Mild and efficient deprotection of 1,3-dithianes with N,N′-diiodo-N, N′-1,2-ethanediyl-bis(p-toluenesulphonamide)

Article abstract of DOI:10.1002/jccs.200500049

Aliphatic and aromatic 1,3-dithiane are oxidized to the corresponding carbonyl compounds in good yields under mild conditions by N,N′-diiodo-N, N′-1,2-ethanediyl-bis(p-toluenesulphonamide) [NIBTSl and silver nitrate.

Full text of DOI:10.1002/jccs.200500049

Journal of the Chinese Chemical Society, 2005, 52, 327-330
327
Mild and Efficient Deprotection of 1,3-Dithianes with
N,N¢-Diiodo-N,N¢-1,2-Ethanediyl-bis(p-toluenesulphonamide)
Ramin Ghorbani-Vaghei* and Mohammad Ali Zolfigol
Department of Chemistry, Faculty of Science, Bu-Ali Sina University, Hamadan, Iran
Aliphatic and aromatic 1,3-dithiane are oxidized to the corresponding carbonyl compounds in good
yields under mild conditions by N,N¢-diiodo-N,N¢-1,2-ethanediyl-bis(p-toluenesulphonamide) [NIBTS] and
silver nitrate.
Keywords: Deprotection; Oxidation; Carbonyl compounds; NIBTS.
INTRODUCTION
1,3-Dithianes are often used as carbonyl protecting
Aliphatic and aromatic 1,3-dithianes were found to be
oxidized to aldehydes and ketones using NIBTS/AgNO3 in
aqueous acetonitrile at room temperature (Scheme I).
The advantages of NIBTS are as follows:
groups1 or as masked acylanions2 in organic synthesis. Hence,
the deprotection of 1,3-dithianes to regenerate the carbonyl
compound is an important synthetic transformation. 1,3-
Dithianes are considerably more stable than the correspond-
ing O,O-acetals and 1,3-oxathiolanes under acidic condi-
tions. As with most protecting groups, therefore, many of
methods should be available for the deprotection of 1,3-
dithianes.2 Among the various reagents employed for this
purpose are dimethylsulfoxide in the presence of iodine3 or
t-butyl chloride,4 N-halosuccinimide,5 dinitrogen tetroxide
complexes of iron(III) and copper(II) nitrates,6 DDQ,7 tellu-
rium tetrachloride,8 dimethylsulfoxide,9 N-fluoro-2,4,6-tri-
methylpyridinium triflate-water,10 photosensitized oxygena-
tion reactions,11 trichloroisocyanuric acid,12 and SiO2Cl/
DMSO.13
1. The preparation of NIBTS is easy.
2. NIBTS is stable for six months under atmospheric
conditions.
3. After reaction of NIBTS with substrate, the sul-
phonamide is recovered and can be reused many times with-
out decreasing the yield.
However, the above reaction did not proceed in the ab-
sence of silver nitrate; therefore it was decided to study the
application of NIBTS in the presence of silver nitrate. This
increase in reactivity may be due to a change in the electro-
philic iodine species caused by the presence of silver ion.5
The following mechanism for the reaction (Scheme II) is sug-
gested.
The results of the conversion of various 1,3-dithianes to
aldehydes and ketones are presented in Table 1.
Since NIBTS contain two iodine atoms which are at-
tached to nitrogen atoms, it is very possible that this reagent
releases I+ in situ in the presence of silver ion which can act as
RESULTS AND DISCUSSION
These oxidizing agents are relatively expensive; they
need high temperatures,9 photolyzation7,11 and are difficult to
prepare. On the other hand, there are numerous oxidative
methods using readily available cheap reagents and mild
conditions such as the most popular mercury(II) methods.1
Therefore it was decided to use a new reagent [NIBTS] 1,14
which is relatively easy to make from N,N¢-1,2-ethanediyl-
bis(p-toluenesulphonamide). We now report a convenient
method for conversion of 1,3-dithianes to aldehydes and ke-
tones using NIBTS/AgNO3 (Fig. 1).
I
N
CH2
S
)
2
O
O
NIBTS 1
Fig. 1.
* Corresponding author. Fax: +98-811-8272404; E-mail: ghorbani@basu.ac.ir

328 J. Chin. Chem. Soc., Vol. 52, No. 2, 2005
Ghorbani-Vaghei and Zolfigol
Scheme I
( )
n
O
C
NIBTS/AgNO
3
H
S
S
80% aq. CH CN, rt
3
+
N
C
R2
CH
)
1
1
R
R2
R
S
2
2
O
O
2
R1
alkyl, aryl, H
=
, R
n=1, 2
2
Scheme II
CH3
CH3
I
AgNO3
CH2
O
S
N
+
)
2
I
O
CH2
O
S
N
)
2
O
Ag
CH3
SO2
CH3
O2N OI
+
I
CH2
N
Ag+
)
O
CH2
S
N
NO3
)
2
2
O
Ag
( )
n
S
S
C
1
R
2
R
( )
n
( )
n
O
S
S
I
S
S
I
H2O
+
C
C
C
1
R
R2
OH2
R2
1
R
1
R
R2
H
+
N
AgNO3
CH
S
)
2
2
O
O
2

Mild Deprotection of 1,3-Dithianes
J. Chin. Chem. Soc., Vol. 52, No. 2, 2005 329
Table 1. Deprotection of 1,3-dithianes with NIBTS and AgNO3 in aq. acetonitrile at room
temperature
Entry
1
Substrate
Producta
Time
(min)
Yield
(%)
S
S
o
15
90
S
S
CH3
CHO
CH3
Ph
2
3
4
5
20
25
30
35
85
82
86
80
S
o
Ph
Ph
S
S
S
CHO
Ph
Ph
S
S
CHO
Ph
O
S
6
20
86
S
CH3
CH3
a Products were characterized by their physical properties, comparison with authentic samples, and by
spectroscopic methods.
an electrophilic species.14 The products of reaction with
dium carbonate and water and then was dried with MgSO4
and evaporated to give the product. Further purification was
achieved by chromatography on silica-gel column (eluent:
hexane) to give pure carbonyl compounds.
NIBTS were isolated simply by filtering off the sulfonamide
2 and evaporating the solvent from the filtrate. The method
has advantages in terms of yields, simplicity of reaction con-
ditions, short reaction times and lack of side products. The re-
covered starting material 2, was reiodinated and used many
times without reducing the yield.
Received August 27, 2004.
EXPERIMENTAL
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General procedure for deprotection of 1,3-dithianes us-
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A solution of the dithiane (1.0 mmol) in acetonitrile (2
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