Superelectrophilic iodination of deactivated arenes with triiodoisocyanuric acid

Article abstract of DOI:10.1055/s-0030-1258429

The reaction of triiodoisocyanuric acid (TICA) with deactivated arenes in acidic medium led to the efficient and regioselective formation of the corresponding iodoarenes, in 55-88% isolated yield. The acidity of the medium was found to be the most important factor influencing the electrophilic iodination of weakly nucleophilic substrates by TICA. Georg Thieme Verlag Stuttgart New York.

Full text of DOI:10.1055/s-0030-1258429

PAPER
739
Superelectrophilic Iodination of Deactivated Arenes with Triiodoisocyanuric
Acid
Iodination of
D
ea
o
ctivated
A
re
d
nes rigo S. da Ribeiro, Pierre M. Esteves,* Marcio C. S. de Mattos*
Instituto de Química, Departamento de Química Orgânica, Universidade Federal do Rio de Janeiro, Cx. Postal 68545, 21945-970,
Rio de Janeiro, Brazil
Fax +55(21)25627256; E-mail: mmattos@iq.ufrj.br; E-mail: pesteves@iq.ufrj.br
Received 9 November 2010; revised 15 December 2010
compounds have been extensively used in radioimmu-
Abstract: The reaction of triiodoisocyanuric acid (TICA) with de-
noassay studies and in nuclear magnetic imaging.4
activated arenes in acidic medium led to the efficient and regiose-
lective formation of the corresponding iodoarenes, in 55–88%
isolated yield. The acidity of the medium was found to be the most
important factor influencing the electrophilic iodination of weakly
nucleophilic substrates by TICA.
Aryl iodides are usually more difficult to prepare than the
corresponding aryl chlorides and bromides due to the low
electrophilicity of iodine which requires the presence of
an activating agent in order to produce a strongly electro-
philic ‘I+’ species. Direct iodination is also hampered by
the formation of hydrogen iodide, which is both a strong
reducing agent and a strong acid that can cause protolytic
cleavage of sensitive compounds.5
Key words: triiodoisocyanuric acid, iodination, deactivated aro-
matic compound, iodoarene, electrophilic halogenation
Several important compounds that exhibit biological ac-
tivity, e.g. thyroid hormones (like thyroxine), dakaramine,
and fialuridine, have a C–I bond in their structure
(Figure 1).
A large number of synthetic methods are available for the
iodination of activated arenes, but there are only a limited
number of methods for the direct iodination of deactivated
aromatics.6 Some arenes with electron-withdrawing sub-
stituents can be iodinated by I2/HNO3/H2SO4/AcOH,7a I2/
SbCl5,7a I2/Ag2SO4/H2SO4,7b I2/oleum,7c ICl/Ag2SO4/
H2SO4,7d I2/AgOTf,7e and IPy2BF4/TfOH,7f and PyICl,7g I2
or KI/NaIO4/H2SO4,7h I2/IBX,7i and I2/K2S2O8 in strong
acid.7j,k However, some of these reactions involve corro-
sive reagents, the use of heavy metal oxidants, or the for-
mation of byproducts that are sometimes difficult to
separate. Potent iodination agents such as N-iodosuccin-
imide in triflic acid,8a and 2,4,6,8-tetraiodoglycoluril in
sulfuric acid8b are capable of iodinating strongly deacti-
vated arenes, but the former is limited on a large prepara-
tive scale by the expense of triflic acid, while the second
affords iodoarenes in generally moderate yields when us-
ing two equivalents of the ‘active iodine’.
I
OH
O
I
NMe2
I
I
I
Me2N
O
dakaramine
I
I
O
O
N
NH
HO
CO2H
O
NH2
thyroxine
HO
F
fialuridine
Figure 1 Organoiodo compounds with biological activity
Triiodoisocyanuric acid (TICA, Figure 2), was recently
reported by us as an efficient reagent for the co-iodination
of alkenes with oxygenated nucleophiles,9 and the iodina-
tion of activated arenes.10 In addition, TICA has the ad-
vantage of transferring three equivalents of iodine atom to
the substrate, that is of up to 75% of its mass. As an exten-
sion of our search for more potent and practical electro-
philic halogenation reagents,11 in the present work we
describe our results on the iodination of deactivated aro-
matic rings using triiodoisocyanuric acid in acidic medi-
um, as the source of superelectrophilic iodine.12
Iodoarenes are also compounds of high practical utility as
precursors of a variety of active pharmaceutical ingredi-
ents, such as camptothecin,1a dehydrotubifoline,1b mor-
phine,1c sangliferine A,1d ecteinascidine 743,1e etc.
Furthermore, iodoarenes have been extensively used in ar-
omatic bond formation reactions such as Heck arylation2a
and Stille,2b Negishi,2c Suzuki,2d Buchwald,2e and
Sonogashira2f couplings. In some of these reactions, even
with another halide present on the aromatic ring, the cou-
pling occurs selectively at the iodo group.3 Another im-
portant application of organoiodo compounds is in
radiopharmaceuticals. Radioactively labeled iodoarene
I
O
I
N
O
I
TICA
N
N
SYNTHESIS 2011, No. 5, pp 0739–0744
Advanced online publication: 10.02.2011
x
x
.
x
x
.2
0
1
1
O
DOI: 10.1055/s-0030-1258429; Art ID: M07510SS
© Georg Thieme Verlag Stuttgart · New York
Figure 2

740
R. S. da Ribeiro et al.
PAPER
The iodination of chlorobenzene with TICA in acetoni- ring the arene with 0.34 molar equivalents of TICA at dif-
trile was not observed after 72 hours at room temperature. ferent temperatures and acid strengths. Weakly
However changing the solvent to 98% sulfuric acid led to deactivated arenes (entries 1–4) were smoothly monoiod-
the formation of several polyiodinated products, while us- inated using sulfuric acid diluted in acetic acid at room
ing sulfuric acid diluted with acetic acid gave a cleaner re- temperature, while more deactivated arenes needed higher
action; the monoiodinated products were obtained using sulfuric acid concentrations. On the other hand, highly de-
H2SO4–AcOH 1:8 (Scheme 1).
activated arenes (entries 11–13) were iodinated by TICA
in 65% oleum (65% SO3 in H2SO4) at higher tempera-
tures. Unfortunately, 1,3,5-trinitrobenzene was unreactive
under these conditions.
Based on the above results, we studied the reaction of de-
activated arenes with TICA in acidic media with the aim
of forming the monoiodinated products and the results are
shown in Table 1. The reactions were performed by stir- The products were characterized by their melting points
and/or spectrometric techniques. The regioselectivity of
MeCN
the reactions was very high and no regioisomers were de-
no reaction
tected by the analytical procedures employed (HRGC, 1H
r.t.
and 13C NMR spectroscopy). However, exceptions were
I
observed in the reactions of chloro-, bromo-, and iodoben-
O
I
N
O
I
zene which produced both o- and p-iodo-substituted ha-
loarenes in which the p-regioisomers predominated
(entries 2–4). In these cases, the identities of the products
were determined by NMR spectra which were in good
agreement with those previously reported.7j,13 Curiously,
the reaction of methyl benzoate with TICA in 98% sulfu-
ric acid (entry 9) produced the expected m-iodinated ester
(63%) along with benzoic acid (33%). The unexpected
formation of the carboxylic acid without incorporating io-
dine can be explained by a partial reaction of the ester with
sulfuric acid to produce the benzoyl cation, which is too
deactivated to be iodinated by TICA in 98% sulfuric acid.
Further treatment with water during the workup process
leads to benzoic acid, as shown in Scheme 2.
H2SO4
r.t.
mixture of polyiodinated
chlorobenzenes
Cl
N
N
O
Cl
H2SO4–AcOH
(2:3)
(n = 1–3)
In
H2SO4–AcOH
(1:8)
Cl
+
Cl
I
r.t., 13 h
81%
I
(4:1)
Scheme 1
CO2Me
As observed in the reactions of deactivated arenes with
trichloroisocyanuric14 and tribromoisocyanuric15 acids in
acidic media, we believe that sulfuric acid promotes O-
protonation of TICA forming a polyprotonated or proto-
solvated superelectrophilic species16 (Scheme 3). This
species can act as an efficient iodenium-transfer agent due
to the intramolecular charge–charge repulsion and it is
possible to regulate the reactivity of the reagent by modu-
lation of the acid strength of the media. The increase of the
degree of protonation of the TICA can lead to higher reac-
tivity of such species, since the reactant is destabilized by
the charge–charge repulsion in relation to the transition
I
O
N
O
I
CO2Me
N
N
I
I
(63%)
CO
O
98% H2SO4
CO2H
H2O
(workup)
(33%)
Scheme 2
I
I
I
I
HO
I
N
O
I
HO
I
N
OH
I
HO
I
N
OH
I
O
I
N
O
I
H
H
H
N
N
N
N
N
N
N
N
O
O
OH
O
I
I
I
HO
I
N
O
I
HO
I
N
OH
I
HO
I
N
OH
I
N
N
N
N
N
N
O
O
OH
Scheme 3
Synthesis 2011, No. 5, 739–744 © Thieme Stuttgart · New York

PAPER
Iodination of Deactivated Arenes
741
state for I+ release, decreasing the activation barrier. reactive powerful electrophile obtained by the system
Hence, iodination of phenyl halides was observed in less TICA/oleum was able to attack even relatively unreactive
acidic conditions whereas polyiodination was more prom- strongly deactivated arene nucleophiles (1,3-dinitroben-
inent in more acidic media. Not surprisingly, the highly zene, 2,6-dinitrotoluene).
Table 1 Iodination of Deactivated Arenes
I
O
I
N
O
I
conditions
ArH
+
ArI
N
N
O
(0.34 equiv)
Entry
1
Substrate
Product
Conditions
Yield (%)a
83
F
F
H2SO4–AcOH (1:10), r.t., 14 h
I
I
Cl
+
Cl
Cl
Br
I
2
3
4
H2SO4–AcOH (1:8), r.t., 13 h
H2SO4–AcOH (1:8), r.t., 13 h
H2SO4–AcOH (1:8), r.t., 13 h
81b
80b
86b
I
(4 : 1)
Br
Br
+
I
I
I
(3 : 1)
I
+
I
I
I
(2.2 : 1)
CONH2
CO2H
CF3
CONH2
5
6
7
8
9
H2SO4–AcOH (1:1), r.t., 144 h
H2SO4–AcOH (3:2), r.t., 24 h
H2SO4–AcOH (3:2), r.t., 24 h
H2SO4–AcOH (4:1), r.t., 24 h
98% H2SO4, r.t., 2 h
88c
55
I
I
I
I
CO2H
CF3
80
NO2
NO2
78
CO2Me
CO2Me
63d
I
F
F
F
F
F
F
10
98% H2SO4, r.t., 18 h
74
F
F
F
F
O2N
NO2
O2N
NO2
11
12
65% oleum, 70 °C, 17 h
65% oleum, 70 °C, 17 h
80
58
I
NO2
NO2
NO2
I
NO2
Synthesis 2011, No. 5, 739–744 © Thieme Stuttgart · New York

742
R. S. da Ribeiro et al.
PAPER
Table 1 Iodination of Deactivated Arenes (continued)
I
O
I
N
O
I
conditions
ArH
+
ArI
N
N
O
(0.34 equiv)
Entry
13
Substrate
Product
Conditions
Yield (%)a
CO2H
I
CO2H
65% oleum, 70 °C, 19 h
80
–
Cl
Cl
NO2
NO2
O2N
NO2
14
15
–
–
65% oleum, 80 °C, 46 h
65% oleum, 80 °C, 46 h
NO2
CO2H
OH
–
O2N
NO2
a Yield of pure product, based on arene.
b Product ratio determined by HRGC.
c TICA used: 0.68 equiv.
d Formed together with benzoic acid (33%).
1-Fluoro-4-iodobenzene7j
In conclusion, we have shown that the use of acidic medi-
um increases the reactivity of TICA, allowing the iodina-
tion of deactivated aromatic rings. We favor an
explanation in which there is probably participation of the
polyprotonated form of TICA in this process.
1H NMR (CDCl3): d = 6.84 (t, J = 8.9 Hz, 2 H), 7.63 (dd, J = 8.9,
5.1 Hz, 2 H).
13C NMR (CDCl3): d = 87.13 (d, J = 3.5 Hz), 118.0 (d, J = 22.2 Hz),
139.2 (d, J = 7.7 Hz), 160.5 (d, J = 247.3 Hz).
1-Chloro-4-iodobenzene7j
Triiodoisocyanuric acid (TICA) was prepared from trichloroisocy-
anuric acid as previously described.9 1H and 13C NMR spectra were
recorded on a Bruker AC-200 (200 MHz and 50 MHz, respectively)
spectrometer in CDCl3 or DMSO-d6 solutions with TMS as an in-
ternal standard. High-resolution GC was performed on a HP-5890-
II gas chromatograph with FID using a 30 m (length), 0.25 mm
(i.d.), and 25 mm (phase thickness) RTX-5 capillary column and H2
(flow rate 50 cm/s) as carrier gas (split: 1:10). HRGC-MS analyses
were performed on a Shimadzu GCMS-QP2010S gas chromato-
graph with electron impact (70 eV) by using a 30 m DB-5 silica cap-
illary column.
1H NMR (CDCl3): d = 7.07 (d, J = 8.8 Hz, 2 H), 7.60 (d, J = 8.8 Hz,
2 H).
13C NMR (CDCl3): d = 91.2, 130.6, 134.3, 138.8.
1-Chloro-2-iodobenzene13
1H NMR (CDCl3): d = 6.94 (t, J = 7.9 Hz, 1 H), 7.27 (t, J = 7.9 Hz,
1 H), 7.45 (d, J = 7.9 Hz, 1 H), 7.85 (d, J = 7.9 Hz, 1 H).
13C NMR (CDCl3): d = 98.2, 127.9, 129.5, 138.6, 140.3.
1-Bromo-4-iodobenzene7j
1H NMR (CDCl3): d = 7.24 (d, J = 8.5 Hz, 2 H), 7.55 (d, J = 8.5 Hz,
2 H).
Iodination of Deactivated Arenes with TICA; General Proce-
dure
13C NMR (CDCl3): d = 92.2, 122.4, 133.7, 139.3.
To a stirred soln of the arene (2 mmol) in acidic medium (5 mL, ac-
cording to Table 1), was added TICA (0.67 mmol) at r.t. (in the case
of 1,3-dinitrobenzene, 2,6-dinitrotoluene, and 4-chloro-3-nitroben-
zoic acid the reaction was performed at 70 °C) and in the absence of
light. The reaction was monitored by HRGC-MS and after the spec-
ified time (Table 1) the mixture was poured onto crushed ice (100
g). The aqueous layer was washed with EtOAc (3 × 15 mL), cyanu-
ric acid was filtered off, and the combined organic layers were treat-
ed with 10% aq Na2SO3 (50 mL) and carefully neutralized with 10%
Na2CO3 (except carboxylic acids which were washed with concd
NaCl). The organic layer was dried (anhyd Na2SO4) and filtered.
The solvent was evaporated on a rotary evaporator and the product
collected. Selected analytical data follow.
1-Bromo-2-iodobenzene13
13C NMR (CDCl3): d = 101.4, 128.6, 129.6, 133.0, 133.3, 140.5.
1,4-Diiodobenzene7j
1H NMR (CDCl3): d = 7.42 (s, 4 H).
13C NMR (CDCl3): d = 93.5, 139.5.
1,2-Diiodobenzene13
13C NMR (CDCl3): d = 108.0, 129.3, 139.6.
3-Iodobenzamide17
Mp 183–185 °C (Lit.17 185–186 °C).
Synthesis 2011, No. 5, 739–744 © Thieme Stuttgart · New York

PAPER
Iodination of Deactivated Arenes
743
1H NMR (DMSO-d6): d = 7.25 (t, J = 7.9 Hz, 1 H), 7.47 (br s, 1 H),
7.87 (dd, J = 7.9, 1.4 Hz, 2 H), 8.09 (br s, 1 H), 8.20 (t, J = 1.4 Hz,
1 H).
13C NMR (DMSO-d6): d = 94.7, 127.1, 130.7, 136.2, 136.4, 140.1,
166.8.
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Mp 181–183 °C (Lit.7j 185–186 °C).
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13C NMR (DMSO-d6): d = 95.2, 129.2, 131.4, 133.4, 138.2, 141.9,
166.5.
1-Iodo-3-(trifluoromethyl)benzene7j
1H NMR (CDCl3): d = 7.23 (t, J = 7.9 Hz, 1 H), 7.61 (d, J = 7.9 Hz,
1 H), 7.90 (d, J = 7.9 Hz, 1 H), 7.97 (s, 1 H).
13C NMR (CDCl3): d = 93.9 (s), 123.0 (q, J = 273.0 Hz), 124.5 (q,
J = 3.8 Hz), 130.5 (s), 132.5 (q, J = 32.6 Hz), 134.3 (q, J = 3.8 Hz),
141.0 (s).
1-Iodo-3-nitrobenzene18
1H NMR (CDCl3): d = 7.30 (t, J = 8.0 Hz, 1 H), 8.03 (d, J = 8.0 Hz,
1 H), 8.20 (dd, J = 8.0, 2.0 Hz, 1 H), 8.57 (t, J = 2.0 Hz, 1 H).
13C NMR (CDCl3): d = 93.5, 122.8, 130.8, 132.5, 143.5, 148.6.
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Tetrahedron 2004, 60, 9113.
Methyl 3-Iodobenzoate19
Mp 50–52 °C (Lit.19 54.5 °C).
(7) (a) Merkushev, E. B. Synthesis 1988, 923. (b) Baker, I. R.
L.; Waters, W. A. J. Chem. Soc. 1952, 150. (c) Arotsky, J.;
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1H NMR (CDCl3): d = 3.92 (s, 3 H), 7.18 (t, J = 7.9 Hz, 1 H), 7.88
(d, J = 7.9 Hz, 1 H), 8.00 (d, J = 7.9 Hz, 1 H), 8.38 (s, 1 H).
13C NMR (CDCl3): d = 52.5, 93.9, 128.9, 130.2, 132.1, 138.6,
141.9, 165.7.
Pentafluoroiodobenzene20
13C NMR (CDCl3): d = 66.1 (td, J = 28.2, 4.6 Hz), 134.3–140.1 (m),
138.8–144.5 (m), 144.6–149.9 (m).
MS: m/z (%) = 294 (M+, 100), 275, 167, 148, 127, 117.
1-Iodo-3,5-dinitrobenzene21
Mp 100–101 °C (Lit.21 102–103 °C).
1H NMR (CDCl3): d = 8.89 (d, J = 2.0 Hz, 2 H), 9.03 (t, J = 2.0 Hz,
1 H).
13C NMR (CDCl3): d = 93.6, 118.6, 137.9, 148.7.
4-Iodo-2,6-dinitrotoluene22
Mp 87.5–90 °C (Lit.22 87.5–90 °C).
(9) Ribeiro, R. da S..; Esteves, P. M.; de Mattos, M. C. S.
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(10) Ribeiro, R. da S..; Esteves, P. M.; de Mattos, M. C. S.
J. Braz. Chem. Soc. 2008, 19, 1239.
1H NMR (CDCl3): d = 2.51 (s, 3 H), 8.28 (s, 2 H).
13C NMR (CDCl3): d = 14.9, 89.3, 126.9, 136.2, 152.0.
MS: m/z (%) = 308 (M+), 291, 127, 89 (100), 77, 63, 50.
(11) (a) Mendonça, G. F.; Sanseverino, A. M.; de Mattos, M. C.
S. Synthesis 2003, 45. (b) de Souza, S. P. L.; da Silva, J. F.
M.; de Mattos, M. C. S. J. Braz. Chem. Soc. 2003, 14, 832.
(c) Almeida, L. S.; Esteves, P. M.; de Mattos, M. C. S.
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M. C. S.; Esteves, P. M. Synthesis 2010, 2379.
4-Chloro-3-iodo-5-nitrobenzoic Acid
Mp 188–189 °C
1H NMR (CDCl3): d = 8.43 (d, J = 1.9 Hz, 1 H), 8.77 (d, J = 1.9 Hz,
1 H).
13C NMR (DMSO-d6): d = 103.0, 125.2, 131.8, 132.9, 143.0, 148.2,
163.9.
Acknowledgment
(12) Chaikovskii, V. K.; Filimonov, V. D.; Funk, A. A. Russ. J.
Org. Chem. 2009, 45, 1349.
(13) Aldrich Handbook of Fine Chemicals, Aldrich Chemical Co.
(available at http://www.sigmaaldrich.com).
The authors thank CNPq, CAPES, and FAPERJ for financial sup-
port.
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R. S. da Ribeiro et al.
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