (60% in mineral oil, 2.4 g, 61
mmol), and bromoethane (2.7 g, 24.8 mmol). The crude residue
was dispersed in n-pentane (40 mL), and the resulting precipitate
was filtered off and carefully dried to give 5a (1.94 g, 83%) as a
yellow solid. Mp: 144-145 °C. IR (neat, cm-1): 2963, 2929, 1608,
1506, 1451, 1417. 1H NMR (300 MHz, DMSO-d6): δ 0.94 (t, J )
7.25 Hz, 3H), 1.33-1.51 (m, 8H), 1.62-1.68 (m, 2H), 1.88 (br,
2H), 3.61 (br, 2H), 4.49-4.59 (m, 4H), 7.16-7.24 (m, 2H), 7.43-
7.48 (m, 2H), 7.54-7.61 (m, 2H), 8.17 (d, J ) 7.93 Hz, 1H), 8.24
(s, 1H), 8.27 (d, J ) 7.69 Hz, 1H). 13C NMR (75 MHz, DMSO-
d6): δ 13.7 (CH3), 14.4 (CH3), 15.3 (CH3), 22.4 (CH2), 28.8 (CH2),
30.2 (CH2), 31.9 (CH2), 37.2 (CH2), 39.9 (CH2), 97.3 (CH), 108.9
(CH), 109.3 (CH), 118.5 (CH), 118.6 (CH), 120.0, 120.5 (CH),
121.1, 122.5 (CH), 122.6, 123.0, 124.2, 125.4 (CH), 126.3 (CH),
133.1, 135.7, 141.1, 142.5. HRMS (EI) calcd for C27H30N2 [M]+,
382.2409; found, 382.2406.
Experimental Section
One-Pot Approach for the Synthesis of 6-Monosubstituted
and 6,12-Disubstituted ICZs (General Procedure 1). To a
solution of indole (3.7 mmol) and the appropriate aldehyde (1.8
mmol) in CH3CN (5 mL), I2 (0.37 mmol) was added, and the
reaction mixture was stirred at rt for 14 h. Na2SO3 (aq, saturated)
was added, and the solution was extracted with EtOAc. After
concentration of the organic layer, the crude product and the
appropriate ortho ester (1.8 mmol) were dissolved in MeOH (2 mL).
Methanesulfonic acid (0.37 mmol) was added, and the reaction
mixture was stirred overnight at rt. The formed precipitate was
filtered off, carefully dried in vacuum until constant weight, and,
if required, purified by column chromatography.
6-Isobutyl-5,11-dihydroindolo[3,2-b]carbazole (4b). This com-
pound was prepared according to General Procedure 1 using indole
(0.43 g, 3.7 mmol), 3-methyl butyraldehyde (0.16 g, 1.8 mmol),
and triethyl orthoformate (0.27 g, 1.8 mmol). The precipitate was
filtered off and carefully dried to yield 4b (0.29 g, 50%) as an
off-white solid. Mp: 294-296 °C. IR (neat, cm-1): 3447, 3401,
2950, 2863, 1612, 1583, 1526, 1459. 1H NMR (300 MHz, DMSO-
d6): δ 1.05 (d, J ) 6.3 Hz, 6H), 2.27-2.31 (m, 1H), 3.40 (br,
2H), 7.09-7.18 (m, 2H), 7.34-7.39 (m, 2H), 7.47-7.51 (m, 2H),
7.98 (s, 1H), 8.10-8.18 (m, 2H), 10.87 (s, 1H), 11.06 (s, 1H). 13
C
NMR (75 MHz, DMSO-d6): δ 23.2 (CH3), 29.2 (CH3), 37.7 (CH2),
98.9 (CH), 111.2 (CH), 111.4 (CH), 118.1, 118.3 (CH), 118.5 (CH),
121.1 (CH), 121.3, 122.9 (CH), 123.5, 123.6, 125.6 (CH), 126.2
(CH), 135.5, 136.4, 142.0, 142.1. HRMS (EI) calcd for C22H20N2
[M]+, 312.1627; found, 312.1621.
6-Phenyl-5,11-dihydroindolo[3,2-b]carbazole (4e). This com-
pound was prepared according to General Procedure 1 using indole
(0.46 g, 3.9 mmol), benzaldehyde (0.21 g, 1.9 mmol), and triethyl
orthoformate (0.29 g, 1.9 mmol). The first step was carried out at
rt for 30 min. The precipitate was filtered off and carefully dried
to yield 4e (0.13 g, 20%) as a brown solid. Mp: 278-280 °C. IR
(neat, cm-1): 3397, 1611, 1528, 1456. 1H NMR (300 MHz, DMSO-
d6): δ 6.86 (t, J ) 7.49 Hz, 1H), 7.12 (d, J ) 7.92 Hz, 1H), 7.17
(t, J ) 7.49 Hz, 1H), 7.32 (t, J ) 7.32 Hz, 1H), 7.38 (t, J ) 7.40
Hz, 1H), 7.48-7.51 (m, 2H), 7.64-7.77 (m, 5H), 8.20 (s, 1H),
8.26 (d, J ) 7.75 Hz, 1H), 10.48 (s, 1H), 11.22 (s, 1H). 13C NMR
(75 MHz, DMSO-d6): δ 100.1 (CH), 110.8 (CH), 111.4 (CH), 117.6
(CH), 118.0, 118.1 (CH), 120.3, 120.6 (CH), 121.6 (CH), 122.6,
122.87, 122.93, 125.5 (CH), 125.8 (CH), 128.3 (CH), 129.6 (CH),
N-Arylation of 6-Pentyl-5,11-dihydroindolo[3,2-b]carbazole
(4c) via Ullmann Coupling (General Procedure 3). A solution
of 4c (1 mmol), K2CO3 (2 mmol), iodoarene (4 mmol), and copper
bronze (2.4 mmol) in o-dichlorobenzene (7 mL) was heated
J. Org. Chem, Vol. 72, No. 19, 2007 7211

Gu et al.
overnight at 190 °C. The reaction mixture was allowed to cool to
rt, and CHCl3 (20 mL) was added. The mixture was filtered, and
the filtrate was concentrated. To the residue, MeOH (20 mL) was
added, and the formed precipitate was filtered off and purified by
column chromatography.
125.9 (CH), 126.8 (CH), 129.4, 134.2, 136.3, 141.9, 189.8. HRMS
(EI) calcd for C24H22N2O[M]+, 354.1732; found, 354.1742.
Synthesis of Benzimidazole Derivatives of 6-Pentyl-5,11-
dihydroindolo[3,2-b]carbazole (4c) (General Procedure 4). A
solution of 8 (0.42 mmol) and the appropriate o-phenylenediamine
(0.64 mmol) in DMF (5 mL) was heated at 120 °C for 14 h under
a N2 atmosphere. After removal of the solvent, the crude residue
was purified by column chromatography.
6-Pentyl-5,11-diphenyl-5,11-dihydroindolo[3,2-b]carbazole (5c).
This compound was prepared according to General Procedure 3
using 4c (0.33 g, 1 mmol), K2CO3 (0.28 g, 2 mmol), iodobenzene
(0.82 g, 4 mmol), and copper bronze (1.5 g, 2.4 mmol). Column
chromatographic purification (silica, eluent EtOAc/heptane, 3:7)
yielded 5c (0.34 g, 70%) as a slightly yellow solid. Mp: 183-
185 °C. IR (neat, cm-1): 2922, 2854, 1592, 1496, 1448, 1415. 1H
NMR (300 MHz, CDCl3): δ 0.84 (t, 3H), 1.07-1.26 (m, 4H), 1.63
(br, 2H), 3.03 (br, 2H), 6.93 (d, J ) 8.10 Hz, 1H), 7.15-7.20 (m,
1H), 7.27-7.34 (m, 1H), 7.38-7.40 (m, 2H), 7.52-7.59 (m, 6H),
7.66-7.68 (m, 4H), 7.91 (s, 1H), 8.06 (d, J ) 7.51 Hz, 1H), 8.13
(d, J ) 8.01 Hz, 1H). 13C NMR (75 MHz, CDCl3): δ 14.6 (CH3),
22.9 (CH2), 28.8 (CH2), 29.4 (CH2), 32.6 (CH2), 97.8 (CH), 109.7
(CH), 110.4 (CH), 119.5 (CH), 119.7 (CH), 120.3 (CH), 121.8,
122.2, 123.1 (CH), 123.6, 124.0, 124.9, 125.6 (CH), 126.4 (CH),
127.9 (CH), 128.3 (CH), 128.8 (CH), 130.0 (CH), 130.4 (CH),
136.0, 137.9, 138.6, 141.6, 142.7, 145.3. HRMS (EI) calcd for
C35H30N2 [M]+, 478.2409; found, 478.2413.
6-Pentyl-5-phenyl-5,11-dihydroindolo[3,2-b]carbazole (7). The
first step was performed according to General Procedure 3 using
5b (0.40 g, 0.83 mmol), K2CO3 (0.23 g, 1.6 mmol), iodobenzene
(0.34 g, 1.7 mmol), and copper bronze (0.127 g, 2 mmol). Column
chromatographic purification (silica, eluent EtOAc/heptane, 3:7)
yielded 6 (0.32 g, 70%). A solution of 6 (0.32 g, 0.6 mmol) and 2
M KOH (in MeOH, 3 mL) in THF (25 mL) was heated at 55 °C
for 3 h. When the reaction mixture was cooled to rt, H2O was added,
and the solution was extracted with EtOAc. The organic extracts
were combined, washed with brine, dried over Na2SO4, and
concentrated in vacuo. The crude residue was purified by column
chromatography (silica, eluent EtOAc/heptane, 3:7) to afford 7 (0.22
g, 95%) as a slightly yellow solid. Mp: 229-231 °C. IR (neat,
cm-1): 3406, 2921, 2861, 1611, 1591, 1515, 1495, 1453, 1414.
1H NMR (300 MHz, DMSO-d6): δ 0.78 (t, 3H), 1.00 (br, 2H),
1.06-1.16 (m, 2H), 1.49 (br, 2H), 2.91 (br, 2H), 6.84 (d, J ) 8.01
Hz, 1H), 7.12 (d, J ) 7.45 Hz, 1H), 7.21 (d, J ) 7.38 Hz, 1H),
7.30-7.40 (m, 2H), 7.50-7.68 (m, 6H), 7.99 (d, J ) 7.99 Hz,
1H), 8.12 (s, 1H), 8.28 (d, J ) 7.59 Hz, 1H), 11.24 (s, 1H). 13C
NMR (75 MHz, DMSO-d6): δ 14.3, 22.2, 28.2, 28.8, 31.9, 98.9,
109.9, 110.9, 118.4, 119.4, 120.4, 120.5, 121.6, 122.3, 122.8, 123.1,
124.1, 125.3, 126.4, 128.8, 129.6, 130.1, 134.7, 136.3, 141.0, 141.6,
144.6. HRMS (EI) calcd for C29H26N2 [M]+, 402.2096; found,
402.2092.
6-(1H-Benzimidazol-2-yl)-12-pentyl-5,11-dihydroindolo[3,2-
b]carbazole (9a). This compound was prepared according to
General Procedure 4 using 8 (0.15 g, 0.42 mmol) and 1,2-
phenylenediamine (0.07 g, 0.65 mmol). Column chromatographic
purification (silica, eluent EtOAc/heptane, 3:7) yielded 9a (0.13 g,
70%) as a brown solid. Mp: 248-250 °C. IR (neat, cm-1): 3438,
3386, 2924, 2856, 1611, 1583, 1547, 1450, 1413. UV-vis (CH2-
1
Cl2) λmax (log ꢀ): 257 (4.5), 314 (4.5), 355 (4.3), 434 (4.1). H
NMR (300 MHz, DMSO-d6): δ 0.92 (t, 3H), 1.39-1.46 (m, 2H),
1.62 (br, 2H), 1.90 (br, 2H), 3.61 (br, 2H), 6.94 (t, J ) 7.44 Hz,
1H), 7.21 (t, J ) 7.38 Hz, 1H), 7.35-7.42 (m, 4H), 7.51-7.59
(m, 3H), 7.77 (br, 2H), 8.20 (d, J ) 7.8 Hz, 1H), 10.86 (s, 1H),
11.25 (s, 1H), 13.01 (s, 1H). 13C NMR (75 MHz, DMSO-d6): δ
14.4 (CH3), 22.7 (CH2), 28.8 (CH2), 29.1 (CH2), 32.0 (CH2), 103.9,
111.2 (CH), 111.5 (CH), 118.0 (CH), 118.7 (CH), 120.3, 120.5,
120.9, 122.1 (CH), 122.2 (CH), 122.3, 122.5, 125.6 (CH), 126.0
(CH), 134.4, 135.2, 141.8, 149.6. HRMS (EI) calcd for C30H26N4
[M]+, 442.2158; found, 442.2154.
Azo-Coupling Reactions of 6-Pentyl-5,11-dihydroindolo[3,2-
b]carbazole (4c) (General Procedure 5). A solution of 4c (0.31
mmol) and pyridine (1.53 mmol) in THF (4 mL) was cooled to
-78 °C, and the appropriate arenediazonium tetrafluoroborate salt
(0.46 mmol) was added. The mixture was allowed to warm to rt
and stirred overnight. EtOAc was added, and the organic solution
was washed with brine, dried over Na2SO4, and concentrated in
vacuo. The crude residue was purified by column chromatography.
6-Pentyl-12-(phenyldiazenyl)-5,11-dihydroindolo[3,2-b]carba-
zole (10a). This compound was prepared according to General
Procedure 5 using 4c (0.10 g, 0.31 mmol), pyridine (0.12 mL, 1.53
mmol), and benzenediazonium tetrafluoroborate (0.09 g, 0.46
mmol). Purification by column chromatography (silica, eluent
EtOAc/heptane, 1:4) yielded 10a (0.055 g, 42%) as a red solid.
Mp: 264-266 °C. IR (neat, cm-1): 3431, 3381, 2916, 2862, 1602,
1564, 1517, 1453, 1323, 1295, 1210. UV-vis (CH2Cl2) λmax (log
1
ꢀ): 271 (4.5), 307 (4.4), 509 (4.2). H NMR (300 MHz, DMSO-
d6): δ 0.90 (t, 3H), 1.37-1.45 (m, 2H), 1.57-1.67 (m, 2H), 1.89
(br, 2H), 3.61 (m, 2H), 7.24-7.34 (m, 2H), 7.49 (t, J ) 7.59 Hz,
2H), 7.56 (t, J ) 7.21 Hz, 1H), 7.62 (d, J ) 8.12 Hz, 1H), 7.71 (t,
J ) 7.67 Hz, 2H), 7.90 (d, J ) 8.08 Hz, 1H), 8.21 (d, J ) 7.87
Hz, 1H), 8.33 (d, J ) 7.83 Hz, 2H), 8.71 (d, J ) 7.93 Hz, 1H),
11.45 (s, 1H), 11.79 (s, 1H). 13C NMR (75 MHz, DMSO-d6): δ
14.4 (CH3), 22.7 (CH2), 29.1 (CH2), 32.0 (CH2), 111.6 (CH), 113.0
(CH), 119.5 (CH), 120.4 (CH), 121.4, 121.7, 121.9, 122.2 (CH),
122.7 (CH), 125.4, 125.6 (CH), 125.8 (CH), 126.7 (CH), 129.0,
129.8 (CH), 130.3 (CH), 134.8, 141.6, 142.0, 153.9. HRMS (EI)
calcd for C29H26N4 [M]+, 430.2158; found, 430.2160.
12-Pentyl-5,11-dihydroindolo[3,2-b]carbazole-6-carbalde-
hyde (8). To a solution of 4c (2.5 g, 7.7 mmol) in 1,2-dichloroethane
(25 mL), DMF (0.71 mL, 9.2 mmol) was added, and subsequently
POCl3 (0.84 mL, 9.2 mmol) was added dropwise at rt under N2
atmosphere. The mixture was heated at reflux overnight under N2
atmosphere. The mixture was cooled to rt, poured into ice water,
and extracted with EtOAc. The organic extracts were combined,
washed with brine, dried over Na2SO4, and concentrated in vacuo.
The crude residue was purified by column chromatography (silica,
eluent Et2O/heptane, 5:6) to give 8 (1.36 g, 50%) as a yellow solid.
Mp: 266-268 °C. IR (neat, cm-1): 3420, 3354, 2922, 2862, 1688,
1653, 1596, 1524, 1463. UV-vis (CH2Cl2) λmax (log ꢀ): 253 (4.5),
6-Bromo-12-pentyl-5,11-dihydroindolo[3,2-b]carbazole (15).
To a solution of 4c (0.5 g, 1.5 mmol) in a solvent mixture of THF
and H2O (5:2, 28 mL), anhydrous FeBr3 (1.36 g, 4.5 mmol) was
added portionwise under N2 atmosphere at rt. The mixture was
stirred for 20 h at rt. H2O (10 mL) was added, and the mixture was
extracted with EtOAc. The organic extracts were combined, washed
with brine (25 mL), dried over Na2SO4, and concentrated in vacuo.
The crude residue was purified by column chromatography (silica,
eluent EtOAc/heptane, 1:4) to give 15 as a white solid. Mp: 185-
187 °C. IR (neat, cm-1): 3419, 2929, 2867, 1611, 1585, 1525, 1464,
1404, 1323, 743. UV-vis (CH2Cl2) λmax (log ꢀ): 276 (4.7), 331
1
315 (4.3), 382 (4.3), 451 (4.0). H NMR (300 MHz, DMSO-d6):
δ 0.88 (t, 3H), 1.34-1.42 (m, 2H), 1.58 (br, 2H), 1.84 (br, 2H),
3.56-3.62 (m, 2H), 7.19 (t, J ) 7.48 Hz, 1H), 7.27 (t, J ) 7.47
Hz, 1H), 7.42-7.51 (m, 2H), 7.64 (d, J ) 8.08 Hz, 1H), 7.82 (d,
J ) 8.08 Hz, 1H), 8.16 (d, J ) 7.80 Hz, 1H), 8.54 (d, J ) 8.11
Hz, 1H), 11.32 (s, 1H), 11.53 (s, 1H), 11.82 (s, 1H). 13C NMR (75
MHz, DMSO-d6): δ 14.4 (CH3), 22.6 (CH2), 28.9 (CH2), 29.2
(CH2), 31.9 (CH2), 110.8, 111.9 (CH), 112.5 (CH), 119.2 (CH),
119.9 (CH), 120.9, 121.5, 121.6, 121.7, 122.1 (CH), 125.0 (CH),
1
(4.9), 398 (4.9). H NMR (300 MHz, DMSO-d6): δ 0.88 (t, 3H),
1.31-1.41 (m, 2H), 1.55-1.58 (m, 2H), 1.82 (br, 2H), 3.47-3.52
(m, 2H), 7.18-7.24 (m, 2H), 7.41-7.49 (m, 2H), 7.58 (d, J )
8.15 Hz, 1H), 7.62 (d, J ) 8.09 Hz, 1H), 8.14 (d, J ) 7.88 Hz,
7212 J. Org. Chem., Vol. 72, No. 19, 2007

Synthesis of 5,11-Dihydroindolo[3,2-b]carbazoles
1H), 8.69 (d, J ) 7.97 Hz, 1H), 11.16 (s, 1H), 11.28 (s, 1H). 13C
NMR (75 MHz, DMSO-d6): δ 14.4 (CH3), 22.7 (CH2), 28.4 (CH2),
29.1 (CH2), 31.9 (CH2), 93.3, 111.2 (CH), 111.6 (CH), 118.1 (CH),
118.3, 119.0 (CH), 119.8, 121.1, 121.9 (CH), 122.5 (CH), 123.1,
125.8 (CH), 126.3 (CH), 134.4, 135.0, 141.6. HRMS (EI) calcd
for C23H21BrN2 [M]+, 404.0888; found, 404.0910.
3H), 1.39-1.46 (m, 2H), 1.58-1.65 (m, 2H), 1.86 (br, 2H), 3.52-
3.57 (m, 2H), 6.81 (t, J ) 7.58 Hz, 1H), 7.05 (d, J ) 7.85 Hz,
1H), 7.16 (t, J ) 7.34 Hz, 1H), 7.26-7.37 (m, 2H), 7.48-7.50
(m, 2H), 7.59-7.72 (m, 5H), 8.15 (d, J ) 7.92 Hz, 1H), 10.43 (s,
1H), 11.06 (s, 1H). 13C NMR (75 MHz, DMSO-d6): δ 14.5 (CH3),
22.7 (CH2), 28.7 (CH2), 29.2 (CH2), 32.1 (CH2), 110.9 (CH), 111.4
(CH), 115.4, 117.5 (CH), 117.7, 118.3 (CH), 120.0, 120.3, 121.6
(CH), 122.1 (CH), 122.78, 122.84, 125.1 (CH), 125.4 (CH), 128.1
(CH), 129.5 (CH), 130.5 (CH), 134.0, 134.4, 137.6, 141.7, 141.9.
HRMS (EI) calcd for C29H26N2 [M]+, 402.2096; found, 402.2096.
Suzuki Coupling of Arylboronic Acids with 6-Bromo-12-
pentyl-5,11-dihydroindolo[3,2-b]carbazole (15) (General Pro-
cedure 6). A solution of 15 (0.49 mmol), arylboronic acid (1 mmol),
K2CO3 (1.2 mmol), and Pd(PPh3)4 (2.5 µmol) in a mixture of
dioxane and H2O (4:1, 10 mL) was degassed and flushed with N2
and then heated at reflux overnight. After removal of the solvents,
the reaction mixture was dissolved in EtOAc and washed with brine.
The organic fraction was dried over Na2SO4 and concentrated in
vacuo. The crude residue was purified by column chromatography.
6-Pentyl-12-phenyl-5,11-dihydroindolo[3,2-b]carbazole (4h).
This compound was prepared according to General Procedure 6
using 15 (0.10 g, 0.25 mmol), phenylboronic acid (0.06 g, 0.5
mmol), K2CO3 (0.085 g, 0.6 mmol), and Pd(PPh3)4 (1.4 mg, 1.25
µmol). Purification by column chromatography (silica, eluent
EtOAc/heptane, 1:9) yielded 4h (0.072 g, 72%) as a slightly yellow
solid. Mp: 214-215 °C. IR (neat, cm-1): 3407, 2926, 2865, 1612,
1536, 1460, 1378, 1307. UV-vis (CH2Cl2) λmax (log ꢀ): 276 (4.6),
Acknowledgment. We thank the University of Leuven and
the Ministerie voor Wetenschapsbeleid for their continuing
support. G.R. is grateful for a Research Council Scholarship
obtained from the University of Leuven. We also acknowledge
Dr. Wouter Maes, Karel Duerinckx, and Bert Demarsin for their
kind help.
Supporting Information Available: Additional experimental
1
data and H NMR and 13C NMR spectra for all new compounds.
This material is available free of charge via the Internet at
http://pubs.acs.org.
1
333 (4.7), 401 (3.9). H NMR (300 MHz, DMSO-d6): δ 0.92 (t,
JO0711337
J. Org. Chem, Vol. 72, No. 19, 2007 7213