Facile and efficient method for deprotection of 1,3-oxathiolanes with N,N′-dibromo-N,N′-1,2-ethanediylbis(p-toluenesulphonamide)

Article abstract of DOI:10.1080/10426500490466508

Aliphatic and aromatic 1,3-oxathiolanes are readily oxidized to aldehydes and ketones in good yields under mild conditions by N,N′-dibromo-N, N′-1,2-ethanediylbis(p-toluenesulphonamide) [BNBTS].

Full text of DOI:10.1080/10426500490466508

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Phosphorus, Sulfur, and Silicon and the Related
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FACILE AND EFFICIENT METHOD FOR DEPROTECTION
OF 1,3-OXATHIOLANES WITH N,N′-DIBROMO-N,N′-1,2-
ETHANEDIYLBIS(p-TOLUENESULPHONAMIDE)
Ramin Ghorbani-Vaghei a & Ardeshir Khazaei
a Department of Chemistry, Faculty of Science, Bu-Ali Sina University , Hamadan, Iran
Published online: 16 Aug 2010.
To cite this article: Ramin Ghorbani-Vaghei & Ardeshir Khazaei (2004) FACILE AND EFFICIENT METHOD FOR DEPROTECTION OF
1,3-OXATHIOLANES WITH N,N′-DIBROMO-N,N′-1,2-ETHANEDIYLBIS(p-TOLUENESULPHONAMIDE), Phosphorus, Sulfur, and Silicon
and the Related Elements, 179:9, 1787-1791, DOI: 10.1080/10426500490466508
To link to this article: http://dx.doi.org/10.1080/10426500490466508
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Phosphorus, Sulfur, and Silicon, 179:1787–1791, 2004
ꢀC
Copyright Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500490466508
FACILE AND EFFICIENT METHOD FOR
DEPROTECTION OF 1,3-OXATHIOLANES WITH
N,Nꢀ-DIBROMO-N,Nꢀ-1,2-ETHANEDIYLBIS(P-
TOLUENESULPHONAMIDE)
Ramin Ghorbani-Vaghei and Ardeshir Khazaei
Department of Chemistry, Faculty of Science, Bu-Ali Sina
University, Hamadan, Iran
(Received January 6, 2004; accepted January 8, 2004)
Aliphatic and aromatic 1,3-oxathiolanes are readily oxidized to aldehy-
des and ketones in good yields under mild conditions by N,Nꢁ-dibromo-
N,Nꢁ-1,2-ethanediylbis(p-toluenesulphonamide) [BNBTS].
Keywords: BNBTS; deprotection; oxathiolanes; oxidation
INTRODUCTION
The electrophilic nature of the carbonyl groups is a dominant feature
of their extensive chemistry. One of the major challenging problems
during many multistep syntheses is how to protect a carbonyl from nu-
cleophilic attack until its electrophilic properties can be exploited. For
this reason, deprotection of the carbonyl groups remains a crucial chal-
lenge to organic chemists. Among various functional groups, protection
of the carbonyl groups as a 1,3-oxathiolane is important for the fol-
lowing reasons: they can be used as acyl carbanion equivalents1a,b,c
for C C bond formation; the chiral 1,3-oxathiolanes are valuable
for synthesis of α-hydroxyaldehydes;1a and 1,3-oxathiolanes are com-
paratively more stable than O,O-acetals in acidic conditions, and
much easier to remove than S,S-acetals and as protecting groups of
carbonyl compounds.2 A variety of methods for the deprotection of
oxathiolanes are reported employing isoamylnitrite,3 chloramine-
T,4 TMSOTf alone5 or in the presence of p-nitrobenzaldehyde,6
polymer-supported p-nitrobenzaldehyde,7 NCS-AgNO3,8 I2-AgNO3,9
Address correspondence to Ramin Ghorbani-Vaghei, Department of Chemistry, Fac-
ulty of Science, Bu-Ali Sina University, Hamadan, Iran. E-mail: ghorbani@basu.ac.ir
1787

1788
R. Ghorbani-Vaghei and A. Khazaei
NBS in acetone,10 glyoxylic acid in the presence of Amberlyst 15 in a mi-
crowave oven11 and ammonium tribromide.12 However, these methods
suffer from drawbacks such as the difficulty of removing the byproduct
oxathioacetals derived from p-nitrobenzaldehyde,6 the use of expen-
sive polymer-supported reagent,7 on the requirement of a large mo-
lar excess of reagents such as expensive silver salts.8,9 Consequently,
it seems that there is still a need for development of newer methods
that can proceed under mild and economically appropriate conditions.
Therefore, we decided to study the application of N,Nꢁ-dibromo-N,Nꢁ-
1,2-ethanediylbis(p-toluenesulphonamide) [BNBTS],13 which is rela-
tively easy to make.
RESULTS AND DISCUSSION
We now report a convenient method for conversion of 1,3-oxathiolanes
to aldehydes and ketones using BNBTS (Figure 1).
Aliphatic and aromatic 1,3-oxathiolanes were found to be oxidized to
aldehydes and ketones using BNBTS in aqueous acetonitrile at room
temperature (Scheme 1).
SCHEME 1
FIGURE 1 Since BNBTS contain two bromine atoms that are attached to
nitrogen atoms it is very possible that this reagent releases Br+ which can act
as an electrophilic species,13 in situ.

Deprotection of Oxathiolanes
1789
The advantages of BNBTS are as follows:
1. The preparation of BNBTS is easy.
2. BNBTS is stable in atmospheric conditions for two months.
3. After completion of the reaction and evaporation of solvent, the
sulphonamide is recovered and can be reused many times without
decreasing the yield.
The results of the conversion of various 1,3-oxathiolanes to aldehydes
and ketones are presented in Table I.
Since BNBTS contains two bromine atoms that are attached to ni-
trogen atoms, it is very possible that this reagent releases Br+ which
can act as an electrophilic species,13 in situ. The products of reaction
TABLE I Deprotection of 1,3-Oxathiolanes with BNBTS in Aqueous
Acetonitrile at Room Temperature
Time
[min]/h
Entry
1
Substrate
Producta
Yield (%)
90
4
2
3
[30]
2.5
93
84
4
5
[60]
[90]
89
92
6
7
8
[20]
7
82
85
90
10
aProducts were characterized by their physical properties, comparison with authentic
samples, and by spectroscopic methods.

1790
R. Ghorbani-Vaghei and A. Khazaei
with BNBTS were isolated simply by filtering off the sulfonamide 2
and evaporating the solvent from the filtrate. The method has advan-
tages in terms of yields, simplicity of reaction conditions, short reaction
times, and lack of side products. The recovered starting material 2 was
rebrominated and used many times without reducing the yield.
CONCLUSION
From the results obtained, we find that the described procedure and
the reaction conditions are simple. The new reagent (BNBTS) is stable
and the recovered reagent can be reused.
Infrared (IR) and nuclear magnetic resonance (NMR) spectra were
recorded using a Shimadzu 435-U-04 spectrophotometer (KBr pellets)
and a 90 MHz Jeol FT-NMR spectrometer, respectively.
GENERAL PROCEDURE FOR DEPROTECTION
OF 1,3-OXATHIOLANES USING BNBTS
A solution of the 1,3-oxathiolane (1.0 mmol) in acetonitrile (2 ml) was
added quickly to a well-stirred solution of BNBTS (4 mmol) in aqueous
80% acetonitrile (10 ml) at room temperature. The mixture was stirred
for the specified time (Table I). After completion of the reaction, the
insoluble sulphonamide 2 was removed by filteration and washed with
cold acetonitrile (5 ml). The solvent was then evaporated and ether was
added. The ethereal phase was washed with saturated aqueous sodium
carbonate and water and then was dried with MgSO4 and evaporated
to give the product.
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