Preparation and X-ray crystal structure of 2-iodyl-N,N-dialkylaniline oxides: First entry into the heterocyclic system of benziodoxazole

Article abstract of DOI:10.1039/b813163e

The oxidation of 2-iodo-N,N-dialkylanilines with an excess of dimethyldioxirane in acetone affords 2-iodyl-N,N-dialkylaniline oxides, structural features of which are in agreement with the new heterocyclic system of benziodoxazole. The Royal Society of Chemistry.

Full text of DOI:10.1039/b813163e

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Preparation and X-ray crystal structure of 2-iodyl-N,N-dialkylaniline
oxides: first entry into the heterocyclic system of benziodoxazolewz
Viktor V. Zhdankin,* Victor N. Nemykin,* Rashad R. Karimov
and Zeinul-Gabiden Kazhkenov
Received (in Cambridge, UK) 30th July 2008, Accepted 25th September 2008
First published as an Advance Article on the web 20th October 2008
DOI: 10.1039/b813163e
The oxidation of 2-iodo-N,N-dialkylanilines with an excess of
dimethyldioxirane in acetone affords 2-iodyl-N,N-dialkylaniline
oxides, structural features of which are in agreement with the
new heterocyclic system of benziodoxazole.
Hypervalent iodine compounds are employed extensively in
organic synthesis as highly selective and environmentally friendly
oxidizing reagents.1 Especially important are the heterocyclic
iodine(III) and iodine(V) derivatives, known under the common
name of benziodoxoles (structures 1 and 2), which have higher
thermal stabilities and more useful reactivity patterns compared
to the analogous non-cyclic derivatives.2 2-Iodylbenzoic acid
Scheme 1 Preparation of 2-iodyl-N,N-dialkylaniline oxides 5.
(IBX) and 2-iodosylbenzoic acid (IBA) in their cyclic tautomeric
forms 1 (2X = O) and 2 (2X = O, Y = OH) are the best known
Compounds 5a,b were prepared in the form of stable, white
microcrystalline products by the oxidation of 2-iodo-N,N-
dialkylanilines 9a,b with excess dimethyldioxirane in acetone.
The starting anilines 9a,b can be conveniently prepared from
commercially available 2-iodoaniline 6 by acylation to give
amides 7,6 subsequent methylation, and reduction of N-methyl-
amides 8 to give dialkylanilines 9 as outlined in Scheme 1.
Compounds 5 were identified on the basis of spectroscopic
data, ESI mass spectrometry and single crystal X-ray analysis
in the case of 5b.y IR spectra of all compounds showed a
strong IQO absorption at 750–770 cmꢀ1. 1H NMR spectra of
compounds 5 show signals in the aromatic region which look
very similar to the spectrum of IBX 1 (2X = O), as well as the
appropriate signals of the two alkyl groups. In the 13C NMR
spectra of products 5, the signal of C–IO2 is observed at
147–149 ppm, which is typical of iodylarenes.6 The ESI-
HRMS spectrum of compound 5b demonstrated strong peaks
[2M + Na]+ and [2M + H]+ corresponding to a dimer as
well as weaker [M + Na]+ and [M + H]+ peaks. Interestingly
the addition of trifluoroacetic acid to compound 5b leads to
the disappearance of the dimer peaks [2M + Na]+ and [2M +
H]+ leaving only the monomer peak 338.2308 [M + H]+ in
the MS spectrum.
and practically important representatives of benziodoxoles.
Structural aspects of IBX, IBA and other benziodoxoles have
been investigated by several research groups,3,4 most notably by
Katritzky and co-workers in a series of papers published in
1989–1990.4 Besides benziodoxoles, the only other known five-
membered heterocyclic system incorporating hypervalent iodine
is represented by benziodazoles 3.5 In this communication we
report the preparation of 2-iodyl-N,N-dialkylaniline oxides 4,
structural features of which are in agreement with the new
heterocyclic system of benziodoxazole 5.
The solid state structure of compound 5b was established by
single crystal X-ray crystallography (Fig. 1).y The X-ray data
reveal that two crystallographically independent molecules are
present in the crystal unit cell. Selected bond distances, bond
angles and torsion angles for both molecules are listed in
Table 1. The five-membered benziodoxazole ring is present
in both independent molecules and in both cases it is nearly
planar with the maximum observed C–I–O–N torsion angle of
B171. However, the structural parameters, in particular, the
endocyclic I–O bond distances (I2–O3 2.366(10) A and I1–O8
Department of Chemistry and Biochemistry, University of Minnesota
Duluth, Duluth, Minnesota 55812, USA. E-mail: vzhdanki@d.umn.edu;
Fax: +1-218-726-7394; Tel: +1-218-726-6902
w Dedicated to Professor Alan R. Katritzky on the occasion of his
80th birthday.
z Electronic supplementary information (ESI) available: Experimental
details and characterization data, including crystallographic data for
5b. CCDC 696745. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/b813163e
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Fig. 2 Intermolecular interactions between molecules A–D formed
by two pairs of independent molecules in the unit cell found in the
crystal structure of 5b (at the 50% probability level).
Fig. 1 X-Ray crystal structure of two independent molecules of 5b
(at the 50% probability level) in the unit cell. Selected bond distances,
bond angles and torsion angles for both independent molecules are
listed in Table 1.
with each other. Both the I2QO oxygen atoms are involved in
formation of intermolecular bonds, while one of the I1QO
oxygen atoms does not participate in the formation of the
tetramolecular cluster and, as expected, the I1QO5 bond is
significantly shorter.
2.466(9) A), are significantly different. This difference reflects
different intermolecular interactions between the molecules in
the unit cell (Fig. 2). Indeed, two pairs of independent
molecules observed in the unit cell of 5b form a very unusual
cluster in which two pairs of iodine centers (I2(A) and I2(C) as
well as I1(B) and I1(D), Fig. 2) have significantly different
hexacoordinated pseudo-octahedral geometries. As a result,
the five-membered cycle with hexacoordinated iodine I2(A)
and I2(C) centers is more planar as compared to that with
iodine centers I1(B) and I1(D) (Table 1). It is interesting to note
that S enantiomers (molecules A and C, Fig. 2) interact both
with each other as well as with the corresponding R enantio-
mers B and D. On the other hand, R enantiomers B and D
interact only with appropriate S enantiomers A and C but not
A comparison of the endocyclic I–O bond distances and
C–I–O bond angles in 5b (entry 1) with the known pentavalent
iodine heterocycles (entries 2–4) and pseudo-heterocycles
(entries 5–8) is given in Table 2. The I–O bond distances in
the five-membered ring of benziodoxoles are generally found
in the range of 2.26 A (entry 3) to 2.48 A (entry 2). The
structural parameters in molecule 5b are in the middle of
this range, which allows us to classify this molecule as an
iodine(V) heterocycle, in contrast to the previously reported
o-iodylnitrobenzene (entry 5), which belongs to the group of
pseudo-heterocycles (intramolecular I–O bond distances
2.6–2.8 A).
As typical for the known pentavalent iodine heterocycles,1,2
compounds 5 are powerful oxidants toward organic sub-
strates. We have found that compound 5b reacts with various
alcohols (primary and secondary alkyl, cycloalkyl, benzylic
and allylic alcohols) under mild conditions to afford
the respective aldehydes and ketones in excellent yields. The
details of these oxidations are provided in the ESI.z
Table 1 Selected interatomic distances, angles and torsion angles in
two independent molecules of 5b
Distance/A
or angle/1
Distance/A
or angle/1
Bond
Bond
I1–O8
I1–O5
I1–O7
O8–N6
C14–I1–O8
O5–I1–O8
O5–I1–O7
O7–I1–O8
C14–I1–O8–N6
2.466(9)
1.745(12)
1.836(10)
1.374(14)
69.8(5)
I2–O3
I2–O4
I2–O9
O3–N10
C19–I2–O3
O4–I2–O3
O4–I2–O9
O9–I2–O3
C19–I2–O3–N10
2.366(10)
1.771(11)
1.807(10)
1.407(14)
70.8(4)
In conclusion, we have reported the preparation of 2-iodyl-
N,N-dialkylaniline oxides, structural features of which are in
agreement with the new heterocyclic system of benziodoxa-
zole. These new pentavalent iodine heterocycles can be used as
efficient oxidizing reagents for the selective oxidation of
alcohols to the respective carbonyl compounds.
90.5(5)
91.1(4)
101.7(5)
159.9(4)
17.39
101.9(5)
160.8(4)
11.50
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Table 2 Endocyclic I–O bond distances and C–I–O bond angles in
hypervalent iodine heterocycles (entries 1–4) and pseudo-heterocycles
(entries 5–8)
b = 82.16(3), g = 78.02(3)1, V = 1261.1(5) A3, Z = 4, m(Mo Ka) =
2.532 mmꢀ1, T = 298 K, 4478 reflections measured, 4429 unique; final
R1 = 0.0698 (I Z 2s(I)), Rw = 0.0886 (I Z 2s(I)); Rint = 0.00.
CCDC 696745.
I–O
C–I–O
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This work was supported by a research grant from the
National Science Foundation (CHE-0702734).
Notes and references
y Crystal data for 5b. C11H16INO3: M = 337.15, triclinic, space group
P1, a = 8.1788(16), b = 10.512(2), c = 15.850(3) A, a = 71.58(3),
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This journal is The Royal Society of Chemistry 2008
Chem. Commun., 2008, 6131–6133 | 6133