Synthesis of diindolocarbazoles by cadogan reaction: Route to ladder oligo(p-aniline)s

Article abstract of DOI:10.1021/jo049419o

Symmetric and nonsymmetric diindolocarbazoles were successfully synthesized for the first time by a Cadogan ring closure using N-alkyl-2,7-disubstituted carbazole precursors. Cyclization reaction on N-alkyl-2,7-di(2′- nitrophenyl) carbazole derivatives is

Full text of DOI:10.1021/jo049419o

Syn th esis of Diin d oloca r ba zoles by Ca d oga n Rea ction : Rou te to
La d d er Oligo(p-a n ilin e)s
J immy Bouchard, Salem Wakim, and Mario Leclerc*
Department of Chemistry, Universite´ Laval, Quebec City, QC, Canada, G1K 7P4
mario.leclerc@chm.ulaval.ca
Received April 7, 2004
Symmetric and nonsymmetric diindolocarbazoles were successfully synthesized for the first time
by a Cadogan ring closure using N-alkyl-2,7-disubstituted carbazole precursors. Cyclization reaction
on N-alkyl-2,7-di(2′-nitrophenyl) carbazole derivatives is not regioselective and produced a separable
mixture of symmetric and nonsymmetric diindolocarbazoles. A carbazole derivative with methyl
protective groups at the 1- and 8-positions was therefore used to obtain a symmetric ladder oligo-
(p-aniline) (compound 22). Optical and electrochemical properties of compound 22 indicate that its
neutral semiconducting form is stable in air. This novel class of electroactive ladder oligomers should
create new opportunities in micro- and nanoelectronics.
In tr od u ction
processability as well as high charge carrier mobility is
desirable.1,4 Organic synthesis allows a great flexibility
at the molecular scale to develop conjugated oligomers
having optimized physical and chemical properties for
the aimed applications. It could therefore be interesting
to develop pentacene-like oligomers that show a similar
coplanar structure and favorable packing geometry to-
gether with improved stability and processability. From
this point of view, synthetic ladder-type π-conjugated
molecules could be promising materials for OFET ap-
plications. Until now, only few examples of ladder-
conjugated oligomers containing fused-ring thiophenes
have been reported.8 Substituted anthradithiophenes
with a mixture of syn and anti isomers were also
prepared by Laquindanum and co-workers.9 These com-
pounds show moderate solubility and good solution
stability, but no attempt was made to characterize or
separate the syn and anti isomers. Sirringhaus and co-
workers10 reported also the synthesis of dibenzothieno-
bisbenzothiophene (DBTBT), but an inseparable mixture
of different regioisomers was obtained. Poor FET perfor-
mances are observed when DBTBT films contain a
mixture of different isomers. Their results prove that
isomeric purity is of first importance for achieving high
charge-transport mobility. Starting from this point, we
present here a new class of pentacene-like semiconduct-
ing organic materials using ladder electroactive oligo-
(p-aniline) derivatives (see Chart 1).
A great number of organic semiconducting materials
have been developed and tested for the fabrication of
organic field-effect transistors (OFET) during the past
20 years.1 Among all investigated p-type materials,
regioregular poly(3-alkylthiophene)s,2 oligothiophenes,3
oligofluorenes,4 oligo(2,6-anthrylene)s,5 and fused aro-
matic compounds such as pentacene6 have shown the best
performances up to now. In particular, pentacene6 has
received great attention since it shows mobilities up to 5
cm2 V-1 s-1 with on-off current ratios of about 108.
However, pentacene suffers from oxidative instability,
insolubility, and sensitivity to visible light, making it
unsuitable for practical electronic device applications.4,7
To address this problem, the design and synthesis of
novel organic semiconductors with good stability and
* Corresponding author. Phone: (481) 656-3452. Fax: (418) 656-
7916.
(1) Dimitrakopoulos, C. D.; Malenfant P. R. L. Adv. Mater. 2002,
14, 99.
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1996, 69, 4108. (b) Sirringhaus, H.; Tessler, N.; Friend, R. H. Science
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Fre`re, P.; Allain, M.; Bettignies, R.; Levillain, E.; Roncali, J . Adv.
Mater. 2003, 15, 306. (b) Dimitrakopoulos, C. D.; Furman, B. K.,
Graham, T.; Hedge, S.; Purushothaman, S. Synth. Met. 1998, 92, 47.
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V.; Bao, Z. Chem. Mater. 2003, 15, 1778.
Interestingly, depending upon the nature of the R and
R′ groups, it may be possible to develop amphiphilic
molecules that could lead to well-defined thin films
(5) Ito, K.; Suzuki, T.; Sakamoto, Y.; Kubota, D.; Inoue, Y.; Sato,
F.; Tokito, S. Angew. Chem. Int. Ed. 2003, 42, 1159.
(6) (a) Gundlach, D. J .; Lin, Y. Y.; J ackson, T. N.; Nelson, S. F.;
Schlom D. G. IEEE Electron Device Lett. 1997, 18, 87. (b) Lin, Y. Y.;
Gundlach, D. J .; Nelson, S. F.; J ackson, T. N. IEEE Electron Device
Lett. 1997, 18, 606. C) Meng, H.; Bendikov, M.; Mitchell, G.; Helgeson,
R.; Wudl, F.; Bao, Z.; Siegrist, T.; Kloc, C.; Chen, C.-H. Adv. Mater.
2003, 15, 1090. (d) Klauk, H.; Halik, M.; Zschieschang, U.; Schmid,
G.; Radlik, W.; Weber, W. J . Appl. Phys. 2002, 92, 5259. (e) Kelley, T.
W.; Muyres, D. V.; Baude, P. F.; Smith, T. P.; J ones, T. D. Mater. Res.
Soc. Symp. Ser. 2003, 771, 169.
(8) (a) Mazaki, Y.; Kobayashi, K. Tetrahedron Lett. 1989, 30, 3315.
(b) Wex, B.; Kaafarani, B. R.; Neckers, D. C. J . Org. Chem. 2004, 69,
2197. (c) Yamaguchi, S.; Xu, C.; Tamao, K. J . Am. Chem. Soc. 2003,
125, 13662.
(9) Laquindanum, J . G.; Katz, H. E.; Lovinger, A. J . J . Am. Chem.
Soc. 1998, 120, 664.
(10) Sirringhaus, H.; Friend, R. H.; Wang, C.; Leuninger, J .; Mu¨llen,
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10.1021/jo049419o CCC: $27.50 © 2004 American Chemical Society
Published on Web 07/16/2004
J . Org. Chem. 2004, 69, 5705-5711
5705

Bouchard et al.
CHART 1. Con ju ga ted La d d er Oligo(p-a n ilin e)s
SCHEME 1. Syn th esis of th e Dior th o Sym m etr ic Isom er s a n d Non sym m etr ic Isom er s
through Langmuir-Blodgett processing or self-assembly
procedures. Moreover, the use of organic conjugated
molecules, as molecular nanowires or transistors, has
recently received much attention.11 From this point of
view, the proposed ladder oligomers, bearing adequate
end groups, have the potential to make connections with
different nanoelectrodes and to operate as three-way
nanoconnectors or molecular transistors.
tives.13 Our first approach was based on precursors
bearing nitro groups on side phenyl groups such as
compounds 4 and 5. As shown in Scheme 1, these
precursors were obtained in three steps from 2,7-dibro-
mocarbazole14 (compound 1). N-Alkylation of compound
1 was performed by the action of 1-bromooctane with K2-
CO3 in hot DMF to give compound 2 in an 82% isolated
yield after simple crystallization in methanol. On the
basis of procedures developed for 2,7-bis(4,4,5,5-tetra-
methyl-1,3,2-dioxaborolan-2-yl)-9,9-dioctylfluorene,15 com-
pound 2 was then dilithiated by using n-butyllithium in
THF at a low temperature, followed by a reaction with
2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, to
give the desired compound 3 in satisfactory yields.
Then, a Suzuki coupling reaction was carried out on
Resu lts a n d Discu ssion
To achieve a general synthesis of this new class of
materials, we focused on the Cadogan12 procedure as the
final ring closure reaction on various N-alkyl-2,7-di-
phenylcarbazole precursors. As we recently reported, this
reaction was successfully utilized for obtaining a large
number of well-defined 2,7-disubstitued carbazole deriva-
(13) (a) Morin, J .-F.; Leclerc, M. Macromolecules 2001, 34, 4680. (b)
Zotti, G.; Schiavon, G.; Zecchin, S.; Morin, J .-F.; Leclerc, M. Macro-
molecules 2002, 35, 2122.
(14) (a) Patrick, D. A.; Boykin, D. W.; Wilson, W. D.; Tanious, F. A.;
Spychala, J .; Bender, B. C.; Hall, J . E.; Dykstra, C. C.; Ohemeng, K.
A.; Tidwell, R. R. Eur. J . Med. Chem. 1997, 32, 781. (b) Dierschke, F.;
Grimsdale, A. C.; Mu¨llen, K. Synthesis 2003, 2470.
(15) Ranger, M.; Rondeau, D.; Leclerc, M. Macromolecules 1997, 30,
7686.
(11) (a) Carroll, R. L.; Gorman, C. B. Angew. Chem. Int. Ed. 2002,
41, 4378. (b) Tour, J . M. Acc. Chem. Res. 2000, 33, 791. (c) Flatt, A.
K.; Yao, Y.; Maya, F.; Tour, J . M. J . Org. Chem. 2004, 69, 1752.
(12) (a) Cadogan, J . I. G.; Carmeron-Wood, M.; Makie, R. K.; Searle,
R. J . G. J . Chem. Soc. 1965, 4831. (b) Cadogan, J . I. G. Organophos-
phorus Reagents in Organic Synthesis; Academic Press Inc.: London,
1979; p 269.
5706 J . Org. Chem., Vol. 69, No. 17, 2004

Synthesis of Diindolocarbazoles by Cadogan Reaction
SCHEME 2. Syn th esis of N-Octyl-3,6-d in itr o-2,7-bis(2′-n itr op h en yl)ca r ba zole (Com p ou n d 14)
compound 3 with 1-bromo-2-nitrobenzene or with 4-bromo-
3-nitroanisole using a stable PdII(OAc)2 complex in
combination with 4 equiv of triphenylphosphine ligands
to lead to compounds 4 and 5 in good yields. The
reductive Cadogan ring closure reaction12 in hot triethyl
phosphite was finally performed on molecules 4 and 5.
As described in Scheme 1, a mixture of two regioisomers
was isolated in an 80% yield, but the desired ladder oligo-
(p-aniline) was not formed. Indeed, because of the free
rotation between phenyl and carbazole units, ortho and
para ring closure reactions are both possible, and con-
sequently three different regioisomers can be produced.
In the case of X ) H, the crude product contains a
developed by Velasco and co-workers,16 to give compound
11 in a 40% yield. The deprotection of the methoxy groups
into hydroxyl groups was performed13b with 1 M boron
tribromide at low temperatures to give compound 12,
quantitatively. Then, product 12 was transformed13b by
the action of DMAP and trifluoromethanesulfonic anhy-
dride in cold pyridine to compound 13 in an 84% yield.
The formation of the unclosed trimer 14 was achieved
by a Suzuki cross-coupling reaction on compound 13 with
commercially available 4-methoxyphenylboronic acid ac-
cording to a similar procedure to that already described
for the formation of compounds 4 and 5. Several attempts
to produce the desired oligomer by the reductive Cadogan
ring closure reaction of compound 14 with triethyl
phosphite were unsuccessful. However, compound 14 was
totally converted to give a multicomponent mixture (more
than 10 different products based on thin-layer chroma-
tography).
Following these results, we decided to prepare a new
precursor (molecule 21), with methyl groups at the 1- and
8-positions on the carbazole and nitro groups on the side
phenyl groups. The key step of this synthetic methodology
is the preparation of a N-alkyl-1,8-dimethyl-2,7-disub-
stituted carbazole. Effectively, as described in Scheme
3, compound 17 was synthesized in two steps from
compound 15.17 First of all, due to the ortho-orienting
effect of the nitrogen atom in the carbazole unit during
the halogen/metal permutation,18 compound 15 reacted
regioselectively with 2 equiv of n-BuLi to form the
corresponding 1,8-dilithiated species, which was then
quenched with iodomethane to lead to compound 16, in
a 64% isolated yield. It is important to perform this
reaction in a mixture of diethyl ether and THF (5:1) to
1
mixture with 85% (determined by H NMR based on the
integration of NH peaks of the crude material) of the
diortho symmetric isomer 6 and 15% of the nonsymmetric
isomer 7. The purification of these regioisomers was
performed by preparative thin-layer chromatography.
Only the major symmetric isomer 6 was isolated in a 35%
yield, nonsymmetric isomer 7 being not obtained in a
pure form. This result can be explained by the predomi-
nant ortho-orienting effect of the nitrogen atom, which
prevents the formation of the para-symmetric isomer.
The replacement of the hydrogen atoms by methoxy
groups produces the same regioisomers but with an
inverse ratio. Surprisingly, the nonsymmetric compound
9 was now the major isomer formed (85% determined by
1H NMR based on the integration of NH pics of the crude
material). A standard column chromatography technique
allowed us to obtain compound 9 in a 40% yield but failed
to isolate isomer 8, which was always contaminated with
compound 9. Only semipreparative HPLC techniques
gave a few milligrams of compound 8.
To obtain the formation of the targeted isomer, a new
approach, using as precursor a N-alkyl-2,7-disubstitued
carbazole derivative with nitro groups at the 3- and
6-positions, was developed. As shown in Scheme 2, the
3,6-dinitration of compound 1013b was performed by the
action of Cu(NO3)2‚2.5 H2O according to a procedure
(16) Dobarro, A.; Velasco, D.; Arnim, V.; Finkelmann, H. Macromol.
Chem. Phys. 1997, 198, 2563.
(17) Bouchard, J .; Wakim, S.; Leclerc, M. Synth. Commun. 2004,
34, 1.
(18) Organoalkali Chemistry, in Organometallics in Synthesis. A
manual, 2nd ed.; Schlosser, M., Ed.; J ohn Wiley & Sons: New York,
2002; p 86.
J . Org. Chem, Vol. 69, No. 17, 2004 5707

Bouchard et al.
SCHEME 3. Syn th esis of 5,8-Dih yd r o-13,15-d im eth yl-14-octyl-d iin d olo[3,2-b:2′,3′-h ]ca r ba zole (Com p ou n d
22)
ensure both the reactivity and the solubility of the
starting compound 15. Similar strategy was used to
remove bromine atoms at the 3- and 6-positions. First,
n-BuLi was used to form the 3,6-dilithiated species, which
was then quenched with distilled water to give compound
aliphatic protons) were doubled. The 13C NMR spectrum
was also intriguing, all aromatic and aliphatic carbons
being doubled. Restricted rotation around the aryl-aryl
bond (between phenyl and carbazole moieties) due to
nitro and methyl functions can probably lead to the
phenomenon of atropisomerism.21 However, the double
Cadogan ring closure was performed on compound 21 at
160 °C for 24 h, by the use of triethyl phosphite which
acted, at the same time, as reagent and solvent. A pale
yellow precipitate was formed when the reaction was
stopped. The crude product was then purified by column
chromatography to give the desired diindolocarbazole
1
17 in a good yield. H NMR spectrum of compound 17
contains two doublets in the aromatic region with a
coupling constant of 8.4 Hz, characteristic of two adjacent
aromatic protons. Thereafter, a standard deprotection
reaction using BBr3 in anhydrous dichloromethane was
achieved to give the corresponding 2,7-dihydroxy-1,8-
dimethylcarbazole 18 in an excellent yield. Compound
18 was treated with DMAP and trifluoromethanesulfonic
anhydride in cold pyridine to give compound 19. Boronic
esters can now be easily introduced at the 2,7-positions
on compound 19 by Masuda reaction19 using PdCl2(dppf)20
as the catalyst. Thus, compound 20 was synthesized in
a 69% isolated yield and can be used directly for the
Suzuki cross-coupling reaction with commercially avail-
able 1-bromo-2-nitrobenzene. A double Suzuki reaction
of 20 with 1-bromo-2-nitrobenzene was achieved under
standard conditions using air stable Pd(OAc)2 in combi-
nation with 4 equiv of triphenylphosphine ligands. After
column chromatography, compound 21 was isolated in a
1
(compound 22) in a 30% isolated yield. The H NMR and
13C NMR analyses confirmed the chemical structure of
compound 22. This product, soluble in common organic
solvents as THF, CH2Cl2, etc., offers the possibility to
develop different types of ladder oligo(p-aniline) deriva-
tives depending on the nature of the substituents that
can react with the free aromatic amine moieties.
Effect of the structure on the optical and electrochemi-
cal properties of these isomers was studied by comparing
the ortho (compound 6) and para (compound 22) sym-
metric isomers. The optical band gap for compounds 6
and 22 is 3.32 and 2.73 eV, respectively. This is in
agreement with structures determined by NMR analyses,
where a greater degree of conjugation for oligomer 22 can
be expected. Cyclovoltammetric measurements with com-
pounds 6 and 22 were also performed in THF solution
1
73% yield. Analysis of the H NMR spectrum of 21 shows
that signals of all protons (with the exception of some
(19) Murata, M.; Oyama, T.; Watanabe, S.; Masuda, Y. J . Org. Chem.
2000, 65, 164.
(20) Hayashi, T.; Konishi, M.; Kobori, Y.; Kumada, M.; Higuchi, T.;
Hirotsu, K. J . Am. Chem. Soc. 1984, 106, 158.
(21) Cammidge, A. N.; Cre´py, K. V. L. J . Org. Chem. 2003, 68, 6832.
5708 J . Org. Chem., Vol. 69, No. 17, 2004

Synthesis of Diindolocarbazoles by Cadogan Reaction
organic layers were washed with brine and dried over mag-
nesium sulfate. The solvent was removed by rotary evapora-
tion, and the residue was purified by crystallization in
methanol or by column chromatography (silica gel, 15% diethyl
ether in hexane as eluent) to provide 7.10 g of the title
(with 0.1 M tetrabutylammonium perchlorate). Com-
pound 22 shows a reversible oxidation at 0.70 V versus
SCE, while compound 6 shows a nonreversible oxidation
at 0.98 V versus SCE. These spectroscopic and electro-
chemical data indicate that the neutral semiconducting
form of both compounds 6 and 22 is stable in air.
1
compound as white crystals (67% yield): mp 168-169 °C; H
NMR (300 MHz, CDCl3) δ 8.13 (d, 2H, J ) 7.4 Hz), 7.89 (s,
2H), 7.69 (d, 2H, J ) 7.4 Hz), 4.39 (t, 2H, J ) 7.4 Hz), 1.90
(m, 2H), 1.41 (m, 24H), 1.30 (m, 10H), 0.88 (t, 3H, J ) 6.6
Hz); 13C NMR (75 MHz, CDCl3) δ 140.5, 125.09, 124.9, 120.0,
115.3, 83.8, 43.1, 32.0, 29.5, 29.4, 27.3, 25.1, 25.1, 22.8, 14.3;
HRMS m/z calculated for C32H47NO4B2 531.3691, found
531.3700.
Con clu sion
In summary, starting from N-alkyl-2,7-disubstituted
carbazoles, we have developed, for the first time, a
general route to new symmetric and nonsymmetric
diindolocarbazoles, using the Cadogan ring closure reac-
tion. This reductive reaction realized on N-alkyl-2,7-di-
(2′-nitrophenyl)carbazole derivatives is not regioselective
and produced a separable mixture of symmetric and
nonsymmetric diindolocarbazoles. Using a carbazole
derivative with methyl groups at the 1- and 8-positions
(compound 20), this reaction occurred regioregularly to
offer the symmetric compound 22. An attractive feature
of this synthetic approach is the wide variety of ladder
oligo(p-aniline)s that can be readily accessible from
carbazole 20 by the appropriate choice of aryl groups and
substituents. Preliminary studies of the spectroscopic and
electrochemical properties of this symmetric diindolocar-
bazole indicate that this new class of materials could
create new opportunities in micro- and nanoelectronics.
Utilization of the present compound as an organic semi-
conductive material in organic field-effect transistors as
well as the synthesis of longer oligomers and oligomers
with different side chain patterns are currently in
progress in our laboratory.
N-Octyl-2,7-bis(2′-n itr op h en yl)ca r ba zole (4). A two-
necked 25 mL flask, fitted with a condenser, was charged with
2.00 g (3.77 mmol) of 3, 1.50 g (7.46 mmol) of 1-bromo-2-
nitrobenzene, 9 mL of toluene, and 6 mL of K2CO3 2 M. The
resulting solution was degassed with a vigorous flow of argon
for 30 min, then 68 mg (0.30 mmol) of Pd(OAc)2 and 318 mg
(1.21 mmol) of PPh3 was added under argon, and the mixture
was heated under reflux for 48 h. After cooling to room
temperature, the mixture was put into 30 mL of distilled water
and extracted three times with CHCl3 (3 × 50 mL). The
combined organic fractions were dried over magnesium sulfate,
and the solvent was removed under reduced pressure to give
2.50 g of the crude material. Crystallization from MeOH
afforded 1.65 g of the title product as yellow needles (84%
yield): mp 120-121 °C; 1H NMR (400 MHz, acetone-d6) δ 8.25
(dd, 2H, J ) 8.0 and 0.6 Hz), 7.96 (dd, 2H, J ) 8.0 and 0.4
Hz), 7.79 (m, 2H), 7.68 (m, 6H), 7.62 (dd, 2H, J ) 1.6 and 0.6
Hz), 4.50 (t, 2H, J ) 7.2 Hz), 1.90 (m, 2H), 1.30 (m, 10H), 0.81
(t, 3H, J ) 6.9 Hz); 13C NMR (100 MHz, acetone-d6) δ 150.4,
141.4, 136.8, 135.6, 132.6 (2C), 128.7, 124.2, 122.5, 121.1,
119.5, 109.1, 43.0, 31.9, 29.5, 29.4, 29.2, 27.2, 22.7, 13.8; HRMS
m/z calculated for C32H31N3O4 521.2314, found 521.2310.
N-Octyl-2,7-bis(4′-m eth oxy-2′-n itr oph en yl)car bazole (5).
This compound was synthesized according to a similar proce-
dure as the one used for 4 using 2.00 g (3.76 mmol) of 3, 1.92
g (8.28 mmol) of 1-bromo-2-nitroanisole, 34 mg (0.15 mmol) of
Pd(OAc)2, 158 mg (0.60 mmol) of PPh3, 9 mL of toluene, and
6 mL of K2CO3 2 M. After 3 days, the resulting mixture was
poured into 50 mL of distilled water and extracted with ethyl
acetate (3 × 50 mL). The combined organic fractions were dried
over magnesium sulfate, and the solvent was removed under
reduced pressure. The crude material was passed through a
short column of silica gel using CHCl3 as eluent to remove
catalyst residues. Then, the compound was put in a hot
mixture of hexane/ethyl acetate (9:1) and sonicated for 2-3
min. After cooling to 0 °C, the solid was recovered by filtration
to provide 1.88 g of the title product as a yellow solid (86%
yield): mp 146-147 °C; 1H NMR (300 MHz, CDCl3) δ 8.11 (d,
2H, J ) 8.0 Hz), 7.49 (d, 2H, J ) 8.5 Hz), 7.39 (d, 2H, J ) 2.6
Hz), 7.31 (s, 2H), 7.17 (m, 4H), 4.26 (t, 2H, J ) 7.1 Hz), 3.93
(s, 6H), 1.86 (m, 2H), 1.30 (m, 10H), 0.85 (t, 3H, J ) 6.4 Hz);
13C NMR (75 MHz, CDCl3) δ 159.1, 150.1, 141.0, 134.9, 133.1,
129.4, 122.2, 120.7, 119.4, 118.5, 108.9, 108.3, 56.0, 43.2, 31.8,
29.3, 29.1, 28.9, 27.3, 22.6, 14.1; HRMS m/z calculated for
Exp er im en ta l P r oced u r es
N-Octyl-2,7-d ibr om oca r ba zole (2). A 100 mL flame-dried
flask was charged with 9.61 g (29.6 mmol) of 2,7-dibromocar-
bazole 1,14 8.18 g (59.2 mmol) of anhydrous K2CO3, 7.72 mL
(44.4 mmol) of 1-bromooctane, and 60 mL of anhydrous N,N-
dimethylformamide. The resulting mixture was stirred at 80
°C for 12 h under an inert atmosphere. The solution was
quenched with 150 mL of distilled water and extracted twice
(2 × 100 mL) with CHCl3. The combined organic layers were
washed with distilled water (5 × 50 mL) and dried over
magnesium sulfate, and the solvent was removed under
reduced pressure. Recrystallization from methanol afforded
10.6 g of the title compound as a white solid (82% yield): mp
1
66-67 °C; H NMR (400 MHz, CDCl3) δ 7.86 (d, 2H, J ) 8.3
Hz), 7.51 (d, 2H, J ) 1.6 Hz), 7.33 (dd, 2H, J ) 8.3 and 1.6
Hz), 4.16 (t, 2H, J ) 7.4 Hz), 1.82 (m, 2H), 1.30 (m, 10H), 0.89
(t, 3H, J ) 6.9 Hz); 13C NMR (100 MHz, CDCl3) δ 141.3, 122.4,
121.4, 121.2, 119.6, 111.9, 43.3, 31.7, 29.2, 29.1, 28.7, 27.1, 22.6,
14.1; HRMS m/z calculated for C20H23NBr2 435.0197, found
435.0201.
C
34H35N3O6 581.2526, found: 581.2514.
5,7-Dih yd r o-6-octyl-d iin d olo[2,3-a :3′,2′-i]ca r ba zole (6).
N-Octyl-2,7-bis(4,4,5,5-tetr a m eth yl-1,3,2-d ioxa bor ola n -
2-yl)ca r ba zole (3). In a 250 mL flame-dried two-necked flask,
equipped with a dropping funnel, 8.71 g (19.9 mmol) of 2 was
dissolved with 150 mL of freshly distilled THF. The resulting
solution was cooled at -78 °C and 16.7 mL (41.8 mmol) of
n-butyllithium (2.5 M in hexane) was added over 15-20 min
under a nitrogen atmosphere. The mixture was stirred at -78
°C for 1.5 h, warmed to 0 °C for 15 min, and cooled again at
-78 °C for 15 min. A total of 9.76 mL (47.8 mmol) of
2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane was added
rapidly to the solution, and then the resulting mixture was
allowed to warm to room temperature and was stirred for 12
h. The mixture was poured into 200 mL of distilled water and
then extracted with CHCl3 (3 × 100 mL). The combined
A 10 mL flame-dried flask, equipped with a condenser, was
charged with 100 mg (0.19 mmol) of 4 and 1.0 mL of triethyl
phosphite. The resulting mixture was heated under reflux
under nitrogen for 24 h, and then the excess of triethyl
phosphite was distilled off under reduced pressure. The 1H
NMR spectra of the crude material (80% yield) showed mainly
two compounds, 6 and 7, in a 5:1 ratio. Only compound 6 was
isolated on silica gel by preparative thin-layer chromatography
(40% ethyl acetate in hexane as eluent) as a pale yellow solid
(30 mg, 35% yield): mp 278-280 °C; 1H NMR (400 MHz,
Acetone-d6) δ 10.67 (s, 2H, NH), 8.18 (d, 2H, J ) 7.8 Hz), 8.03
(m, 4H), 7.62 (d, 2H, J ) 8.1 Hz), 7.37 (t, 2H, J ) 7.5 Hz),
7.23 (t, 2H, J ) 7.5 Hz), 5.29 (t, 2H, J ) 6.9 Hz), 1.98 (m, 2H),
J . Org. Chem, Vol. 69, No. 17, 2004 5709

Bouchard et al.
1.17 (m, 10H), 0.68 (t, 3H, J ) 6.9 Hz); 13C NMR (100 MHz,
acetone-d6) δ 140.2, 127.2, 126.2, 124.9, 124.5, 123.3, 121.9,
119.7, 119.7, 112.6, 112.2, 111.7, 47.1, 32.1, 31.8, 29.2, 26.2,
22.5, 13.6 (one aromatic carbon missing); HRMS m/z calculated
for C32H31N3 457.2518, found 457.2527.
mixture was extracted with dichloromethane (3 × 20 mL). The
organic layer was washed twice with brine and dried over
magnesium sulfate, and the solvent was removed under
reduced pressure to provide 93 mg (yield >99%) of the title
molecule as a yellow solid: mp 198-200 °C; 1H NMR (300
MHz, CDCl3) δ 11.19 (s, 2H), 8.75 (s, 2H), 6.93 (s, 2H), 4.13 (t,
2H, J ) 7.4 Hz), 1.85 (m, 2H), 1.32 (m, 10H), 0.87 (t, 3H, J )
6.5 Hz); 13C NMR (100 MHz, CDCl3) δ 155.7, 148.4, 128.9,
118.0, 116.9, 97.6, 44.1, 31.7, 29.2, 29.1, 28.1, 27.1, 22.5, 14.0;
HRMS m/z calculated for C20H23N3O6 401.1587, found 401.1590.
5,7-Dih yd r o-3,9-d im eth oxy-6-octyl-d iin d olo[2,3-a :3′,2′-
i]ca r ba zole (8) a n d 5,12-Dih yd r o-3,10-d im eth oxy-6-octyl-
d iin d olo[2,3-a :2′,3′-h ]ca r ba zole (9). These compounds were
synthesized according to a similar procedure as the one used
for 6 using 726 mg (1.40 mmol) of 5 and 5.7 mL of triethyl
phosphite. The resulting mixture was heated under reflux
under nitrogen for 24 h. After being cooled to room tempera-
ture, the mixture was put into hexane containing 4% of acetone
at 0 °C. The resulting precipitate was recovered by filtration
to provide 533 mg (crude yield ) 80%) of a mixture containing
mainly molecules 8 and 9 in a 1:5 ratio. The crude product
was purified by column chromatography (silica gel, 40% ethyl
acetate in hexane as eluent) to provide 290 mg of compound 9
as a pale yellow solid (40% yield). To obtain compound 8, a
small fraction (100 mg) of the crude product was purified by
semipreparative HPLC techniques using aqueous acetonitrile
(75%) as eluent. Fractions obtained were saturated with brine.
The organic layers were dried with anhydrous MgSO4, and the
solvent was removed under reduced pressure. (8): mp 270 °C
N-Octyl-3,6-d in itr o-2,7-bis(tr iflu or om eth a n esu lfon yl)-
ca r ba zole (13). A 50 mL flame-dried flask was charged with
1.62 g (4.03 mmol) of compound 12, 492 mg (4.03 mmol) of
4-(dimethylamino)pyridine, and 20 mL of anhydrous pyridine.
The mixture was stirred under inert atmosphere and cooled
to 0 °C, and 2.04 mL (12.1 mmol) of trifluoromethanesulfonic
anhydride was added dropwise. After 10 min, 5 mL of
anhydrous pyridine was added to dissolve the precipitate
formed during the addition of anhydride. The solution was
stirred at 0 °C for 1 h and at room temperature for 12 h. The
excess of anhydride was destroyed by a slow addition of 20
mL of distilled water. The mixture was extracted with CH2-
Cl2 (3 × 20 mL). The combined organic fractions were washed
successively with distilled water (5 × 50 mL), aqueous CuSO4
0.1 M (5 × 50 mL), brine (3 × 50 mL), and again with distilled
water (2 × 50 mL). The organic layer was dried over magne-
sium sulfate, and the solvent was removed under reduced
pressure. The crude product was purified by column chroma-
tography (silica gel, CH2Cl2 as eluent) to provide 2.25 g of the
title product as an off-white solid (84% yield): mp 158-160
°C; 1H NMR (300 MHz, CDCl3) δ 9.07 (s, 2H), 7.49 (s, 2H),
4.41 (t, 2H, J ) 7.0 Hz), 1.93 (m, 2H), 1.30 (m, 10H), 0.86 (t,
3H, J ) 6.6 Hz); 13C NMR (100 MHz, CDCl3) δ 143.9, 141.5,
135.8, 120.8, 120.7, 118.7, 105.6, 45.0, 31.5, 29.1, 28.9, 28.8,
27.2, 22.5, 13.9; HRMS m/z calculated for C22H21N3O10F6S2
665.0572, found 665.0583.
1
dec; H NMR (400 MHz, DMSO-d6) δ 11.37 (s, 2H, NH), 7.99
(d, 2H, J ) 8.4 Hz), 7.90 (d, 2H, J ) 8.2 Hz), 7.84 (d, 2H, J )
8.2 Hz), 7.17 (d, 2H, J ) 2.4 Hz), 6.82 (dd, 2H, J ) 8.4 Hz),
5.21 (t, 2H, J ) 6.6 Hz), 3.88 (s, 6H), 1.75 (m, 2H), 1.18 (m,
3H), 0.99 (m, 7H), 0.64 (t, 3H, J ) 7.0 Hz); 13C NMR (100 MHz,
DMSO-d6) δ 157.9, 141.0, 126.6, 125.3, 121.6, 121.1, 120.3,
117.5, 111.8, 111.7, 108.4, 95.2, 55.4, 46.1, 31.4, 31.2, 28.9, 28.6,
25.6, 22.1, 14.0; HRMS m/z calculated for C34H35N3O2 517.2729,
found 517.2737. (9): mp 250 °C dec; 1H NMR (400 MHz,
DMSO-d6) δ 11.18 (s, 1H, NH), 10.90 (s, 1H, NH), 8.19 (s, 1H),
8.07 (m, 2H), 8.01 (d, 1H, J ) 8.6 Hz), 7.95 (d, 1H, J ) 8.2
Hz), 7.79 (d, 1H, J ) 8.2 Hz), 7.16 (d, 1H, J ) 2.2 Hz), 6.96 (d,
1H, J ) 2.2 Hz), 6.82 (dd, 1H, J ) 8.5 and 2.3 Hz), 6.76 (dd,
1H, J ) 8.5 and 2.3 Hz), 4.85 (t, 2H, J ) 6.7 Hz), 3.88 (s, 3H),
3.85 (s, 3H), 1.84 (m, 2H), 1.21 (m, 10H), 0.73 (t, 3H, J ) 6.8
Hz); 13C NMR (100 MHz, DMSO-d6) δ 158.6, 158.0, 142.6,
141.2, 135.7, 135.6, 127.6, 124.7, 122.6, 122.3, 121.6, 121.0,
120.4, 119.7, 117.5, 116.8, 112.1, 110.4, 108.5, 106.8, 99.7, 98.8,
95.1, 94.5, 55.4, 55.4, 44.2, 31.4, 30.3, 30.1, 29.8, 26.3, 22.2,
14.1; HRMS m/z calculated for C34H35N3O2 517.2729, found
517.2721.
N-Octyl-3,6-din itr o-2,7-bis(2′-n itr oph en yl)car bazole (14).
This compound was synthesized according to a similar proce-
dure described previously for the synthesis of compound 4
using 1.84 g (2.77 mmol) of 13, 0.93 g (6.09 mmol) of
4-methoxyphenylboronic acid, 116 mg (0.44 mmol) of PPh3, 25
mg (0.11 mmol) of Pd(OAc)2, 23 mL of benzene, and 15.4 mL
of K2CO3 2 M (3 days at reflux; extraction with benzene). The
crude product was purified by column chromatography (silica
gel, 20% hexane in CH2Cl2 as eluent) to afford 1.30 g of the
title compound as yellow crystals (81% yield): mp 178-180
N-Octyl-3,6-d in itr o-2,7-d im eth oxyca r ba zole (11). In a
100 mL flask, 3.64 g (15.6 mmol) of Cu(NO3)2•2.5 H2O was
dissolved in a mixture of Ac2O (43.5 mL) and AcOH (21.6 mL)
at room temperature, and then 5.00 g (14.7 mmol) of 1013b was
added. The mixture was stirred for 30 min at room tempera-
ture and then poured into ice water (100 mL), neutralized with
10% NaOH, and extracted with CH2Cl2 (3 × 75 mL). The
combined organic fractions were washed twice with brine and
dried over magnesium sulfate, and the solvent was removed
under reduced pressure. The crude compound was purified by
crystallization in CHCl3/diethyl ether to afford 2.55 g of the
title product as a green-yellow solid (40% yield): mp 212-
214 °C; 1H NMR (300 MHz, CDCl3) δ 8.49 (s, 2H), 6.82 (s, 2H),
4.24 (t, 2H, J ) 7.1 Hz), 4.05 (s, 6H), 1.87 (m, 2H), 1.32 (m,
10H), 0.86 (t, 3H, J ) 6.4 Hz); 13C NMR (75 MHz, CDCl3) δ
153.5, 144.8, 134.3, 118.8, 114.9, 93.2, 56.9, 43.7, 31.7, 29.2,
29.0, 28.4, 27.1, 22.5, 14.0; HRMS m/z calculated for C22H27N3O6
429.1900, found 429.1905.
N-Octyl-3,6-d in itr o-2,7-d ih yd r oxyca r ba zole (12). A 10
mL flame-dried flask was charged under a nitrogen atmo-
sphere with 100 mg (0.23 mmol) of 11 and 2.3 mL of anhydrous
dichloromethane. The solution was cooled to -78 °C, and 1.15
mL (1.16 mmol) of boron tribromide (1 M in dichloromethane)
was added to the solution over 15 min. The resulting mixture
was stirred under nitrogen atmosphere at -78 °C for 45 min
and then quenched slowly (at -78 °C) with 2 mL of HCl 10%
(v/v) to destroy the excess of boron tribromide. The resulting
1
°C; H NMR (300 MHz, CDCl3) δ 8.74 (s, 2H), 7.36 (m, 6H),
7.02 (d, 4H, 8.5), 4.34 (t, 2H, J ) 7.2 Hz), 3.89 (s, 6H), 1.89
(m, 2H), 1.28 (m, 10H), 0.85 (t, 3H, J ) 6.6 Hz); 13C NMR (75
MHz, CDCl3) δ 159.6, 143.1, 136.2, 130.9, 129.3, 120.8, 118.4,
114.2, 112.0, 55.3, 43.9, 31.6, 29.1, 29.0, 28.8, 27.0, 22.5, 14.0
(one aromatic carbon missing); HRMS m/z calculated for
C
34H35N3O6 581.2526, found 581.2518.
N-Oct yl-3,6-d ib r om o-2,7-d im et h oxy-1,8-d im et h ylca r -
ba zole (16). A 1 L flame-dried flask was charged under an
argon atmosphere with 17.0 g (26.0 mmol) of N-octyl-1,3,6,8-
tetrabromo-2,7-dimethoxycarbazole (15),17 520 mL of diethyl
ether, and 104 mL of freshly distilled THF. The stirring
mixture was cooled to -78 °C, and 21.3 mL (53.2 mmol) of
n-butyllithium (2.5 M in hexane) was added dropwise to the
solution over 15 min. The resulting mixture was stirred for 2
h at this temperature, and then 3.31 mL (53.2 mmol) of
iodomethane was added dropwise. The solution was allowed
to warm to room temperature and stirred for 2 h. The resulting
mixture was quenched with distilled water (200 mL) and
extracted with diethyl ether (3 × 100 mL). The combined
organic fractions were dried over magnesium sulfate, and the
solvent was removed under reduced pressure. The residue was
purified by column chromatography (silica gel, 7% ethyl
acetate in hexane as eluent) to afford 8.70 g of the title
1
compound as white crystals (64% yield): mp 120-121 °C; H
NMR (400 MHz, acetone-d6) δ 8.17 (2s, 2H), 4.66 (t, 2H, J )
5710 J . Org. Chem., Vol. 69, No. 17, 2004

Synthesis of Diindolocarbazoles by Cadogan Reaction
7.7 Hz), 3.82 (s, 6H), 2.72 (2s, 6H), 1.49 (m, 2H), 1.18 (m, 10H),
0.82 (t, 3 H, J ) 7.1 Hz); 13C NMR (100 MHz, acetone-d6) δ
154.0, 142.6, 122.1, 121.7, 117.3, 109.6, 60.7, 46.5, 31.8, 30.6,
29.3, 29.2, 26.2, 22.7, 13.8, 12.4; HRMS m/z calculated for
poured in 10 mL of distilled water. The aqueous layer was
extracted with CHCl3 (3 × 30 mL). The combined organic
layers were dried over magnesium sulfate, and the solvent was
removed under reduced pressure. The crude compound was
purified by column chromatography (silica gel, 7% diethyl
ether in hexane as eluent) to provide 640 mg of the title
product as white crystals (69% yield): mp 168-170 °C; 1H
NMR (400 MHz, CDCl3) δ 7.86 (d, 2H, J ) 7.6 Hz), 7.65 (d,
2H, J ) 7.8 Hz), 4.57 (t, 2H, J ) 7.9 Hz), 2.94 (s, 6H), 1.40 (s,
24H), 1.16 (m, 12H), 0.84 (t, 3H, J ) 7.1 Hz); 13C NMR (100
MHz, CDCl3) δ 143.5, 129.3, 128.1, 127.7, 117.2, 83.5, 47.3,
31.7, 29.2, 29.1, 29.1, 26.5, 24.9, 22.6, 19.2, 14.0 (the missing
peak is due to the carbon linked to the boronic function, which
C
24H31NO2Br2 523.0721, found 523.0715.
N-Octyl-2,7-dim eth oxy-1,8-dim eth ylcar bazole (17). This
compound was synthesized according to a similar procedure
to that one used for compound 16 using 10.8 g (20.5 mmol) of
16, 205 mL of diethyl ether, 41 mL of THF, and 16.8 mL (42.1
mmol) of n-butyllithium (2.5 M in hexane). The resulting
mixture was stirred for 1 h at -78 °C, and then 50 mL of
distilled water was added (extraction with chloroform). Crys-
tallization from methanol afforded 6.25 g of the title compound
as a pale yellow solid or a more pure compound could be
obtained by column chromatography (silica gel, 7% ethyl
acetate in hexane as eluent) (83% yield): mp 53-54 °C; 1H
NMR (400 MHz, DMSO-d6) δ 7.74 (d, 2H, J ) 8.4 Hz), 6.87 (d,
2H, J ) 8.4 Hz), 4.42 (t, 2H, J ) 7.4 Hz), 3.82 (s, 6H), 2.47 (s,
shows no signal in 13C NMR); HRMS m/z calculated for C34H51
-
NO4B2 559.4004, found 559.3996.
N -Oct yl-2,7-b is(2′-n it r op h e n yl)-1,8-d im e t h ylca r b a -
zole (21). This compound was synthesized according to a
similar procedure to that one used for compound 4 using 365
mg (0.65 mmol) of 20, 290 mg (1.44 mmol) of 1-bromo-2-
nitrobenzene, 6 mL of toluene, 4.2 mL of K2CO3 2 M, 12 mg
(0.05 mmol) of Pd(OAc)2, and 53 mg (0.20 mmol) of PPh3. The
crude product was purified by column chromatography (silica
gel, 30% diethyl ether in hexane as eluent) to give 260 mg of
the title product as yellow solid (73% yield): mp 157-158 °C;
1H NMR (400 MHz, CDCl3) δ 8.00 (m, 2H), 7.90 (m, 2H), 8.65
(m, 2H), 7.54 (m, 2H), 7.45 (m, 2H), 7.03 (m, 2H), 4.58 (t, 2H,
J ) 8.42), 2.47 (s, 3H), 2.46 (s, 3H), 1.44 (m, 2H), 1.20 (m,
8H), 1.05 (m, 2H), 0.83 (t, 3H, J ) 6.9 Hz); 13C NMR (100 MHz,
CDCl3) δ 149.8, 149.6, 143.0, 143.0, 137.3, 137.3, 136.3, 136.3,
132.8, 132.7, 132.24, 132.23, 128.11, 128.10, 125.61, 125.60,
124.0, 123.9, 121.5, 121.4, 120.2, 120.0, 117.5, 117.46, 47.3 (2s),
31.6 (2s), 29.8 (2s), 29.1 (2s), 29.0 (2s), 26.4 (2s), 22.6 (2s), 17.3
(2s), 17.2 (2s), 14.0 (2s); HRMS m/z calculated for C34H35N3O4
549.2627, found 549.2638.
5,8-Dih ydr o-13,15-dim eth yl-14-octyl-diin dolo[3,2-b:2′,3′-
h ]ca r ba zole (22). A 10 mL flame-dried flask, equipped with
a condenser, was charged with 115 mg (0.21 mmol) of 21 and
4 mL of triethylposphite. The stirred resulting mixture was
heated under reflux under an argon atmosphere for 24 h. The
precipitate formed was collected by filtration, washed with
hexane, and then purified by column chromatography (silica
gel, 30% ethyl acetate in hexane as eluent) to provide 30 mg
of the title product as a yellow solid. (yield ) 30%): mp 280
°C dec; 1H NMR (400 MHz, THF-d8) δ 10.12 (s, 2H, NH), 8.26
(d, 2H, J ) 7.8 Hz), 7.85 (s, 2H), 7.40 (d, 2H, J ) 7.8 Hz), 7.31
(td, 2H, J ) 7.6 and 1.0 Hz), 7.12 (td, 2H, J ) 7.5 and 1.0 Hz),
4.49 (t, 2H, J ) 7.5 Hz), 3.18 (s, 6H), 1.02 (m, 10H), 0.89 (m,
2H), 0.69 (t, 3H, J ) 7.0 Hz); 13C NMR (100 MHz, THF-d8) δ
142.9, 142.8, 138.2, 129.3, 125.6, 125.5, 123.6, 123.5, 119.0,
118.4, 111.1, 99.9, 51.8, 32.9, 30.3, 28.0, 27.5, 26.1, 23.6, 17.5,
14.6; HRMS m/z calculated for C34H35N3 485.2831, found
485.2816.
6H), 1.26 (m, 2H), 1.06 (m, 10H), 0.77 (t, 3H, J ) 7.1 Hz); 13
C
NMR (100 MHz, DMSO-d6) δ 156.3, 143.8, 120.1, 117.5, 109.5,
105.6, 57.0, 46.9, 31.7, 29.8, 29.1, 29.1, 26.2, 22.6, 14.5, 11.9;
HRMS m/z calculated for C24H33NO2 367.2511, found 367.2502.
N-Octyl-2,7-d ih yd r oxy-1,8-d im eth ylca r ba zole (18). This
compound was synthesized according to a similar procedure
to that described previously for the synthesis of compound 12
using 6.0 g (16.3 mmol) of 17, 183 mL of freshly distilled
dichloromethane, and 81.6 mL (81.6 mmol) of boron tribromide
(1 M in dichloromethane). After stirring at -78 °C for 3 h and
at room temperature for 12 h, the mixture was quenched
slowly with approximately 200 mL of HCl 10% (v/v). Crystal-
lization from toluene/hexane afforded 5.45 g of the title
compound as a slightly green solid (98% yield): mp 189-192
°C; 1H NMR (400 MHz, acetone-d6) δ 8.05 (s, 2H), 7.51 (d, 2H,
J ) 8.2 Hz), 6.74 (d, 2H, J ) 8.2 Hz), 4.54 (t, 2H, J ) 7.6 Hz),
2.54 (s, 6H), 1.37 (m, 2H), 1.20 (m, 10H), 0.81 (t, 3H, J ) 7.1
Hz); 13C NMR (100 MHz, acetone-d6) δ 153.5, 143.6, 119.4,
116.4, 109.0, 107.5, 46.7, 31.7, 29.8, 29.3, 29.2, 26.3, 22.6, 13.7,
11.2; HRMS m/z calculated for C22H29NO2 339.2198, found
339.2183.
N-Octyl-2,7-bis(tr iflu or om eth a n esu lfon yl)-1,8-d im eth -
ylca r ba zole (19). This compound was synthesized according
to a similar procedure to that one used for compound 13 using
5.00 g (14.73 mmol) of 18, 1.80 g (14.73 mmol) of 4-(dimethyl-
amino)pyridine, 45 mL of anhydrous pyridine, and 7.43 mL
(44.19 mmol) of trifluoromethanesulfonic anhydride. The crude
compound was purified by column chromatography (silica gel,
10% ethyl acetate in hexane as eluent) to provide 5.20 g of
the title product as a pale yellow solid 59% yield: mp 70-72
°C; 1H NMR (400 MHz, CDCl3) δ 7.89 (d, 2H, J ) 8.5 Hz),
7.19 (d, 2H, J ) 8.5 Hz), 4.62 (t, 2H, J ) 7.9 Hz), 2.75 (s, 6H),
1.51 (m, 2H), 1.17 (m, 10H), 0.84 (t, 3H, J ) 7.1 Hz); 13C NMR
(100 MHz, CDCl3) δ 147.3, 142.6, 123.8, 118.9, 118.6, 115.6,
114.3, 47.0, 31.5, 30.6, 29.0, 29.0, 26.2, 22.5, 14.0, 13.0; HRMS
m/z calculated for C24H27NO6F6S2 603.1184, found 603.1195.
N-Octyl-2,7-bis(4,4,5,5-tetr a m eth yl-1,3,2-d ioxa bor ola n -
2-yl)-1,8-d im eth ylca r ba zole (20). A 25 mL flame-dried two-
necked flask equipped with a condenser was charged succes-
sively with 1.00 g (1.66 mmol) of 19, 6.6 mL of freshly distilled
1,2-dichloroethane, 73 mg (0.10 mmol) of PdCl2(dppf), 1.39 mL
(9.94 mmol) of freshly distilled triethylamine, and 1.44 mL
(9.94 mmol) of 4,4,5,5-tetramethyl-1,3,2-dioxaborolane. The
mixture was stirred under nitrogen at 80 °C for 5 h and then
Ack n ow led gm en t. This work was supported by the
Canada Research Chair program and NSERC grants.
Su p p or tin g In for m a tion Ava ila ble: General experimen-
tal procedures and 1H and 13C NMR spectra for all new
compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
J O049419O
J . Org. Chem, Vol. 69, No. 17, 2004 5711