Facile and chemoselective microwave-assisted cleavage of oximes to their corresponding carbonyl compounds using N,N′-dibromo-N,N′-1,3- propylene-bis[(4-methylphenyl)sulfonamide] as a deoximating reagent

Article abstract of DOI:10.1055/s-2004-834880

Aldoximes and ketoximes are converted to the parent carbonyl compounds in good yields when treated with N,N′-dibromo-N,N′-1,3-propylene- bis[(4-methylphenyl)sulfonamide] (2) under microwave irradiation. The simple workup minimizes the loss of product and oximes have been selectively oxidized in the presence of alcohols and alkenes.

Full text of DOI:10.1055/s-2004-834880

2784
SHORT PAPER
Facile and Chemoselective Microwave-Assisted Cleavage of Oximes to Their
Corresponding Carbonyl Compounds Using N,N¢-Dibromo- N,N¢-1,3-
propylene-bis[(4-methylphenyl)sulfonamide] as a Deoximating Reagent
N
,
N
¢
-Dibromo-
N,
N
r
¢
-1,3-pr
o
d
pylene-bis[(
e
4-methylph
s
enyl)sulfo
h
namide] ir Khazaei,* Abbas Amini Manesh, Amir Hoshang Ghasemi
Department of Chemistry, Faculty of Sciences, Bu-Ali Sina University, P. O. Box 65178-4119, Hamadan, Iran
E-mail: khazaei_1326@yahoo.com
Received 11 June 2004; revised 3 August 2004
R1
R1
R2
acetone/H2O
MW
Abstract: Aldoximes and ketoximes are converted to the parent
carbonyl compounds in good yields when treated with N,N¢-dibro-
mo-N,N¢-1,3-propylene-bis[(4-methylphenyl)sulfonamide] (2) un-
der microwave irradiation. The simple workup minimizes the loss
of product and oximes have been selectively oxidized in the pres-
ence of alcohols and alkenes.
N
OH
+
2
O
+
1
R2
Scheme 2
Microwave irradiation of a solution of oximes in aqueous
acetone in the presence of title reagent 2 gave the corre-
sponding carbonyl compounds in good yields (Scheme 2).
Key words: aldoximes, carbonyl compounds, ketoximes, micro-
wave irradiation, selective
The results of the conversions of various oximes to their
corresponding carbonyl compounds are presented in Ta-
ble 1.
Oximes are easily obtained from carbonyl compounds and
have great potential as intermediates in organic synthesis.1
They are also useful protecting groups in multistep organ-
ic syntheses2 and have found extensive application in the
isolation of carbonyl compounds.3 Their synthesis from
non-carbonyl compounds offers an alternative route to al-
dehydes and ketones.4,5 A good number of methods based
on hydrolytic,6 reductive,7 and oxidative8 reactions have
been developed for their deoximation. In spite of the many
reagents available, there is still scope for newer reagents
as the existing oxidative methods suffer from one or the
other disadvantages such as long reaction times,9 difficul-
ties in isolation of products,5 and formation of over oxida-
tion products leading to low yields.
A sterically hindered ketone oxime (entry 13) was also
oxidatively cleaved to the corresponding ketone in good
yield. The aldoximes were converted to the corresponding
aldehydes and no carboxylic acid was formed due to over-
oxidation of the regenerated aldehyde (entries 3, 4, 7, 10
and 15). This procedure is also useful for the chemoselec-
tive oxidative deoximation of oximes in the presence of
alcohols or for oximes that contain an OH functional
group (entry 12). Thus, when equimolar mixtures of ben-
zophenone oxime and benzyl alcohol in acetone and water
were allowed to react with title reagent 2 under micro-
wave irradiation, the ketoxime underwent oxidative deox-
imation chemoselectively, giving (91%) benzophenone,
whereas the benzyl alcohol was recovered unchanged
(Scheme 3).
Advantages such as cleaner reactions, very short reaction
times, and ease in workup have kindled a special interest
in microwave chemistry.10 We now report a new oxidative
method for the selective cleavage of oximes to their car-
bonyl compounds under microwave irradiation using
N,N¢-dibromo-N,N¢-1,3-propylene-bis[(4-methylphe-
nyl)sulfonamide] (2) as an effective oxidizing agent that
overcomes the disadvantages associated with oxidative
methods developed so far. The title reagent was prepared
An unsaturated oxime (entry 15) was cleaved to the corre-
sponding unsaturated aldehyde without affecting the dou-
ble bond. We also observed the competitive oxidation of
oximes in the presence of an alkene. In a control experi-
ment, when equimolar mixtures of ethyl methyl ketone
oxime and cyclohexene in acetone and water were al-
lowed to react with the title reagent 2, under microwave
irradiation, the ketone oxime underwent chemoselectively
from
N,N¢-1,3-propylene-bis[(4-methylphenyl)sulfon-
amide] (1) (Scheme 1).11
CH3
CH3
H3C
H3C
H
N
H
N
Br
N
Br
N
+ 2 Br2
- 2 HBr
S
S
S
S
O2
O2
O2
O2
1
2
Scheme 1
SYNTHESIS 2004, No. 17, pp 2784–2786
x
x.
x
x
.
2
0
0
4
Advanced online publication: 15.10.2004
DOI: 10.1055/s-2004-834880; Art ID: Z12204SS
© Georg Thieme Verlag Stuttgart · New York

SHORT PAPER
N,N¢-Dibromo-N,N¢-1,3-propylene-bis[(4-methylphenyl)sulfonamide] as Deoximating Agent
2785
Table 1 Deoximation with 2 under MW Irradiation
Entry
1
Substrate
Product
Time (min)
Yield (%)a,b
cyclohexanone oxime
acetophenone oxime
cyclohexanone
acetophenone
1
98
94
93
92
92
92
92c
91
91
90
90
85
84
84
83
2
1
3
benzaldehyde oxime
benzaldehyde
1
4
4-chlorobenzaldehyde oxime
benzophenone oxime
4-methylacetophenone oxime
isobutyraldehyde oxime
isobutyl methyl ketone oxime
diisopropyl ketone oxime
2-chlorobenzaldehyde oxime
ethyl methyl ketone oxime
benzoin oxime
4-chlorobenzaldehyde
benzophenone
1
5
1.1
1.1
1.2
1.5
1.6
2
6
4-methylacetophenone
isobutyraldehyde
isobutyl methyl ketone
diisopropyl ketone
2-chlorobenzaldehyde
ethyl methyl ketone
benzoin
7
8
9
10
11
12
13
14
15
2
2
camphor oxime
camphor
2.5
2.5
2
cyclopentanone oxime
cinnamaldehyde oxime
cyclopentanone
cinnamaldehyde
a Products were characterized by their physical constants, comparison with authentic samples and melting points of 2,4-dinitrophenylhydrazone
derivatives and by their IR and 1H NMR spectra.
b Isolated yields.
c CH2Cl2/H2O was used as reaction solvent.
Ph
Ph
Ph
Ph
+ 2 , acetone, H2O
N
+
-CH2OH
+
-CH2OH
O
MW
OH
Unchanged
alkohol
Ketone
91%
99%
Scheme 3 Selective deoximation in the presence of benzyl alcohol.
oxidative deoximation giving 89% ethyl methyl ketone, products, due to the high chemoselectivity and mild na-
whereas the cyclohexene was recovered unchanged ture of title reagent 2; easy workup procedure; and high
(Scheme 4).
yields. The OH functional group in the oxime structure
does not get oxidized to a carbonyl functional group, and
the debrominated product 1 can be converted to 2 and re-
used several times.
At the end of the reaction, N,N¢-dibromo-N,N¢-1,3-propy-
lene-bis[(4-methylphenyl)sulfonamide] (2) was convert-
ed to the N,N¢-1,3-propylene-bis[(4-methyl-phenyl)-
sulfonamide] (1), which can be isolated, brominated, and
reused as deoximating reagent.
IR and 1H NMR spectra were recorded using a Shimadzu 435-U-04
spectrophotometer (KBr pellets) and a 90 MHz Jeol FT-NMR spec-
trometer, respectively. 1H NMR chemical shifts were measured rel-
ative to TMS (int; 1H).
In conclusion, the striking features of our method are:
very short reaction times; no formation of over oxidation
H3C
H3C
N,N¢-1,3-Propylene-bis[(4-methylphenyl)sulfonamide] (1)
4-Methylbenzenesulfonyl chloride (20.0 g, 105 mmol) was placed
in a beaker and heated on a water bath (80 °C) until it became a liq-
uid. 1,2-Diaminoethane (4.37 mL, 53 mmol) was then added drop-
wise and the mixture was stirred with a glass rod. The mixture was
heated (80 °C) and stirred for 30 min. The mixture was cooled and
distilled H2O (100 mL) was added. The product was collected by
+ 2 , acetone, H2O
N
+
OH
+
O
MW
H5C2
H5C2
Unchanged
alkene
99%
89%
Scheme 4 Chemoselective deoximation in the presence of cyclohe-
xene.
Synthesis 2004, No. 17, 2784–2786 © Thieme Stuttgart · New York

2786
A. Khazaei et al.
SHORT PAPER
suction on a Büchner funnel, and washed with a little cold H2O and
recrystallized from EtOH; yield: 19.1g (95%); mp 139–140 °C.
IR (KBr): 3272, 2934, 1596, 1464, 1325, 1158, 1089, 816 cm–1.
1H NMR (acetone-d6/TMS): d = 1.63 (m, 2 H), 2.36 (s, 6 H), 2.88
(t, 4 H), 6.32 (br, 2 H), 7.37–7.62 (m, 8 H).
der reduced pressure, and Et2O (20 mL) was added to the mixture,
and stirred for 10 min. Then the sulfonamide 1, was removed by fil-
tration and the product was purified by column chromatography
(hexane–Et2O) (Table 1).
Products (aldehydes and ketones) were characterized by their phys-
ical constants, by comparison with authentic samples, and the melt-
ing points of 2,4-dinitrophenylhydrazone derivatives and by their
IR and 1H NMR spectra.
Anal. Calcd for C17H22N2O4S2: C, 53.38; H, 5.80; N, 7.32. Found:
C, 53.50; H, 6.00; N, 7.45%.
N,N¢-Dibromo-N,N¢-1,3-propylene-bis[(4-methylphenyl)sul-
fonamide] (2)
References
The sulfonamide 1 (10.0 g, 26 mmol) was dissolved in a slight mo-
lar excess of chilled aq NaOH solution (ca. 3 M) at r.t. and the solu-
tion was transferred to a beaker. A solution of Br2 (2.68 mL, 52
mmol) in CCl4 (6 mL) was added to the solution with vigorous stir-
ring. Immediately a yellow precipitate began to form. The yellow
precipitate was collected by suction on a Büchner funnel, washed
with cold distilled H2O (30 mL), and then dried in a vacuum desic-
cator at r.t. for 6 h; yield: 11.7g (83%). The product was stable at r.t.
and not sensitive to air.
IR (KBr): 2922, 1592, 1436, 1350, 1161, 812 cm–1.
1H NMR (acetone-d6/TMS): d = 1.62 (m, 2 H), 2.35 (s, 6 H), 2.87
(t, 4 H), 7.36–7.63 (m, 8 H).
(1) Sandler, S. R.; Karo, W. Organic Functional Group
Preparations, 2nd ed., Vol. 3; Academic Press: San Diego,
1989, 431–476.
(2) Green T. W., Wuts P. G. M.; Protective Groups in Organic
Synthesis; Wiley: New York, 1991; 2nd ed., 214.
(3) Donaruma, L. G.; Heldt, W. Z. Org. React. 1960, 11, 1.
(4) Olah, G. A.; Liao, Q.; Lee, S. C.; Surya Perakash, G. K.
Synlett 1993, 427.
(5) Drabowicz, J. Synthesis 1980, 125.
(6) Donaldson, R. E.; Saddler, J. C.; Boyrn, S.; Mckenzie, A. T.;
Fuchs, P. L. J. Org. Chem. 1983, 48, 2167.
(7) Corey, E. J.; Hopkins, P. B.; Kim, S.; Kou, S.; Nambiar, K.
P.; Flack, J. R. J. Am. Chem. Soc. 1979, 1901, 7131.
(8) Curran, D. P.; Brill, J. F.; Rakiewicz, D. M. J. Org. Chem.
1984, 49, 1654.
Anal. Calcd for C17H20Br2N2O4S2: C, 37.80; H, 3.73; N, 5.18.
Found: C, 37.94; H, 3.90; N, 5.30.
(9) Barhate, N. B.; Gajare, A. S.; Wakharkar, R. D.; Sudalai, A.
Tetrahedron Lett. 1997, 38, 653.
(10) Loupy, A.; Bram, G.; Villemin, D. Solid Support and
Catalysts in Organic Synthesis ; Smith, K., Ed.; Ellis-
Harwood: Chichester UK, 1992, Chap. 12, 302–326.
(11) Khazaei, A.; Shirdarreh, A. Synth. Commun. 1999, 29, 4079.
Deoximation of Oximes; General Procedure
A mixture of the oxime (3 mmol) and 2 (973 mg, 1.8 mmol), in ac-
etone (10 mL) and H2O (1 mL) was introduced in a flask and re-
fluxed under microwave irradiation in a microwave oven at a power
output of 200 W for the appropriate time as indicated in Table 1. Af-
ter completion of the reaction (TLC), the solvent was removed un-
Synthesis 2004, No. 17, 2784–2786 © Thieme Stuttgart · New York