Facile synthesis of 2,3-diiodonaphthalene and 2-bromo-3-iodonaphthalene

Article abstract of DOI:10.1081/SCC-120021997

2,3-Diiodonaphthalene (5) and 2-bromo-3-iodonaphthalene (6) were readily synthesized in two steps by iodination of the corresponding bis(hexachlorocyclopentadiene) adducts 1 and 3 of naphthalene and 2-bromonaphthalene, in methanesulfonic acid, followed by retro Diels-Alder reaction combined with sublimation.

Full text of DOI:10.1081/SCC-120021997

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Facile Synthesis of 2,3-Diiodonaphthalene and 2-
Bromo-3-iodonaphthalene
Jonas Hellberg a , Fredrik Allared a & Margit Pelcman a b
a Organic Chemistry , Royal Institute of Technology , Stockholm, Sweden
b Biovitrum AB , SE-112 87 Stockholm, Sweden
Published online: 17 Aug 2006.
To cite this article: Jonas Hellberg , Fredrik Allared & Margit Pelcman (2003) Facile Synthesis of 2,3-Diiodonaphthalene and 2-
Bromo-3-iodonaphthalene, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 33:15, 2751-2756, DOI: 10.1081/SCC-120021997
To link to this article: http://dx.doi.org/10.1081/SCC-120021997
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 15, pp. 2751–2756, 2003
Facile Synthesis of 2,3-Diiodonaphthalene
and 2-Bromo-3-iodonaphthalene
#
*
Jonas Hellberg, Fredrik Allared, and Margit Pelcman
Organic Chemistry, Royal Institute of Technology,
Stockholm, Sweden
ABSTRACT
2,3-Diiodonaphthalene (5) and 2-bromo-3-iodonaphthalene (6) were
readily synthesized in two steps by iodination of the corresponding
bis(hexachlorocyclopentadiene) adducts 1 and 3 of naphthalene and
2-bromonaphthalene, in methanesulfonic acid, followed by retro
Diels-Alder reaction combined with sublimation.
Key Words: 2,3-Diiodonaphthalene; 2-Bromo-3-iodonaphthalene;
Iodination; Retro Diels-Alder.
*Correspondence: Jonas Hellberg, Organic Chemistry, Royal Institute of
Technology, SE-100 44 Stockholm, Sweden; Fax: þ46-8-791 2333; E-mail:
jhel@orgchem.kth.se.
#Current address: Margit Pelcman, Biovitrum AB, SE-112 87 Stockholm,
Sweden.
2751
DOI: 10.1081/SCC-120021997
Copyright & 2003 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
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2752
Hellberg, Allared, and Pelcman
2,3-Diiodonaphthalene (5) and 2-bromo-3-iodonaphthalene (6)
have despite their simplicity rarely been reported in the literature.
2,3-Diiodonaphthalene (5) has been mentioned once without reference
to its synthesis[1] and once in a synthesis from 2,3-diaminonaphthalene
yielding 0.5% of 5.[2] It has also been made by cyclization of 2,3-bis-
(iodoethynyl)benzene.[3] 2-Bromo-3-iodonaphthalene (6) has been synthe-
sized once before, in a multistep synthesis.[4] Since we needed
considerable amounts of 5 in a project directed to annulated dioxins,[5]
and since there should be a interest in these compounds as starting
materials for organometallic ligands and as extended p-systems, we
decided to develop a new practical synthesis. Our synthesis takes advan-
tage of the propensity of naphthalene bis(hexachlorocyclopentadiene)
adduct 1 to undergo electrophilic aromatic substitution in its b-position
rather than the more reactive a-position in unsubstituted
naphthalene. This has previously been used for the synthesis of several
2-substituted and 2,3-disubstituted naphthalenes.[6,7] Whereas the
brominated derivative 3 is commercially available, iodination of 1 has
not been described.
There are numerous methods for iodination of aromatic sub-
strates,[8] and among the more useful is the Suzuki procedure.[9,10]
Although versatile, this method requires strenous conditions, such
as concentrated sulfuric acid as solvent when applied to unactivated
aromatics.[11,12]
Our starting material 1 resisted iodination under both normal Suzuki
conditions and in sulfuric acid. We did however observe that 1 has lim-
ited solubility in sulfuric acid, which may account for its low reactivity.
When performed in methanesulfonic acid, the iodination proceeded
smoothly to give high yield of the diiodo derivative 2 when stirring at
room temperature overnight or until discoloration (Sch. 1).
The retro Diels-Alder reaction was conveniently performed in a gra-
dient sublimation tube, where 2 was heated to 210ꢀC under vacuum
(1.0–1.5 ꢁ 10ꢂ2 mbar). Analytically pure 2,3-diiodonaphthalene (5) was
deposited in a well defined zone in the middle of the tube. Depending on
the scale and type of sublimation tube, yields between 50–83%
were obtained. The same reaction sequence, starting with the com-
mercially available 2-bromonaphthalene-bis(hexachlorocyclopentadiene)
adduct (3) produced the 2-bromo, 3-iodo intermediate 4 in 98% yield,
and the corresponding 2-bromo, 3-iodonaphthalene (6) in 40–83% yield
respectively (Sch. 2).
In conclusion we have developed a practical and convenient method
for the preparation of 2,3-diiodonaphthalene (5) and 2-bromo-3-iodo-
naphthalene (6).

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2,3-Diiodonaphthalene and 2-Bromo-3-iodonaphthalene
2753
Scheme 1.
Scheme 2.
EXPERIMENTAL
The naphthalene-hexachlorocyclopentadiene adducts were pur-
chased from Aldrich. All materials and solvents were used as received.
Nuclear magnetic resonance spectra were recorded on a Bruker
400 MHz or 500 MHz spectrometer. Mass spectra were recorded on a

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2754
Hellberg, Allared, and Pelcman
Finnigan SSQ. Elemental analyses were performed by Analytische
Laboratorien GMBH, Lindlar, Germany.
2,3-Diiodo-bis(hexachlorocyclopentadiene)naphthalene
Adduct, 2
H5IO6, (653 mg, 2.86 mmol) was dissolved in 100 mL methanesul-
fonic acid at room temperature. After 30 min, I2 (2.18 g, 8.58 mmol)
was added. The flask was equipped with a drying tube and the mixture
was allowed to stir for 2 h during which a powerful coloration developed.
Bis(hexachlorocyclopentadiene)naphthalene adduct 1 (6.73 g, 9.99 mmol)
was then added in portions over 5 min, after which the reaction mixture
was allowed to stir at room temperature for two days (until discolora-
tion). The pale yellow solution was then poured onto 400 mL ice/water,
from which the crude product was collected via filtration after 30 min as a
white solid. The material was washed with water and dried, affording 2
(8.43 g, 9.59 mmol, 96%). M.p. 214–217ꢀC (dec.). H-NMR (CDCl3): ꢀ
1
8.17 (s, 2H), 3.84 (d, 2H, J ¼ 8.8 Hz), 3.50 (d, 2H, J ¼ 8.8 Hz). 13C-NMR
(CDCl3): ꢀ 140.03, 133.51, 130.32, 129.63, 107.26, 101.49, 84.78, 82.50,
46.72, 41.88. MS shows predominatly the Mþ peak for the retro Diels-
Alder product 2,3-diiodonaphthalene 5, see below.
2,3-Diiodonaphthalene, 5
The iodinated product 2 (8.21 g, 8.87 mmol) was placed in a gradient
sublimation tube. The sublimator was placed so that the vacuum end
(outlet to pump) was pointing downward from the hot end-zone. The
substance was heated to 210ꢀC, and a vacuum 1.0–1.5 ꢁ 10ꢂ2 mbar was
applied. Hexachlorocyclopentadiene soon started to emerge at the
vacuum side, and the pure 2,3-diiodonaphthalene (5) deposited slowly
higher in the sublimation tube. The starting material also sublimed, form-
ing a band of white crystals well separated from the product. After 1 h,
the sublimation was interrupted, and the formed hexachlorocyclopenta-
diene was poured off, the sublimed starting material was returned to the
end of the tube. The sublimation was resumed, and after 1 h the proce-
dure was repeated once more. After completion of the sublimation/retro
Diels-Alder reaction, 5 (2.80 g, 7.36 mmol, 83%) was collected as off-
white crystals, and some 2 (486 mg, 0.525 mmol, 6%) as white crystals.
M.p. 114.0–114.8ꢀC. 1H-NMR (CDCl3): ꢀ 8.40 (s, 2H), 7.67 (m, 2H), 7.48
(m, 2H). 13C-NMR: ꢀ 138.74, 134.16, 127.57, 127.07, 104.56. MS: 380

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2,3-Diiodonaphthalene and 2-Bromo-3-iodonaphthalene
2755
(Mþ 78%), 253 (M-I, 24%), 126 (M-2I, 100%). Anal. calcd. for C10H6I2:
C 31.61, H 1.59. Found: C 31.82, H 1.54.
2-Bromo-3-iodo-bis(hexachlorocyclopentadiene)napthalene
Adduct, 4
H5IO6, (655 mg, 2.87 mmol) was added to 100 mL methanesulfonic
acid at room temperature. After 30 min, I2 (2.18 g, 8.58 mmol) was
added. The flask was equipped with a drying tube and the mixture
was allowed to stir for 2 h during which a powerful coloration
developed. Bis(hexachlorocyclopentadiene)naphthalene adduct (3,
15.05 g, 20.00 mmol) was then added in portions over 3 min, after
which the reaction mixture was allowed to stir at room temperature for
four days. The colorless solution was then poured onto ice/water, from
which the crude product was collected via filtration after 30 min, as a
white solid. The material was washed with water, dried under vacuum,
affording 4 as a fine white powder (17.27 g, 19.66 mmol, 98% yield). M.p.
199–200ꢀC (dec.). 1H-NMR (CDCl3): ꢀ 8.20 (s, 1H), 7.96 (s, 1H), 3.86 (d,
2H, J ¼ 8.9 Hz), 3.49 (d, 2H, J ¼ 8.9 Hz). 13C-NMR (CDCl3): ꢀ 141.1,
133.5, 133.4, 133.2, 130.7, 129.7, 129.7, 129.6, 129.5, 122.3, 101.5,
100.5, 84.83, 84.82, 82.51, 82.48, 41.90, 41.88, 47.0, 46.6. MS shows
predominatly the Mþ peak for the retro Diels-Alder product 2-bromo-
3-iodonaphthalene (6).
2-Bromo-3-iodonaphthalene, 6
The procedure described for 5 above, starting from 4 (10.00 g,
11.38 mmol) gave 6 (3.16 g, 9.49 mmol, 83%). One hundred and sixty
two milligrams (2%) starting material was recovered. M.p. 120.1–
120.7ꢀC. H-NMR (CDCl3) ꢀ 8.39 (s, 1H, CH), 8.13 (s, 1H, CH), 7.69
1
(m, 2H, CH), 7.50 (m, 2H, CH). 13C-NMR (CDCl3): ꢀ 139.96, 134.08,
133.65, 131.35, 127.77, 127.41, 127.27, 127.01, 126.49, 98.60. MS: 334,
332 (36%/33% Mþ), 207, 205 (17% M-I), 126 (100% M-BrI).
ACKNOWLEDGMENTS
Financial support from the Royal Institute of Technology and the
Ernst Johnson Foundation is gratefully acknowledged.

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2756
Hellberg, Allared, and Pelcman
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Received in the UK November 12, 2002