An efficient approach for the conversion of oximes into carbonyl compounds using dichloramine-T

Article abstract of DOI:10.1055/s-2007-983731

An efficient approach for the conversion of oximes into the corresponding carbonyl compounds using dichloramine-T is described. The reaction was performed in acetonitrile in the presence of small amount of water. In comparison to reported oxidative deoximating agents, the reaction was rapid and gave good yields of the products. The conversion was found to be chemoselective and during the reaction sensitive groups, like phenolic and C=C bonds, remained intact. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2007-983731

1930
SHORT PAPER
An Efficient Approach for the Conversion of Oximes into Carbonyl
Compounds Using Dichloramine-T
C
onversion of
r
O
ximes
a
into Carbo
d
C
ompoun
e
ds
U
sing D
e
ichloramin
p
e-T K. Gupta, Laxmi Manral, Kumaran Ganesan*
Defence Research & Development Establishment (DRDE), Gwalior (MP) 474002, India
Fax +91(751)2341148; E-mail: pr_14@rediffmail.com
Received 30 March 2007; revised 27 April 2007
oxime in comparable yield, longer reaction times are re-
Abstract: An efficient approach for the conversion of oximes into
the corresponding carbonyl compounds using dichloramine-T is de-
scribed. The reaction was performed in acetonitrile in the presence
of small amount of water. In comparison to reported oxidative deox-
quired. The results of the deoximation of benzophenone
oxime with dichloramine-T is compared to reported re-
sults for various reagents from the literature in
imating agents, the reaction was rapid and gave good yields of the Table 1.2b,f,4–8
products. The conversion was found to be chemoselective and dur-
To further prove the utility of dichloramine-T as a deoxi-
ing the reaction sensitive groups, like phenolic and C=C bonds, re-
mained intact.
mating reagent, a variety of oximes were deoximated with
dichloramine-T (Table 2). Mechanistically, the reaction
of dichloramine-T with oxime proceeds with the initial
electrophilic attack of positive chlorine provided by
dichloramine-T on the oximic nitrogen. Subsequent nu-
cleophilic addition of water followed by elimination of
chlorohydroxylamine gives the target compound
(Scheme 1).
Key words: dichloramine-T, oximes, carbonyl compounds, aceto-
nitrile, chemoselective
Oximes are a very important class of organic compounds
that have been used for the purification and characteriza-
tion for carbonyl compounds.1 Thus, they have been used
as a protecting group for carbonyl compounds. The re-
verse process, i.e., regeneration of carbonyl compounds
from oximes, has also been studied and reviewed exten-
sively and a large number of reagents have been devel-
oped.2 These methods, however, suffered from
disadvantages such as long reaction times, harsh reaction
conditions,3 difficulties in product purification,4 and low
product yields.2b Moreover, the majority of these agents
are oxidative in nature and, hence, the formation of over-
oxidized products is a serious problem.2b In the course of
our investigations, we have found that dichloramine-T
(N,N-dichloro-4-toluenesulfonamide, DCT) can be used
as an efficient reagent for the conversion of oximes into
the corresponding carbonyl compounds. Dichloramine-T
is a convenient source of positive chlorine and is widely
used as a chlorinating agent. To the best of our knowl-
edge, there are no reports of the use of this reagent as a
deoximating agent and, herein, we report our results on
the use of dichloramine-T for the conversion of oximes
into their corresponding carbonyl compounds.
Cl
R1
R2
Cl
Ts
N
H2O
– H+
Cl
N
+
R1
OH
N
R2
OH
R1
Cl
R1
R2
– (ClNHOH)
HO
N
O
R2
OH
Scheme 1
It can be inferred that the rate of the deoximation reaction
will depend on the availability of the lone pair of electrons
on the oximic nitrogen, which ultimately depends on the
nature of the substituents attached to the oximic carbon.
For this reason, ketoximes having two electron-donating
alkyl groups were found to react faster than aldoximes
(Table 2, entry 1 vs entry 6). In the case of aromatic
oximes, the resonance of the oximic double bond with the
benzene ring decreases the nucleophilicity of the oximic
nitrogen, which retards the rate of the reaction (Table 2,
entries 6–8), therefore, longer reaction times were re-
quired for such oximes. The presence of electron-with-
drawing groups on the benzene ring further reduces the
rate of deoximation (Table 2, entry 7). Dichloramine-T
was found to be selective for the conversion of oximes to
carbonyl compounds and no byproduct formation was ob-
served. Unlike other reported deoximating agents,
dichloramine-T is not oxidative in nature. Hence, the for-
mation of overoxidized product was not detected
Initially, we examined the reaction of benzophenone
oxime with dichloramine-T. The reaction was carried out
in acetonitrile at room temperature; a small amount of wa-
ter was also required for completion of the reaction. The
reaction was very fast and gave a quantitative yield of
benzophenone. It is evident that among all the deoximat-
ing reagents, dichloramine-T was the fastest and most ef-
ficient (Table 1). Although other deoximating reagents
are known that give benzophenone from benzophenone
SYNTHESIS 2007, No. 13, pp 1930–1932
x
x.
x
x
.
2
0
0
7
Advanced online publication: 18.06.2007
DOI: 10.1055/s-2007-983731; Art ID: Z08407SS
© Georg Thieme Verlag Stuttgart · New York

SHORT PAPER
Conversion of Oximes into Carbonyl Compounds Using Dichloramine-T
1931
Table 1 Deoximation of Benzophenone with Various Reagents
Entry
Reagent
Time
1 min
4.5 h
3 h
Yield (%)
Ref.
–
1
2
3
4
5
6
7
8
dichloramine-T (TsNCl2)
95
98
pyridinium dichromate (PDC)
chlorotrimethylsilane (TMSCl)
1,3-dichloro-5,5-dimethylhydantoin (DCDMH)
4
98
5
2 h
82
6
cetyltrimethylammonium permanganate {[Me(CH2)15]Me3N+ MnO4 , CTAP}
40 min
20 min
10 min
5 min
95
7
–
o-iodoxybenzoic acid (IBX)
92
2b
2f
8
Dess–Martin periodinane (DMP)
100
86
thallium trinitrate [Tl(NO3)3, TTN]
(checked by TLC and GC-MS). The usefulness of this re- trogen was considerably reduced because of intramolecu-
agent was further demonstrated by the good to excellent lar hydrogen bonding or extended conjugation,
yield of products obtained during deoximation of cyclic respectively. With such oximes, longer reaction times
(Table 2, entry 2) and sterically hindered (Table 2, entry with refluxing are required to give better yield of the prod-
10) oximes in shorter reaction times. The reaction took uct. However, dichloramine-T showed excellent
place at room temperature with all the ketoximes, but with chemoselectivity during these reactions and phenolic
aldoximes and less reactive oximes, refluxing conditions group and C=C bonds remained intact.
were required.
In conclusion, dichloramine-T was found to be an effi-
The reagent was found to work less efficiently with the cient reagent for the conversion of oximes into their cor-
substrates like salicylaldehyde oxime (Table 2 entry 8) responding carbonyl compounds. The conversion was
and cinnamaldehyde oxime (Table 2, entry 9) where the very efficient, fast, and gave better yields of the product in
availability of the lone pair of electron on the oximic ni- comparison to previously reported deoximating reagents.
The reagent is very mild and byproducts and overoxida-
tion products were not formed. The peculiarity of
dichloramine-T as deoximating reagent lies in the fact that
sensitive functional groups also survived after the reac-
tion. In addition, during the reaction process, dichloram-
ine-T was converted into the 4-toluenesulfonamide,
which can easily be separated from the reaction mixture
and reconverted into dichloramine-T and thus can be re-
cycled.
Table 2 Conversion of Oximes into the Corresponding Carbonyl
Compounds in the Presence of Dichloramine-T
R1
R1
dichloramine-T
MeCN–H2O
N
O
R2
OH
R2
Entry R1
R2
Temp
r.t.
Time
1 min
1 min
1 min
1 min
1 min
4 h
Yielda (%)
1
2
Me
Me
98
97
97
95
96
84
77
89
79
97
The carbonyl compounds formed were characterized by their phys-
ical data, which were in accord with values reported in the literature,
and GC-MS analysis.
(CH2)5
Ph
r.t.
3
Me
Ph
r.t.
4
Ph
r.t.
Conversion of Oximes into Carbonyl Compounds: General
Procedure
5
4-ClC6H4
Ph
Me
H
reflux
reflux
reflux
reflux
reflux
reflux
To the soln of oxime (10 mmol) in MeCN containing small amount
of H2O (2%) was added dichloramine-T (10 mmol) and the resulting
mixture was stirred until the reaction was complete (monitored by
TLC and GC). The solvent was evaporated on rotary evaporator and
the crude product was purified by flash chromatography (hexane–
EtOAc, 9:1).
6
7
2-ClC6H4
2-HOC6H4
CH=CHPh
camphor
H
6 h
8
H
8 h
9
H
5 h
Acknowledgements
10
1 h
Authors thank Er. K. Sekhar, Director, Defence Research and De-
velopment Establishment, Gwalior for his keen interest and encou-
ragement. We sincerely thank Dr. D. K. Dubey and Dr. P. K. Gutch
for their support.
a All the products were characterized by GC-MS and compared to au-
thentic samples.
Synthesis 2007, No. 13, 1930–1932 © Thieme Stuttgart · New York

1932
P. K. Gupta et al.
SHORT PAPER
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