Synthesis and isolation of iodocarbazoles. Direct iodination reaction 933 of N-substituted carbazoles

Article abstract of DOI:10.1002/jhet.5570390513

Iododerivatives of N-methylcarbazole (1), N-phenylcarbazole (2), N-benzylcarbazole (3), 2-methoxy-N-methylcarbazole (4) and 3-acetamido-N-ethylcarbazole (5) are synthesised. N-Iodosuccinimide (NIS) in tetrahydrofurane/H₂SO₄ (catalyst

Full text of DOI:10.1002/jhet.5570390513

Sep-Oct 2002
Synthesis and Isolation of Iodocarbazoles. Direct Iodination Reaction
of N-Substituted Carbazoles
933
María E. Monge, Sergio M. Bonesi and Rosa Erra-Balsells*
Departamento de Química Orgánica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires,
cc74 - suc30, 1430-Buenos Aires, Argentina
Received December 6, 2001
Iododerivatives of N-methylcarbazole (1), N-phenylcarbazole (2), N-benzylcarbazole (3), 2-methoxy-N-
methylcarbazole (4) and 3-acetamido-N-ethylcarbazole (5) are synthesised. N-Iodosuccinimide (NIS) in
tetrahydrofurane/H SO4 (catalyst), a mixture of KIO3 - KI - H2SO4 (catalyst) in ethanol and a mixture of KIO3
2
- KI in glacial AcOH as iodinating agents have been used and their uses have been compared. The preparation,
isolation and characterization of compounds 1a, 1b, 1c, 1d, 2a, 2b, 3a, 3b, 4a, 4b, 4c and 5a are reported (mp,
tR, Rf, 1H-nmr, 13C-nmr, IR and ms). All of them are described for the first time except 3,6-diiodo-N-phenyl-
carbazole (2b). Semiempirical PM3 calculations have been performed to predict reactivity of N-substituted car-
bazoles and their iododerivatives. Theoretical and experimental results are discussed briefly.
J. Heterocyclic Chem., 39, 933(2002).
Introduction.
In our previous publication [1] we described the synthe-
sis of five iododerivatives of carbazole and several new
iodo derivatives of 2-hydroxy-, 2-acetoxy-, 3-bromo- and
3-nitrocarbazole. As we are interested in the study of pho-
tophysic and photochemistry of azacarbazoles [2-8], car-
bazoles [9,10], N-acetylcarbazole and N-benzoylcarbazole
[11-13] and especially in the photoinduced electron trans-
fer processes in which they can be involved, we decided to
start the study of the photophysical properties of the iodo-
derivatives of the N-substituted carbazoles. Thus, in the
present work we report the synthesis, isolation and charac-
terization of several N-substituted iodocarbazoles prepared
by direct iodination of N-methyl (1), N-phenyl (2), N-ben-
zyl (3), 2-methoxy-N-methyl (4) and 3-acetamido-N-ethyl-
carbazole (5) (Scheme 1: compounds 1a, 1b, 1c, 1d, 2a,
2b, 3a, 3b, 4a, 4b, 4c and 5a).
1 R: Me
2 R: Ph
R
R
R
3
1
2
1a
1b
1c
1d
2a
2b
3a
3b
I
H
I
H
H
H
H
H
H
H
H
I
I
H
I
I
H
I
I
I
3 R: CH Ph
I
I
H
I
2
4
R
R
R
3
1
2
According to our knowledge, polymers containing car-
bazolyl moieties are good electron donors and possess out-
standing electrical and photoelectrical properties [14 - 16].
It is also known that the presence of halogen in the poly-
mer structure modifies their physical properties [17], and
in particular, the presence of iodine in the polymer can
modify the photophysical, and as a consequence, the pho-
toelectrical properties of the polymer owing to the so
called "heavy atom effect" [18].
4a
4b
4c
I
H
H
H
I
I
H
H
I
In contrast to chlorination or bromination, the iodina-
tion of aromatic compounds is a mild reaction and gener-
ally requires some activating catalyst. Traditionally, the
direct iodination reaction of aromatic compounds (ben-
zenic, polynuclear benzenic rings and heterocycles) [19]
5
R
5a
I
system at 50º. Also, heavy metal ions such as Cu(II),
Pb(IV), Sb(V), Co(III), Mn(IV) and Ce(IV) are used as
oxidizing agents combined with alkaline iodide salts in
the presence of 90% trifluoroacetic acid [19]. These iodi-
nating methods are less commonly used because aromatic
compounds with acid labile or oxidizeable substituted
groups (ester, amides, acyloxy, amines and alkyl) are eas-
ily hydrolyzed, protonated and/or oxidized under the
above mentioned experimental conditions.
were carried out with a mixture of KIO or NaIO and
3
4
molecular iodine in ethanol in the presence of catalytic
amounts of sulfuric acid or in glacial acetic acid, which is
used as acid catalyst and solvent, at 70-100°. Other iodi-
nating methods are peracetic acid, hydrogen peroxide
(H O ) and potassium permanganate (KMnO ) as oxidiz-
2
2
4
ing agents to oxidize the molecular iodine in trifluo-
roacetic acid at room temperature or by warming the

934
M. E. Monge, S. M. Bonesi and R. Erra-Balsells
Vol. 39
Recently, we described N-iodosuccinimide (NIS) in
imide in tetrahydrofurane in the presence of catalytic
amount of H SO were used.
dichloromethane [1] as a convenient and mild iodinating
agent providing mono, di and polyiodo compounds
depending on the stoichiometry used.
2
4
N-Methylcarbazole (1) was treated according to the gen-
eral procedure described in Experimental with one to two
equivalents of KIO /KI/H SO (catalytic amount) in
The previously described iodination reaction of N-
3
2
4
ethanol at 55° in order to prepare the iodocarbazole deriv-
atives (Scheme I: 1a, 1b, 1c and 1d). The yields of the
products were determined by gc after an appropriate time
and the results are presented in Table I.
methylcarbazole with one equivalent of KIO /KI in the
3
presence of acetic acid provided a mixture of 3-iodo-N-
methylcarbazole (1b) and 3,6-diiodo-N-methylcarbazole
(1d) which were characterized by their melting point and
elemental analysis [20]. The same authors also described
the preparation of compounds 1b and 1d by the action of
methyl sulfate and potassium hydroxide on 3-iodocar-
bazoles and 3,6-diiodocarbazole, respectively [21].
As it is shown in Table I (entry 1), this reaction provides
a mixture of 3-iodo-N-methylcarbazole (1b) and 3,6-
diiodo-N-methylcarbazole (1d) when one equivalent of
the iodinating reagent was used. Also, in this reaction
mixture 1,6-diiodo-N-methylcarbazole (1c) was detected
as the minor product. We also performed the iodination
reaction of compound 1 at lower temperature (room tem-
perature) but selectivity on the product chemical yields
was not observed. In this case, the reaction time became
longer and the conversion of 1 was not improved (see
Table I, entry 2). When two equivalents of iodinating
agent were used (1:2 molar ratio), 3,6-diiodo-N-methyl-
carbazole (1d) was obtained as the main product and also
compounds 1b and 1c were formed in significant amounts
(see Table I, entry 3).
In our hands, the iodination reaction of N-methylcar-
bazole (1) provides a product distribution that is quite dif-
ferent from that previously reported [20]. The author only
describes the formation of 3-iodo-N-methylcarbazole (1b)
and 3,6-diiodo-N-methylcarbazole (1d) in the reaction
mixture and these compounds were characterized by their
melting point and elemental analysis.
3,6-Diiodo-N-phenylcarbazole (2b) was prepared by
reacting N-phenylcarbazole (2) with two equivalents of a
mixture of KIO /KI in the presence of acetic acid under
3
reflux and it was characterized by its melting point, ele-
mental analysis and ir spectra [22]. Although, Ambrose et
al. [22] pointed out that the purity and the structure of 3,6-
1
diiodo-N-phenylcarbazole (2b) was confirmed by H-nmr
spectroscopy the spectroscopical data were not reported.
As far as we know, the direct iodination of N-benzylcar-
bazole (3), 2-methoxy-N-methyl (4) and 3-acetamido-N-
ethylcarbazole (5) has not been described. Furthermore,
several iododerivatives of these carbazoles and those from
carbazoles 1 and 2 have not been previously described.
In the present paper, we describe the preparation, isola-
tion and characterization of several iodocarbazole deriva-
tives obtained from N-substituted carbazoles (compounds
1, 2, 3, 4 and 5; see Scheme 1) by direct iodination using
two different iodinating agents: i) KIO /KI in the presence
3
The iodination reaction of 1 was also carried out with a
of acid as catalyst and ii) NIS/THF/H SO (cat.). These
2
4
mixture of KIO /KI in glacial acetic acid at 55° (see Table
iodinating systems are convenient as mild reagents for the
selective preparation of mono- and diiodo-N-substituted
carbazoles providing for the first time iodocarbazoles 1a,
1c, 2a, 3a, 3b, 4a, 4b, 4c and 5a (see Scheme 1).
3
I, entries 4 and 5). As it is shown, the production of 1b was
fairly clean when one equivalent of the iodinating agent
was used. The yield of compound 1d was fairly improved
by using two equivalents of the iodinated agent and higher
conversion of the starting material was reached. Besides,
in both reaction mixtures, compounds 1a and 1c were
detected. It is noteworthy to mention that when acetic acid
is used, both as solvent and acid catalyst, monoiodination
reaction preferably occurs using one or two equivalents of
the reagent. Thus, compound 1b is formed as the main
product in both reaction mixtures.
In our previous publication [1] we described the use of
N-iodosuccinimide (NIS) in dichloromethane, as a mild
iodinating agent in the iodination reaction of carbazoles in
neutral conditions. Taking into account these results, we
decided to study the use of NIS for the iodination of N-sub-
stituted carbazoles. Thus, N-methylcarbazole (1) in
We also describe the use of several chromatographic
methods (tlc, gc and column chromatography) in order to
(i) follow the iodination reaction, (ii) determine the yields
of the reactions and (iii) isolate for complete characteriza-
1
13
tion (elemental analysis, R , t , mp, UV, H-nmr, C-nmr
f
R
and ms) of the iododerivatives obtained.
Additionally, computational chemistry has been used to
calculate the atomic charge density values. Those for the
more relevant atoms are collected in Tables VI and they
are used to discuss the reactivity of carbazoles 1-5.
Results and Discussion.
In order to investigate the iodination reaction of N-sub-
stituted carbazoles 1-5, we decided to carry out the reac-
tion systematically and comparatively by using different
CH Cl with N-iodosuccinimide (1:1 molar ratio) was
2
2
iodinating reagents. Thus, KIO /KI in ethanol with cat-
alytic amounts of concentrated sulfuric acid, or in glacial
acetic acid as solvent-catalyst [20 - 22], and N-iodosuccin-
treated in the absence of light, at room temperature, during
2 hours. The gc analysis of the reaction mixture showed
that 3-iodo-N-methylcarbazole (1b) was formed as the
3

Sep-Oct 2002
Synthesis and Isolation of Iodocarbazoles
935
only product in 12% yield (see Table I, entry 8). Besides,
no improvement on the chemical yield of 1b was observed
when the reaction was left to stand for additional 7 hours.
However, when the iodination reaction of N-methylcar-
bazole (1) was carried out with one equivalent of NIS in
duced the expected products, 3-iodo-N-phenyl (2a) and
3-iodo-N-benzylcarbazole (3a) respectively, in good yield
(see Table II, entry 1 and Table III, entry 1). However, in
both reaction mixtures significant amounts of the corre-
sponding 3,6-diodo-N-phenyl (2b) and 3,6-diiodo-N-ben-
Table I
Iodination of N-Methylcarbazole (1) by using Different Methods
Products (% Yield) [a]
Experiment
Method [b]
Carbazole:IA
(molar ratio) [c]
Conversion
(%)
1a
1b
1c
1d
1
2 [d]
(i)
(i)
(i)
(ii)
(ii)
(iii)
(iii)
(iv)
1:1
1:1
1:2
1:1
1:2
1:1
1:2
1:1
94
95
-
-
-
3.7
0.6
-
83.1
84.0
3.4
78.2
59.4
76.7
18.4
12
2.0
2.1
1.5
2.4
2.4
1.4
1.9
-
8.8
7.5
95.1
10.3
35.2
8.7
3
4
5
6
7
8
100
94.5
97.6
86.9
100
12
-
-
79.7
-
[a] Quantitative gc (ZB-5) analysis. Reaction time: 120 minutes; [b] Method: (i) KIO /KI/EtOH/H SO (catalyst), T: 55°; (ii) KIO /KI/AcOH, T: 55°;
3
2
4
3
(iii) N-Iodosuccinimide (NIS)/THF/H SO (catalyst), T: 40°, (iv) N-Iodosuccinimide (NIS)/CH Cl , T: 25°; [c] N-Methylcarbazole to iodinating agent
2
4
2
2
(IA) molar ratio; [d] Experiment at room temperature.
Table II
Iodination of N-Phenylcarbazole (2) by using Different Methods
Products (% Yield) [a]
Experiment
Method [b]
Carbazole:IA
(molar ratio) [c]
Conversion
(%)
2a
2b
1
2
3
4
5
6
(i)
(i)
(ii)
(ii)
(iii)
(iii)
1:1
1:2
1:1
1:2
1:1
1:2
88.3
100
88.5
100
80.5
99
80.3
0.8
81.2
68.8
78.5
46
7.9
99.2
7.3
31.0
2
53
[a] Quantitative gc (ZB-5) analysis. Reaction time: 300 minutes; [b] Method: (i) KIO /KI/EtOH/H SO (catalyst), T: 55°; (ii) KIO /KI/AcOH, T: 55°;
3
2
4
3
(iii) N-Iodosuccinimide (NIS)/THF/H SO (catalyst), T: 40°; [c] N-Phenylcarbazole to iodinating agent (IA) molar ratio.
2
4
Table III
tetrahydrofurane in the presence of catalytic amount of
H SO at 40°, the product distribution changed dramati-
Iodination of N-Benzylcarbazole (3) by using Different Methods
Products (% Yield) [a]
2
4
cally and the chemical yields were improved (see Table I,
entry 6). This reaction provides 3-iodo-N-methylcarbazole
(1b) as the main product (76.7%) together with 1,6-diiodo-
N-methylcarbazole (1c, 1.4%) and 3,6-diiodo-N-methyl-
carbazole (1d, 8.7%). When the iodination reaction of 1
was carried out with two equivalents of N-iodosuccin-
imide, production of 3,6-diiodo-N-methylcarabzole (1d)
was higher (79.7%) but a significant amount of 1b was
also obtained. Compound 1c was also detected in the reac-
tion mixture (see Table I, entry 7).
Experiment Method Carbazole:IA
Conversion
(%)
3a
3b
[b]
(molar ratio) [c]
1
2
3
4
5
6
(i)
(i)
(ii)
(ii)
(iii)
(iii)
1:1
1:2
1:1
1:2
1:1
1:2
100
100
77.7
83.0
82.7
99.5
75.9
29.7
74.4
78.9
79.1
15.9
23.3
70.3
3.3
4.1
3.6
83.6
[a] Quantitative gc (ZB-5) analysis. Reaction time: 120 minutes; [b]
Method: (i) KIO /KI/EtOH/H SO (catalyst), T: 55°; (ii)
3
2
4
KIO /KI/AcOH, T: 55°; (iii) N-Iodosuccinimide (NIS)/THF/H SO (cat-
3
2
4
N-Phenylcarbazole (2) and N-benzylcarbazole (3) are
rather less reactive than N-methylcarbazole. Thus, the iod-
alyst), T: 40°; [c] N-Benzylcarbazole to iodinating agent (IA) molar ratio.
ination reactions with a mixture of KIO /KI/H SO in
3
2
4
ethanol (1:1 molar ratio) were carried out at 55° during
longer periods of time. Monoiodination of 2 and 3 pro-
zylcarbazole (3b) were obtained. When two equivalents of
the iodinating agent were used, the expected 3,6-diiodo-N-

936
M. E. Monge, S. M. Bonesi and R. Erra-Balsells
Vol. 39
phenylcarbazole (2b) was obtained in a high yield (99.2 %;
see Table II, entry 2) while 3,6-diiodo-N-benzylcarbazole
(3b) was formed in good yield (see Table III, entry 2) but a
significant amount of compound 3a was also detected in
the reaction mixture. In all these iodinating reactions, a
high conversion of the starting material was reached.
The iodination reactions of 2 and 3 were also carried out
while, in the iodination reaction of N-phenyl and N-ben-
zylcarbazole, neither 1-iodo nor 1,6-diiodo-N-substituted
carbazoles were detected in the reaction mixtures.
Comparing these results with those obtained when the iod-
ination reaction of carbazole was performed with a mix-
ture of NaIO /I /H SO in ethanol [1], we conclude that
4
2
2
4
+
the incoming electrophile (I ) at the ortho-position of the
carbazole moiety is dramatically diminished when a sub-
stituent group is attached to the heteroatom. This behavior
is due to the presence of a bulky N-substituent such as
methyl, phenyl and benzyl group in the carbazole moiety
and, at the same time, to the high molecular volume of the
with a mixture of KIO /KI in glacial acetic acid at 55°and
3
the results are shown in Table II, entry 3 and Table III,
entry 3, respectively. As it is shown, the production of 2a
and 3a was fairly clean. As it has been discussed previ-
ously, monoiodination is the preferential reaction using
both one and two equivalents of this reagent (see Table II,
entry 4 and Table III, entry 4).
We also studied the iodination reaction of N-phenylcar-
bazole (2) and N-benzylcarbazole (3) with one and two
equivalents of N-iodosuccinimide in THF doped with cat-
alytic amount of sulfuric acid at 40° in the absence of light
(see Tables II and III, entries 5 and 6, respectively). Thus,
the production of 3-iodo-N-phenylcarbazole (2a) was
fairly clean when one equivalent of NIS was used and 3,6-
diiodo-N-phenylcarbazole (2b) was also detected in the
reaction mixture. The same pattern of results was obtained
with N-benzylcarbazole (3) in these conditions. When two
equivalents of NIS were used, compounds 2a and 2b were
formed in almost 1:1 molar ratio.
+
electrophile (I ). Therefore, a steric effect at the ortho-
position of the carbazole moiety is operating in the elec-
trophilic iodination reaction of N-substituted carbazole
derivatives.
We also studied the iodination reaction of 2-methoxy-N-
methylcarbazole (4) according to the general procedure
described in the Experimental. The yields of the products
obtained (gc) are presented in Table IV. As it is shown in
this table (entry 1) the reaction conducted at 55º provided
3-iodo-2-methoxy-N-methylcarbazole (4b), together with
significant amounts of 3,6-diiodo-2-methoxy-N-methyl-
carbazole (4c) and traces of 1-iodo-2-methoxy-N-methyl-
carbazole (4a) when one equivalent of iodinating agent
+
(KIO /KI/H ) was used. When two equivalents of the iod-
3
When N-benzylcarbazole (3) reacted with N-iodosuccin-
imide in a molar ratio 1:1 at 40°, again 3-iodo-N-benzylcar-
bazole (3a) was obtained as the main product together with
a 3.6% yield of 3,6-diiodo-N-benzylcarbazole (3b) whereas
the iodination reaction of 3 with two equivalents of NIS
rends 3b in 83.6% yield together with significant amount of
compound 3a (see Table III, entries 5 and 6). Comparing
entries 2 and 6 in Table II, we conclude that compound 2b
is obtained in high yield (99.2%) when the iodinating mix-
inating agent were used, 3,6-diiodo-2-methoxy-N-methyl-
carbazole (4c) was formed in a fairly good yield together
with traces of 4a and 4b (see Table IV, entry 2) and a total
consumption of the starting material was reached.
Simultaneously, we carried out the iodination reaction of
4 with KIO /KI in glacial acetic acid and the results are
3
shown in Table IV (entries 3 and 4). Again, one equivalent
of the iodinating agent provides a mixture of compounds
4b and 4c in almost a 9:1 molar ratio, while when two
equivalents of the iodinating agent were used, similar
product yields were obtained.
ture KIO /KI/EtOH/H SO (catalyst) is used.
3
2
4
It is noteworthy to mention that in the iodination reac-
tion of N-methylcarbazole, 1-iodo-N-methyl (1a) and 1,6-
diiodo-N-methylcarbazole (1c) were formed in low yield
The iodination reactions of 2-methoxy-N-methylcar-
bazole (4) with one and two equivalents of N-iodosuccin-
Table IV
Iodination of 2-Methoxy-N-methylcarbazole (4) by using Different Methods
Products (% Yield) [a]
Experiment
Method [b]
Carbazole:IA
Conversion
4a
4b
4c
(molar ratio) [c]
(%)
1
2
3
4
5
6
(i)
(i)
(ii)
(ii)
(iii)
(iii)
1:1
1:2
1:1
1:2
1:1
1:2
99.8
100
99.1
99.1
82.0
99.4
0.9
1.2
0.8
0.9
6.8
1.1
69.0
0.6
88.0
81.1
75.2
28.8
29.9
98.0
10.4
17.1
-
69.5
[a] Quantitative gc (ZB-5) analysis. Reaction time: 120 minutes; [b] Method: (i) KIO /KI/EtOH/H SO (catalyst), T: 55°; (ii) KIO / KI / AcOH,
3
2
4
3
T: 55°; (iii)N-Iodosuccinimide (NIS)/THF/H SO (catalyst), T: 40°; [c] 2-Methoxy-N-methylcarbazole to iodinating agent (IA) molar ratio.
2
4

Sep-Oct 2002
Synthesis and Isolation of Iodocarbazoles
937
imide were also studied. As it is shown in Table IV
(entries 5 and 6), the use of one equivalent of NIS as iodi-
nating agent provides 3-iodo-2-methoxy-N-methylcar-
bazole (4b) in 75.2% yield together with 1-iodo-2-
methoxy-N-methylcarbazole (4a). Any diiodo derivative
(4c) was detected in the reaction mixture. When two
equivalents of NIS were used, 3,6-diiodo-2-methoxy-N-
methylcarbazole (4c) was formed in good yield together
with significant amount of compound 4b. Compound 4a
was also detected in the reaction mixture.
primary products which in turn give 1,6-diiodo-N-methyl-
carbazole (1c) and 3,6-diiodo-N-methylcarbazole (1d),
respectively, where 1d is the main product of the iodina-
tion reaction of 1 (see Table I, entries 1 and 3). Following
the kinetic profiles obtained for the iodination reaction of
the N-substituted carbazoles (2 – 5), all of the mono and
diiodo-N-substituted carbazoles are formed in parallel
reactions.
The differential reactivity of the carbazoles 1 – 5
towards the electrophilic substitution iodination could be
rationalized taking into account charge distribution. As it
is known the static charge distribution is frequently used
for interpreting and predicting chemical reactivity and it
should indicate favorable sites for kinetic attack by incom-
ing reagents. The net atomic charge values were calculated
by using the semi empirical PM3 method as implemented
in the version of the HyperChem 5.1 program [23] to
obtain the optimized geometry of the N-substituted car-
bazoles and their iodo derivatives.
The iodination reaction of 3-acetamido-N-ethylcar-
bazole (5) with one equivalent of KIO /KI/H SO in
3
2
4
ethanol yielded 6-iodo-3-acetamido-N-ethylcarbazole (5a)
as the sole product in 90.6% yield. When two equivalents
of the iodinating agent were used, again the only product
detected in the reaction mixture was 5a in 100% yield (see
Table V, entries 1 and 2). When the acid catalyst used in
the iodination reaction of 5 was glacial acetic acid instead
of sulfuric acid, similar results were obtained. Thus, the
use of one or two equivalents of the iodinating agent
The static atomic charge density values calculated for
compounds 1, 2, 3, 4 and 5 and their iododerivatives are
collected in Table VI. These N-substituted carbazoles (1 –
5) have the highest negative values localized at C-1, C-3,
C-6 and C-8 and it would be expected that the incoming
(KIO /KI) in acetic acid gives as sole product 5a in very
3
high yield and the conversion of starting material is almost
complete (see Table V, entries 3 and 4).
Finally, we studied the iodination reaction of 3-
acetmido-N-ethylcarbazole (5) with one and two equiva-
lents of N-iodosuccinimide and the results are shown in
Table V (entries 5 and 6). As it is shown, 6-iodo-3-
acetamido-N-ethylcarbazole (5a) was formed again as the
sole product in 100% yield when one or two equivalents
were used.
Furthermore, as it was pointed out above, all these reac-
tions were monitored by gc in order to obtain additional
information about the mechanism of the iodination reac-
tion. The kinetic profiles obtained for the iodination reac-
tion of 1 with one equivalent of the reagent, show that 1a
and 1b are formed in parallel reactions. When two equiva-
lents of the iodinating agent are used, 1a and 1b are the
+
iodine cation (I ) could preferentially attack these posi-
tions. It is worthwhile to point out that C-3 and C-6 have
the highest negative charge density values compared to
that of C-1 and C-8.
As it is shown in Table VI, the static charge values pat-
tern of carbazoles 1 and 4 show the preferential elec-
trophilic substitution positions, which are in agreement
with the experimental results obtained. Besides, for car-
bazoles 2, 3 and 5, even though the highest negative charge
density values are localized at C-1, C-3 and also at C-6, C-
8, the experimental results obtained show a preferential
para-substitution mechanism. These results can be
explained taking into account the large volume of the
+
iodine cation (I ) and the bulky group (phenyl, benzyl and
ethyl) attached to the nitrogen atom of the carbazole moi-
ety. Both effects operate simultaneously and make the
approach of the electrophile (I ) difficult at the orto-posi-
Table V
Iodination of 3-Acetamido-N-ethylcarbazole (5) by using Different Methods
+
Products (% Yield) [a]
tion (1-C and 8-C) of the carbazole moiety. The difference
Experiment
Method [b]
Carbazole:IA
(molar ratio) [c]
Conversion
(%)
5a
in the DH calculated for each pair of iodo derivatives iso-
f
mers (1-, 3-iododerivatives of carbazole and mono- and
diiododerivatives obtained from compounds 1-5, see Table
VI) agree with the regioselectivity observed.
1
2
3
4
5
6
(i)
(i)
(ii)
(ii)
(iii)
(iii)
1:1
1:2
1:1
1:2
1:1
1:2
90.6
100
98.8
100
100
100
90.6
100
98.8
100
100
100
EXPERIMENTAL
Thin layer chromatography (tlc) analysis was performed with
aluminum silica gel sheets (0.2 layer thickness, silica-gel 60
F254). Gas chromatography (gc) analysis was conducted with a
Zebron ZB-5 column (Crosslinked 5% Phenylpolysiloxane; 30m
x 0.25mm x 0.50 mm; Capillary column). Mass spectra (ms)
[a] Quantitative gc (ZB-5) analysis. Reaction time: 120 minutes;
[b] Method: (i) KIO /KI/EtOH/H SO (catalyst), T: 55°; (ii) KIO /KI/
3
2
4
3
AcOH, T: 55°; (iii) N-Iodosuccinimide (NIS)/ THF / H SO (catalyst), T:
2
4
40°; [c] 3-Acetamido-N-ethylcarbazole to iodinating agent (IA) molar ratio.

938
M. E. Monge, S. M. Bonesi and R. Erra-Balsells
Vol. 39
Table VI
Static Charge Distribution for N-Methylcarbazole (1), N-Phenylcarbazole (2), N-Benzylcarbazole (3), 2-Methoxy-N-methylcarbazole (4) and
3-Acetamido-N-ethylcarbazole (5) and DH for the Iododerivatives [a]
f
Atom Number
Compounds
1-C
2-C
3-C
4-C
5-C
6-C
7-C
8-C
DH [b]
f
1
-0.131
-0.126
-0.120
-0.128
-0.118
-0.177
-0.113
-0.112
-0.113
-0.114
-0.113
-0.212
-0.212
-0.214
-0.195
-0.099
-0.098
-0.073
-0.072
-0.054
-0.069
-0.052
-0.085
-0.044
-0.062
-0.081
-0.060
-0.057
0.119
0.148
0.142
0.137
-0.084
-0.082
-0.140
-0.119
-0.159
-0.118
-0.162
-0.126
-0.153
-0.155
-0.129
-0.153
-0.154
-0.174
-0.182
-0.212
-0.207
-0.110
-0.108
-0.040
-0.052
-0.017
-0.049
-0.015
-0.048
-0.024
-0.022
-0.048
-0.024
-0.021
-0.007
-0.006
0.017
1a
1b
1c
1d
2
2a
2b
3
3a
3b
4
4a
4b
4c
5
-0.049
-0.039
-0.026
-0.015
-0.124
-0.135
-0.150
-0.159
-0.082
-0.073
-0.060
-0.052
-0.104
-0.120
-0.100
-0.116
81.26569
74.73787
102.51580
97.57286
-0.046
-0.124
-0.083
-0.116
109.89489[c]
131.43211[d]
-0.045
-0.022
-0.047
-0.046
-0.046
-0.031
-0.046
-0.022
-0.128
-0.153
-0.134
-0.130
-0.131
-0.147
-0.126
-0.155
-0.078
-0.057
-0.080
-0.081
-0.080
-0.065
-0.078
-0.056
-0.112
-0.108
-0.120
-0.113
-0.117
-0.100
-0.110
-0.107
100.71176[e]
121.92529[f]
47.82892
40.04039
61.23724[g]
0.011
-0.073
-0.070
5a
22.63604[h]
[a] Calculations were performed using PM3 method [23]; [b] DH in kcal/mol; DH for 1-iodocarbazole: 79.72475 kcal/mol and for 3-iodocarbazole:
f
f
75.83298 kcal/mol; [c] DH for 1-iodo-N-phenylcarbazole: 115.05375 kcal/mol; [d] DH for 1,6-diiodo-N-phenylcarbazole: 159.19018 kcal/mol;
f
f
[e] DH for 1-iodo-N-benzylcarbazole: 109.94786 kcal/mol; [f] DH for 1,6-diiodo-N-benzylcarbazole: 131.17812 kcal/mol; [g] DH for 1,6-diiodo-2-
f
f
f
methoxy-N-ethylcarbazole: 75.22029 kcal/mol and for 1,3-diiodo-2-methoxy-N-ethylcarbazole: 80.99334 kcal/mol; [h] DH for 1-iodo-3(N-acetyl-
f
amine)-N-ethylcarbazole: 31.03466 kcal/mol.
were obtained under electron impact (70 eV). The ratios m/z and
the relative intensities are reported. Products were isolated by
preparative thick layer chromatography (PLC Merck Plates,
20x20 cm, silica gel 60 F254, 2 mm thickness) and column chro-
matography (Aldrich silica gel 200-400 mesh 60Å). Pure hexane
and hexane-ethyl acetate mixtures were used as eluent. Melting
under normal (air) atmosphere. The reaction mixture was neutral-
ized with sodium bisulphite, extracted with dichloromethane (3 x
15 mL) and washed with water (3 x 20 mL). The combined
organic extracts were dried over anhydrous sodium sulfate, fil-
tered and evaporated in vacuo to give a brownish solid residue.
The residue was separated by column chromatography (silica gel-
hexane-ethyl acetate mixtures) to give (1a), (1b), (1c) and (1d).
According to the experimental conditions used the percentage
yield of the products obtained are different as can be seen in Table
I (see Results and Discussion). Besides, these set of reaction were
performed in glacial acetic acid instead of ethanol, because it
works as solvent and acid catalyst simultaneously.
1
13
points are uncorrected. H- and C-nmr spectra were run in
deuterochloroform at 200 MHz. Chemical shifts are reported in
13
ppm values, using tetramethylsilane as internal standard. C-
nmr assignments were confirmed by using DEPT pulse sequence.
Dichloromethane, tetrahydrofurane, benzene, acetic acid,
ethanol, hexane, ethyl acetate and other reagents used were ana-
lytical grade. Solvents were freshly distilled and dried before
using. Carbazole, N-methylcarbazole, N-phenylcarbazole,
3-amino-N-ethylcarbazole and N-iodosuccinimide were pur-
chased from Aldrich. 2-Hydroxycarbazole was purchased from
Aldrich and was recrystallized from ethanol before use.
2-Methoxy-N-methylcarbazole [24], N-benzylcarbazole [25] and
3-acetamido-N-ethylcarbazole [26] were prepared according to
the procedure described in the literature.
1-Iodo-N-methylcarbazole (1a).
This compound was obtained as white needles (hexane), mp
95-96 °; 1H-nmr (deuterochloroform): d 8.05 (d, 1 H, 5-H, J = 7.8
Hz), 7.90 (dd, 1 H, 4-H, J = 1.8 and 8.0 Hz), 7.45 (dd, 1 H, 2-H,
J = 1.8 and 8.0 Hz), 7.43-7.38 (m, 2 H, 6- and 7-H), 7.25 (dd, 8-
H, J = 2.0 and 7.8 Hz), 7.15 (dd, 1 H, 3-H, J = 8.0 and 8.0 Hz),
3.80 ppm (s, 3 H, CH3); ms: m/z 307 (26), 306 (M+., 100), 179
(19), 178 (24), 166 (25), 139 ( 15).
General Procedure for the Iodination Reaction of N-Methyl-
carbazole (1) with KIO3 /KI/Catalytic Acid Systems.
Anal. Calcd. for C13H10NI: C, 50.84; H, 3.28; N, 4.56; I,
41.32. Found: C, 50.80; H, 3.30; N, 4.54; I, 41.28.
To a stirred solution of N-methylcarbazole (1) (100 mg, 0.55
mmoles) in ethanol (20 mL) solid sodium iodate (0.15 to 0.30
mmole depending on the stoichiometry used) and potassium
iodine previousley grinned (0.28 to 0.56 mmole depending on the
stoichiometry used) were added. Then concentrated sulfuric acid
(42 mL to 1.68 mL depending on the stoichiometry used, d: 1.85
g/mL) was added drop wise. The reaction was stirred for an appro-
priate time in the absence of light at 55° until the tlc and gc indi-
cated that it was completed. All of these reactions were carried out
3-Iodo-N-methylcarbazole (1b).
This compound was obtained as white needles (hexane), mp 67-
69°; 1H-nmr (deuterochloroform): d 8.40 (d, 1 H, 4-H, J = 1.9 Hz),
8.04 (d, 1H, 5-H, J = 7.8 Hz), 7.72 (dd, 1 H, 2-H, J = 1.9 and 8.5
Hz), 7.52 (dd, 1 H, 7-H, J = 7.8 and 7.8 Hz), 7.39 (dd, 1 H, 8-H, J =
2.3 and 7.8 Hz), 7.27 (ddd, 1 H, 6-H, J = 2.3, 7.8 and 7.8 Hz), 7.17
(d, 1 H, 1-H, J = 8.5 Hz), 3.82 ppm (s, 3 H, CH3); 13C-nmr
(deuterochloroform): d 140.9, 140.0, 133.8, 129.0, 126.5, 125.3,

Sep-Oct 2002
Synthesis and Isolation of Iodocarbazoles
939
121.5, 120.6, 119.4, 110.6, 108.7, 81.5, 29.0 ppm; ms: m/z 307
(15), 306 (M+., 100), 179 (19), 178 (35), 166 (42), 139 ( 18).
Anal. Calcd. for C13H10NI: C, 50.84; H, 3.28; N, 4.56; I,
41.32. Found: C, 51.00; H, 3.25; N, 4.52; I, 41.28.
Anal. Calcd. for C18H11NI2: C, 43.67; H, 2.24; N, 2.83; I,
51.26. Found: C, 43.65; H, 2.27; N, 2.80; I, 51.22.
Iodination Reaction of N-Benzylcarbazole (3) with N-Iodo-
succinimide.
1,6-Diiodo-N-methylcarbazole (1c).
The iodination reaction of N-benzylcarbazole (3) was per-
formed according to the general procedure described above. The
brownish solid residue was separated by preparative thin layer
chromatography (silica gel; hexane-benzene (90:10)) to give two
crystalline products 3a and 3b. The percentage yields of the prod-
ucts obtained are presented in Table III (see Result and
Discussion).
This compound was obtained as white needles (hexane), mp
120-121°; 1H-nmr (deuterochloroform): d 8.00 (d, 1 H, 5 - H, J =
2.0 Hz), 7.95 (d, 1 H, 4 - H, J = 8.0 Hz), 7.45 (d, 1 H, 2 - H, J =
8.0 Hz), 7.30 (d, 1 H, 8 - H, J = 7.8 Hz), 7.25 (dd, 1 H, 7 - H, J =
2.0 and 7.8 Hz), 7.10 (dd, 1 H, 3 - H, J = 8.0 and 8.0 Hz), 3.79
ppm (s, 3 H, CH3); ms: m/z 434 (13), 433 (M+.,100), 307 (6), 306
(21), 247 (31), 245 (33), 216 (17), 179 (19), 178 (24), 166 (25),
139 ( 15).
3-Iodo-N-benzylcarbazole (3a).
This compound was obtained as white needles (hexane), mp
107-109°; 1H-nmr (deuterochloroform): d 8.44 (dd, 1 H, 5-H, J =
1.6 and 8.0 Hz), 8.07 (d, 1 H, 4-H, J = 1.9), 7.70 - 7.63 (m, 2 H,
2- and 7-H), 7.53 (m, 2 H, 10- and 14-H), 7.32-7.24 (m, 3 H, 11-,
12- and 13-H), 7.31 (dd, 1 H, 6-H, J = 8.0 and 8.0 Hz), 7.18 (d, 1
H, 8-H, J = 8.8 Hz), 7.15 (d, 1 H, 1-H, J = 8.4 Hz), 5.50 ppm (s, 2
H, CH2); 13C-nmr (deuterochloroform): d 140.7, 139.9, 136.8,
134.1, 129.5, 129.3, 127.7, 126.6, 126.4, 125.6, 121.9, 120.6,
119.8,111.1, 109.2, 81.9, 46.5 ppm; ms: m/z 384 ( 5), 383 (M+.,
22), 292 (1), 257 (8), 167 (16), 164 (5), 91 (100).
Anal. Calcd. for C13H9NI2: C, 36.06; H, 2.09; N, 3.23; I,
58.61. Found: C, 36.10; H, 2.01; N, 3.24; I, 58.31.
3,6-Diiodo-N-methylcarbazole (1d).
This compound was obtained as white needles (hexane), mp
1
187°; H-nmr (deuterochloroform): d 8.32 (d, 2 H, 4- and 5-H,
J = 1.6 Hz), 7.72 (dd, 2H, 2- and 7-H, J = 1.6 and 7.0 Hz), 7.16 (d,
2 H, 1- and 8-H, J = 7.0 Hz), 3.79 ppm (s, 3 H, CH3); 13C-nmr
(deuterochloroform): d 140.1, 134.6, 129.3, 123.9, 110.7, 81.8,
29.3 ppm; ms: m/z 434 (10), 433 (M+., 100), 307 (6), 306 (21),
179 (29), 178 (34), 166 (55), 139 ( 15).
Anal. Calcd. for C19H14NI: C, 59.55; H, 3.68; N, 3.65; I,
33.11. Found: C, 59.53; H, 3.64; N, 3.67; I, 33.10.
Anal. Calcd. for C13H9NI2: C, 36.06; H, 2.09; N, 3.23; I,
58.61. Found: C, 36.00; H, 2.11; N, 3.21; I, 58.34.
3,6-Diiodo-N-benzylcarbazole (3b).
Iodination Reaction of N-Phenylcarbazole (2) with KIO3/KI/
Catalytic Acid Systems.
This compound was obtained as white needles (hexane), mp
169-172°; H-nmr (deuterochloroform): d 8.38 (d, 2 H, 4- and
1
5-H, J = 1.5 Hz), 7.70 (dd, 2 H, 2- and 7-H, J = 1.5 and 8.8 Hz),
7.55 (m, 2 H, 10- and 14-H), 7.28-7.23 (m, 3 H, 11-, 12- and 13-
H), 7.15 ppm (d, 2 H, 1- and 8-H, J = 8.8 Hz); 13C-nmr (deute-
rochloroform): d 139.3, 137.1, 134.3, 129.3, 128.3, 127.3, 126.5,
123.5, 112.1, 82.5, 45.6 ppm; ms: m/z 509 (M+., 1), 384 (5), 383
(26), 292 (2), 254 (4), 166 (2), 164 (7), 91 (100).
The iodination reaction of N-phenylcarbazole (2) was per-
formed according to the general procedure described above. The
brownish solid residue was separated by preparative thick layer
chromatography (silica gel; hexane-benzene (90:10)) to give two
crystalline products 2a and 2b. The percentage yields of the prod-
ucts obtained are presented in Table II (see Result and
Discussion).
Anal. Calcd. for C19H13NI2: C, 44.82; H, 2.57; N, 2.75; I,
49.85. Found: C, 44.80; H, 2.50; N, 2.78; I, 49.82.
3-Iodo-N-phenylcarbazole (2a).
Iodination Reaction of 2-Methoxy-N-methylcarbazole (4) with
KIO3/KI/Catalytic Acid Systems.
This compound was obtained as white needles (hexane), mp
107-109°; 1H-nmr (deuterochloroform): d 8.43 (dd, 1 H, 5-H, J =
1.6 and 8.0 Hz), 8.09 (d, 1 H, 4-H, J = 2.0 Hz), 7.70 - 7.63 (m, 2
H, 2- and 7-H), 7.53 (m, 2 H, 10- and 14-H), 7.41-7.38 (m, 3 H,
11-, 12- and 13-H), 7.31 (dd, 1 H, 6-H, J = 8.0 and 8.0 Hz), 7.18
(d, 1 H, 8-H, J = 8.8 Hz), 7.15 ppm (d, 1 H, 1-H, J = 8.4 Hz); 13C-
nmr (deuterochloroform): d 141.1, 140.2, 137.4, 134.3, 130.2,
129.3, 127.9, 127.1, 126.8, 126.0, 124.5, 120.6, 120.5,111.9,
110.0, 82.3 ppm; ms: m/z 369 (26), 368 (M+., 100), 242 (10), 241
(7), 239 (15), 165 (3), 164 (13), 138 (4).
The iodination reaction of 2-methoxy-N-methylcarbazole (4)
was performed according to the general procedure described
above. The brownish solid residue was separated by column
chromatography (silica gel-hexane-ethyl acetate mixtures) to
give three crystalline products 4a, 4b and 4c. The percentage
yields of the products obtained are presented in Table IV (see
Result and Discussion).
1-Iodo-2-methoxy-N-methylcarbazole (4a).
Anal. Calcd. for C18H12NI: C, 58.56; H, 3.28; N, 3.79; I,
34.37. Found: C, 58.50; H, 3.30; N, 3.80; I, 34.35.
This compound was obtained as white needles (hexane), mp
130°; 1H-nmr (deuterochloroform): d 7.99 (dd, 1 H, 5-H, J = 2.3
and 7.8 Hz), 7.87 (d, 1 H, 4-H, J = 8.4 Hz ), 7.38 (m, 2 H, 6- and
7-H), 7.19 (d, 1 H, 8-H, J = 7.0 Hz), 6.89 (d, 1 H, 3-H, J = 8.4
Hz), 4.09 (s, 3 H, CH3N), 3.95 ppm (s, 3 H, CH3O); 13C-nmr
(deuterochloroform): d 159.2, 150.1, 139.6, 125.7, 124.6, 119.4,
119.1, 119.0, 117.8, 108.4, 104.7, 79.1, 56.7, 29.2 ppm; ms: m/z
338 (10), 337 (M+., 100), 322 (20), 294 (13), 208 (3), 196 (5),
195 (39), 180 (26), 167 (34), 152 (27), 139 (10).
3,6-Diiodo-N-phenylcarbazole (2b).
This compound was obtained as white needles (hexane), mp
179-180° ([22] 179-182°); 1H-nmr (deuterochloroform): d 8.40
(d, 2 H, 4- and 5-H, J = 1.5 Hz), 7.67 (dd, 2 H, 2- and 7-H, J = 1.5
and 8.8 Hz ), 7.60 (m, 2 H, 10- and 14-H), 7.55-7.45 (m, 3 H, 11-,
12- and 13-H), 7.15 ppm (d, 2 H, 1- and 8-H, J = 8.8 Hz); 13C-nmr
(deuterochloroform): d 140.1, 136.8, 135.0, 130.2, 129.4, 128.2,
127.0, 124.5, 112.0, 83.1 ppm; ms: m/z 496 ( 23), 495 (M+., 100),
368 (27), 242 (10), 241 (7), 239 (15), 164 (13), 138 (4).
Anal. Calcd. for C14H12NOI: C, 49.87; H, 3.59; N, 4.15; I,
37.64. Found: C, 49.85; H, 3.60; N, 4.12; I, 37.65.

940
M. E. Monge, S. M. Bonesi and R. Erra-Balsells
Vol. 39
3-Iodo-2-methoxy-N-methylcarbazole (4b).
catalytic acid systems. The product yields obtained in different
experimental conditions are shown in Table I, entries 6 and 7 (see
Results and Discussion).
This compound was obtained as white needles (hexane), mp
160-163°; 1H-nmr (deuterochloroform): d 8.43 (s, 1 H, 4-H),
7.95 (d, 1 H, 5-H, J = 7.7 Hz), 7.43-7.38 (m, 2 H, 6- and 7-H),
7.23 (dd, 1 H, 8-H, J = 2.0 and 7.6 Hz), 6.83 (s, 1 H, 1-H), 4.01 (s,
1 H, CH3O), 3.81 ppm (s, 1 H, CH3N); 13C-nmr (deuterochloro-
form): d 156.5, 142.3, 141.0, 130.6, 125.0, 121.7, 119.6, 119.5,
118.8, 108.4, 91.5, 75.2, 56.6, 29.1 ppm; ms: m/z 338 (15), 337
(M+., 100), 322 (21), 294 (19), 208 (3), 196 (6), 195 (42), 180
(26), 167 (30), 152 (24), 139 ( 12).
Iodination Reaction of Carbazoles 2 - 5 with N-Iodosuccinimide.
The iodination reaction of carbazoles 2 – 5 with N-iodosuccin-
imide was performed according to the general procedure
described above. The percentage yields of the products obtained
are shown in Tables II, III, IV and V (entries 5 and 6), respec-
tively (see Results and Discussion).
Anal. Calcd. for C14H12NOI: C, 49.87; H, 3.59; N, 4.15; I,
37.64. Found: C, 49.82; H, 3.57; N, 4.12; I, 37.66.
Iodination Reaction of N-Methylcarbazole (1) with N-Iodo-
succinimide in Dichloromethane.
3,6-Diiodo-2-methoxy-N-methylcarbazole (4c).
To a stirred solution of N-methylcarbazole (1) (100 mg, 0.55
mmole) in dichloromethane (10 mL) solid N-iodosuccinimide
(0.55 mmole) was added. The reaction was stirred for an appro-
priate time in the absence of light at room temperature until the
tlc and gc indicated that it was completed. This reaction was car-
ried out under normal (air) atmosphere. The reaction mixture was
evaporated in vacuo to give a brownish solid residue. The residue
was separated by column chromatography (silica gel-hexane-
ethyl acetate mixtures) to give (1b) and recovered starting mater-
ial (1). The percentage yield of the product obtained is shown in
Table I, entry 8 (see Results and Discussion).
This compound was obtained as white needles (hexane), mp
198°; 1H-nmr (deuterochloroform): d 8.33 (s, 1 H, 4-H), 8.20 (d,
1 H, 5-H, J = 1.1 Hz), 7.62 (dd, 1 H, 7-H, J = 1.1 and 8.8 Hz),
7.09 (d, 1 H, 8-H, J = 8.8 Hz), 6.74 (s, 1 H, 1-H), 3.99 (s, 1 H,
CH3O), 3.74 ppm (s, 1 H, CH3N); 13C-nmr (deuterochloroform):
d 153.1, 141.8, 139.4, 134.4, 130.9, 128.4, 124.1, 117.0, 110.4,
91.3, 82.0, 75.2, 56.7, 29.2 ppm; ms: m/z 464 (12), 463 (M+.,
100), 338 (15), 322 (23), 294 (15), 208 (8), 196 (6), 195 (52), 180
(26), 167 (34), 152 (24), 139 ( 12).
Anal. Calcd. for C14H11NOI2: C, 36.31; H, 2.39; N, 3.02; I,
54.81. Found: C, 36.30; H, 2.35; N, 3.04; I, 54.79.
Calculations.
Iodination Reaction of 3-Acetamido-N-ethylcarbazole (5) with
KIO3/KI/Catalytic Acid Systems.
The ground-state geometry and heat of formation, static charge
distribution for predicting chemical reactivity of carbazoles 1 - 5
and iodocarbazoles were calculated by using the semiempirical
parametrized PM3 method as implemented in version of the
HyperChem program [23]. This method has proven to be effec-
tive in studies on molecules containing heteroatoms, compared
with other methods such as MINDO/3 or MNDO.
The iodination reaction of 3-acetamido-N-methylcarbazole (5)
was performed according to the general procedure described
above. The yellowish solid residue was separated by column
chromatography (silica gel-hexane-ethyl acetate mixtures) to
give a crystalline product 5a. The percentage yield of the product
obtained is presented in Table V (see Result and Discussion).
Acknowledgment.
3-Acetamido-6-iodo-N-ethylcarbazole (5a).
Partial financial support from UBA and CONICET is grate-
fully acknowledged. Authors are also grateful to Dr. H. Nonami
(College of Agriculture, Ehime University, Japan) for
HyperChem Suite for professionals release 5.1 program and Dr.
M. A. Ponce for nmr spectra. S. M. Bonesi and R. Erra-Balsells
are research members of CONICET.
This compound was obtained as white needles (hexane), mp
1
175°; H-nmr (deuterochloroform): d 8.32 (d, 1 H, 5-H, J = 1.5
Hz), 8.18 (d, 1 H, 4-H, J = 1.5 Hz), 7.66 (dd, 1 H, 2-H, J = 1.5
and 8.8 Hz), 7.54 (dd, 1 H, 7-H, J = 1.5 and 8.8 Hz), 7.31 (d, 1 H,
1-H, J = 8.8 Hz), 7.16 (d, 1 H, 8-H, J = 8.8 Hz), 4.28 (q, 2 H,
CH2), 2.19 (s, 3 H, CH3CONH), 1.36 ppm (t, 3 H, CH3); 13C-nmr
(deuterochloroform): d 169.7, 139.4, 137.0, 133.8, 130.4, 129.2,
125.2, 121.5, 120.3, 112.8, 110.5, 108.5, 80.7, 37.5, 23.4, 13.4
ppm; ms: m/z 370 (19), 369 (M+., 100), 243 (6), 242 (30), 241
(45), 240 (14), 213 (3), 164 (6), 121 (7), 51 (20).
REFERENCES AND NOTES
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Anal. Calcd. for C16H15N2OI: C, 50.81; H, 4.00; N, 7.41; I,
33.55. Found: C, 50.79; H, 3.99; N, 7.43; I, 33.52.
General Procedure for the Iodination Reaction of N-Methyl-
carbazole (1) with N-Iodosuccinimide in Tetrahydrofurane.
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To a stirred solution of N-methylcarbazole (1) (100 mg, 0.55
mmole) in tetrahydrofurane (10 mL) solid N-iodosuccinimide
(0.55 mmole to 1.10 mmoles depending on the stoichiometry
used) was added. Then, concentrated sulfuric acid (42 ml; d: 1.85
g/mL) was carefully added. The reaction was stirred for an appro-
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out under normal (air) atmosphere. After the reaction mixture
was neutralized with sodium hydroxide, the work-up was similar
to that previously described for the reaction with KIO3/KI/
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4
Photobehaviour of b- Carbolines, unpublished results.
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Synthesis and Isolation of Iodocarbazoles
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