Novel reaction of [bis(acyloxy)iodo]arenes

Article abstract of DOI:10.1070/MC2003v013n06ABEH001819

The reaction of [(diacetoxy)iodo]benzene with furazan dicarboxylic acid was accompanied by a novel decarboxylative ring-cleavage reaction; the cyanogen N-oxide, reactive intermediate generated in the process, was dimerised or trapped by a dipolarophile.

Full text of DOI:10.1070/MC2003v013n06ABEH001819

, 2003, 13(6), 277–278
Novel reaction of [bis(acyloxy)iodo]arenes
Aleksei B. Sheremetev* and Svetlana M. Konkina
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russian Federation.
Fax: +7 095 135 5328; e-mail: sab@ioc.ac.ru
10.1070/MC2003v013n06ABEH001819
The reaction of [(diacetoxy)iodo]benzene with furazan dicarboxylic acid was accompanied by a novel decarboxylative ring-
cleavage reaction; the cyanogen N-oxide, reactive intermediate generated in the process, was dimerised or trapped by a dipolaro-
phile.
The chemistry of [bis(acyloxy)iodo]arenes, ArI(OCOR)2, is of
N
considerable interest and excellent reviews on both the syn-
thesis and the reactivity of these compounds were published.1–6
It is well known7 that upon irradiation or heating ArI(OCOAlk)2
undergo decarboxylative decomposition generating alkyl radicals,
which can be effectively trapped with various heteroaromatic
bases, electron-deficient alkenes or disulfides (Scheme 1).
O
Me
O
N
Me
CO2H
Me
CN
NOH
O
O
i
ii
I
Ph
N
N
– PhI
– CO2
O
O
N
1
3
Me
O
N
N
2
R
N
Scheme 2 Reagents and conditions: i, DIB or BTI, chlorobenzene or
CH2Cl2, 40–50 °C; ii, toluene, 100–110 °C.
R''
R''
OCOR
OCOR
hv or heat
R'
R'
R
Ar
I
– ArI
– CO2
The net result of this process corresponds to a formal breaking
of five bonds (as indicated in Scheme 3) with concomitant
generation and dimerization of cyanogen oxide 6. Note that,
previously, nitrile oxide 6 was only generated (i) from α-chloro-
α-cyanoformoxime by base treatment11–13 and (ii) from 3-amino-
furazan carboxylic acid by diazotization.10 1,3-Dipolar cyclo-
addition14 of nitrile oxide 6 generated from carboxylate 5 was
examined with styrene, cyclopentene, cyclohexene, 2,5-dihydro-
furane, and phenylacetylene. The reactions were run by simply
heating a mixture of furazan dicarboxylic acid 4, 5–10 equiv. of
a dipolarophile and DIB in chlorobenzene.‡ The crude products
were isolated from these reactions by chromatography. While a
ca. 70% yield of isoxazolines 8–11§ was obtained from the
olefins, phenylacetylene reacted poorly even at a high con-
centration to furnish at best a 16% isolated yield of izoxazole
12; a complex product mixture was obtained, and the isolation
of target product 12 was difficult to perform. Probably, DIB was
also consumed in side-reactions with phenylacetylene; reactions
of iodine(III) compounds with terminal acetylenes are well
documented.15
Another goal was to obtain 1,2,4-oxadiazoles by the reac-
tions of nitrile oxide 6 with nitriles.14 However, slightly heating
furazan dicarboxylic acid 4 with DIB in an excess of a nitrile
[MeCN, CCl3CN, C(NO2)3CN, or PhCN] afforded only intract-
able product mixtures.
In contrast, acid 4 was recovered from boiling chlorobenzene.
However, the decarboxylation of acid 4 can be carried out in
boiling dichlorobenzene under air atmosphere.¶ Interestingly, the
reaction of acid 4 with styrene under the above conditions gave a
mixture of products that contained cyanoformaldoxime 13 (47%),
isoxazoline 8 (14%), addition products 12 (3%) and 3,7-di-
phenyl-5-cyano-1-aza-2,8-dioxabicyclo[3.3.0]octane 14 (3%)
R
Ar'S SAr'
Ar'S
R
Scheme 1
The chemistry of ArI(OCOR)2, which incorporate a hetero-
cyclic ring as a key structural component R, has never been
published.
We are interested in the chemistry of azoles since the presence
of heteroatoms in such molecules can provide a wider range of
ring opening and rearrangement reactions.8,9 An intriguing pos-
sibility is the use of azolylcarboxylic acids in the synthesis of
respective [bis(azoloyloxy)iodo]arenes whose reactivity is based
on main heterocycle transformations rather than usual radical
reactions. Here, we report on the novel reaction of [bis(acyl-
oxy)iodo]benzenes derived from furazan carboxylic acids.
A variety of [bis(acyloxy)iodo]arenes are usually synthesised
by ligand exchange of commercially available [(diacetoxy)-
iodo]benzene (DIB) or [bis(trifluoroacetoxy)iodo]benzene (BTI)
with corresponding acids.1 When 3-methylfurazan-4-carboxylic
acid 1 was treated with DIB in warm chlorobenzene, target
compound 2† was prepared in a moderate yield of 74%
(Scheme 2). When the reaction was repeated using BTI, com-
pound 2 was obtained in high yield (87%). The decarboxylation
experiment was performed by heating compound 2 in toluene at
100–110 °C until finishing carbon dioxide evolution. α-Hydroxy-
imino nitrile 3 was isolated by chromatography in 65–70%
yield.
In attempting to prepare carboxylate 5 starting with dicar-
boxylic acid 4, we encountered the evolution of carbon dioxide
and the formation of 3,4-dicyanofuroxan 710 (GLPC yield was
84%) and iodobenzene (GLPC yield was 96%) (Scheme 3).
†
‡
Synthesis of [bis(3-methylfurazan-4-oyloxy)iodo]benzene 2. A mixture
General procedure for the generation and trapping of cyanogen oxide
of 3-methylfurazan carboxylic acid (1.28 g, 10 mmol) and DIB (1.61 g,
5 mmol) in chlorobenzene (15 ml) was stirred on a rotary evaporator at
45 °C under reduced pressure (~10 Torr) for 30 min. The reaction mix-
ture was cooled to ambient temperature and diluted with hexane (10 ml).
The precipitate was filtered off and washed with CHCl3 to give 1.69 g
(74%) of 2 as a colourless powder, mp 171–173.5 °C. 1H NMR ([2H6]DMSO)
d: 2.42 (s, 6H, Me), 7.51 (3H, Ph), 8.12 (2H, Ph). 13C NMR ([2H6]DMSO)
d: 8.96 (Me), 125.1 (i-Ph), 130.8 (m-Ph), 131.4 (p-Ph), 133.5 (o-Ph),
149.1 (C–CO2), 152.2 (C–Me), 160.5 (C=O). IR (n/cm–1): 3090, 1670,
1614, 1480, 1405, 1395, 1358, 1303, 1180, 1142, 1018, 996, 920, 835.
Found (%): C, 36.72; H, 2.43; N, 12.17; I, 27.68. Calc. for C14H11IN4O6
(458.17) (%): C, 36.70; H, 2.42; N, 12.23; I, 27.70.
6. To a suspension of furazan dicarboxylic acid 4 (0.02 mol) in a mixture
of chlorobenzene (10 ml) and an olefin (0.1–0.2 mol) at 40–50 °C DIB
(0.011 mol) was added in small portions with stirring. The reaction
mixture was vigorously stirred at the specified temperature until the
complete generation of iodobenzene (according to GLPC). The resulting
solution was cooled, concentrated under reduced pressure, and separated
by silica gel chromatography.
§
All spectroscopic and analytical data were consistent with the struc-
tures assigned. Compounds 7,10 8,11,12 9,12 10,12 11,13 1211 and 1418
corresponded to materials described previously.
¶
Note that decarboxylation of acid 4 was observed at 170 °C/25 Torr.16
The decomposition produced syn-cyanoformaldoxime 13.16,17
– 277 –

, 2003, 13(6), 277–278
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O
O
HO2C
CO2H
1
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N
N
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O
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8
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4
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– PhI
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O
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N
O
9
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CN
N
7
6
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Ph
O
NC
O
11
N
Ph
O
CN
N
CN
N
8
O
O
9
10
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Scheme 3 Reagents and conditions: i, DIB, chlorobenzene, 40–50 °C.
(Scheme 4). Compound 14 is known to result from the reaction
of intermediate furoxan 7 with styrene.18
In conclusion, the ability of [(furazan-4-oyloxy)iodo]benzene
to undergo decarboxylation with simultaneous furazan ring
cleavage is a novel type of [bis(acyloxy)iodo]arene transforma-
tions. This difference in the reactivity of [bis(acyloxy)iodo]-
arenes and [bis(azoloyloxy)iodo]arenes indicates that the pres-
ence of heteroatoms in acyloxy moieties play a crucial role in
determining the overall pathway of the degradation process.
This work was supported by the Russian Foundation for
Basic Research (grant no. 1-03-32944). We are grateful to
Dr. D. E. Dmitriev for carrying out NMR analysis.
CN
CN
i
Ph
8 12
+ + +
Ph
4
N
NOH
O
O
13
14
Scheme 4 Reagents and conditions: i, o-dichlorobenzene, 180 °C.
Received: 2nd July 2003; Com. 03/2145
– 278 –