Deprotection of oximes using lodosobenzene in the presence of β-cyclodextrin in water

Article abstract of DOI:10.1080/00397910500522314

A mild and efficient method for the regeneration of carbonyl compounds from oximes at room temperature in impressive yields has been developed using iodosobenzene/KBr in the presence of β-cyclodextrin in water. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910500522314

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Deprotection of Oximes using Iodosobenzene
in the Presence of β‐Cyclodextrin in Water
a
a
a
a
M. Narender , M. Somi Reddy , N. Srilakshmi Krishnaveni , K. Surendra
a
a
,
a
Y. V. D. Nageswar & K. Rama Rao
Organic Chemistry Division‐I, Indian Institute of Chemical Technology,
Hyderabad, India
Published online: 16 Aug 2006.
To cite this article: M. Narender , M. Somi Reddy , N. Srilakshmi Krishnaveni , K. Surendra , Y. V. D. Nageswar
K. Rama Rao (2006) Deprotection of Oximes using Iodosobenzene in the Presence of β‐Cyclodextrin in
&
Water, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 36:10, 1463-1470
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Synthetic Communications , 36: 1463–1470, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500522314
Deprotection of Oximes using
Iodosobenzene in the Presence of
b-Cyclodextrin in Water
M. Narender, M. Somi Reddy, N. Srilakshmi Krishnaveni,
K. Surendra, Y. V. D. Nageswar, and K. Rama Rao
Organic Chemistry Division-I, Indian Institute of Chemical Technology,
Hyderabad, India
Abstract: A mild and efficient method for the regeneration of carbonyl compounds
from oximes at room temperature in impressive yields has been developed using
iodosobenzene/KBr in the presence of b-cyclodextrin in water.
Keywords: b-Cyclodextrin, iodosobenzene, KBr, oximes, water
INTRODUCTION
Oximes are highly stable, can be readily prepared, and are used extensively for
[1]
the protection of carbonyl compounds. There is continued interest for
generating carbonyl compounds from oximes because these can be prepared
from noncarbonyl precursors and can be used for the protection and purifi-
[
2]
cation of carbonyl compounds
[
and the preparation of amides via
3]
Beckman rearrangements. Oxime represents a series of derivatives for the
classical identification of carbonyl compounds, as exemplified by the
[
4]
synthesis of erythromycin derivative. Because oximes could be prepared
from noncarbonyl starting materials, for example, with the Barton
Received in India October 17, 2005
IICT Communication No. 051010.
Address correspondence to K. Rama Rao, Organic Chemistry Division-I, Indian
Institute of Chemical Technology, Hyderabad 500 007, India. Tel.: þ 91-40-
27193164; Fax: þ91-40-27160757; E-mail: drkrrao@yahoo.com
1
463

1
464
M. Narender et al.
[
5]
reaction, their conversion to carbonyl functionality is important from a
synthetic point of view. In view of the importance of deoximation, several
methods have been developed for the cleavage of oximes, such as acid-
[
6]
[7]
[8]
catalyzed hydrolysis,
supported ferricnitrite,
oxidative reaction,
reductive reaction,
[10]
zirconium bis phenyl phosphonate,
clay-
N-halo
[
9]
[
11]
[7c]
[12]
amides,
PCC/H O ,
o-iodoxy benzoic acid/water/DMSO–THF,
2
2
[13]
and CrO /chlorotrimethylsilane. Different approaches reported have
been shown to have various limitations such as hazardous reagents and
3
[14]
solvents, higher temperatures, longer reaction times, and lower yields,
thus limiting their utility in a synthetic sequence especially for large-scale
synthesis. Therefore, there is need to develop a mild and high-yielding
protocol for the deoximation of oximes under aqueous conditions with
potential industrial applications.
In our efforts to develop biomimetic approaches involving cyclodextrins
we explored the deoximation of oximes
[15]
through supramolecular catalysis,
using iodosobenzene with water as solvent. Cyclodextrins are cyclic oligosac-
charides, which exert a microenvironmental effect. They catalyze reactions by
supramolecular catalysis through noncovalent bonding involving reversible
formation of host–guest complexes as seen in enzymes. Complexation
depends on the size, shape, and hydrophobicity of the guest molecule. The
main forces operating in the complexation process are van der Waals hydro-
phobic interactions and hydrogen bonding between the guest and cyclodextrin
(
Figure 1). Thus, the mimicking of biochemical selectivity, which exhibits
shape and substrate selectivity with the reactions carried out in water, will
be superior to chemical selectivity.
RESULTS AND DISCUSSION
Among various oxidizing agents, iodosobenzene, a hypervalent iodine
reagent, attracted our attention because of its low toxicity and high selectiv-
[
16]
ity.
We report herein the first examples of the deoximation of various
oximes 1 to carbonyl compounds 2 under supramolecular catalysis with
b-cyclodextrin using iodosobenzene/KBr in water (Scheme 1).
Figure 1. Supramolecular catalysis of deprotection of oximes using IOB/KBr.

Deprotection of Oximes
1465
Scheme 1.
The reactions were carried out by dissolving b-cyclodextrin in water,
followed by the addition of oxime and iodosobenzene/KBr at room tempera-
ture. The yields obtained were impressive, ranging up to 92%. The yields from
oximes with an aromatic moiety were comparatively better than those from
the saturated ones. This methodology is also compatible with functionalities
such as halo, nitro, hydroxy, methoxy, methylenedioxy, isopropoxy, and
conjugated double bonds (Table 1).
Though phenolic –OH groups are known to undergo oxidation with iodo-
[
17]
sobenzene,
they could survive in the present reaction conditions under
supramolecular catalysis without any oxidation (Table 1, entries 5 and 15;
Scheme 2). Because this is an interesting observation, we further investigated
the tolerance of phenolic –OH under the present reaction conditions by taking
p-hydroxyacetophenone oxime as an example (Table 1, entry 15). The
1
mechanism of supramolecular catalysis was investigated with the help of H
1
NMR spectroscopy as follows: a comparison of the H NMR spectra (D O)
2
of b-cyclodextrin, b-cyclodextrin-p-hydroxyacetophenone oxime, and the
freeze-dried reaction mixture (6 h) was undertaken. Figure 2 shows that
there is an upfield shift of H (0.034 ppm) and H (0.025 ppm) protons of
3
5
b-cyclodextrin in b-cyclodextrin-oxime complex (Figure 2B) as compared
to b-cyclodextrin, indicating the formation of an inclusion complex of
[
18]
oxime with b-cyclodextrin.
It is further observed from the spectrum of
the reaction mixture that apart from subtle changes in the upfield character
of H3 and H5 protons, there is also an upfield shift of the H6 proton
(0.060 ppm). This indicates the complexation of iodosobenzene (IOB) from
the primary side of the b-cyclodextrin. Thus, it could be seen from these
studies that the IOB from the primary side attacks the oxime, which is
elegantly set from the secondary side in the hydrophobic cavity of the b-cyclo-
dextrin. Because in this type of situation under supramolecular catalysis the
phenolic group of the oxime will be away from IOB, hence it does not
undergo oxidation under the reaction conditions (Figure 1).
b-Cyclodextrin (b-CD) was used as a catalyst because it is easily accessible
and inexpensive. b-CD was used only in a catalytic amount. These deoximation
reactions do not take place in the absence of b-cyclodextrin.
The role of CD appears to be to activate not only the oxime but may
also to form a CD–iodosobenzene complex through hydrogen bonding,
which then oxidizes the oxime to the corresponding carbonyl compound. In
these reactions, the b-CD has also been recovered and reused.

1
466
M. Narender et al.
Table 1. Deprotection of oximes with iodosobenzene/KBr in water in the presence
of b-CD
a
b
Entry
Substrate
Product
% Yield
1
92
2
3
4
90
92
86
5
6
88
90
7
8
90
91
9
88
1
1
0
1
84
90
1
2
92
(
continued)

Deprotection of Oximes
1467
Table 1. Continued
a
b
Entry
Substrate
Product
% Yield
1
3
4
91
92
1
1
1
5
6
88
89
1
1
7
8
86
84
a
b
All products were identified by IR, NMR, and mass spectroscopy.
Yields of products isolated after columm chromatography.
Scheme 2.

1
468
M. Narender et al.
Figure 2. A:b-CD, B:b-CD 4- hydroxyacetophenoneoxime, and C: reaction mixture
after 6 h.
Thus, in conclusion, we have presented a simple and efficient method-
ology for the deprotection of oximes even in the presence of sensitive func-
tionalities prone to oxidation. This methodology, involving cyclodextrin in
water with iodosobenzene as an oxidizing agent, has several advantages
over the existing methodologies.
EXPERIMENTAL
General
1
All of the products were characterized by a comparison of their H NMR, IR,
mass, TLC, and physical data (melting and boiling points) with authentic
samples and known compounds.
[19]
All yields of products were isolated
after column chromatography. All reactions were carried out without any
special precautions in an atmosphere of air. Chemicals and solvents were
purchased from Fluka, Aldrich, and S. D. Fine Chemicals and used as

Deprotection of Oximes
1469
1
received. H NMR spectra were obtained on a Gemini 200- or 300-MHz
spectrometer. IR spectra were recorded on a Nicolet FT-IR spectrometer.
Mass spectra were observed on V.G. Auto spectrometer.
Deprotection of Oximes using Iodosobenzene in the Presence of
b-Cyclodextrin in Water
Oxime (1 mmol) dissolved in acetone (2 mL) was added to a solution of b-CD
(
(
0.1 mmol) in distilled water (15 mL) at room temperature. Iodosobenzene
1 mmol) was added, followed by the addition of KBr (0.1 mmol), and
stirring was continued at room temperature for 12 h. The product was
extracted with ethyl acetate (3 ꢀ 15 mL): the organic phase was dried with
anhydrous sodium sulphate and concentrated under vacuum. The crude
product thus obtained was purified by column chromatography on silica gel
(60–120 mesh) using ethyl acetate/hexane (9:1) as eluent.
ACKNOWLEDGMENTS
We thank Council for Scientific and Industrial Research (CSIR), New Delhi,
India, for fellowships to M. N., M. S. R., and K. S.
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