1,3-Dibromo-5,5-dimethylhydantoin or N-bromosuccinimide as efficient reagents for chemoselective deprotection of 1,1-diacetates under solvent-free conditions

Article abstract of DOI:10.1007/s00706-009-0212-9

A simple and efficient method is reported for rapid chemoselective transformation of 1,1-diacetates to the parent aldehydes using 1,3-dibromo-5,5-dimethylhydantoin or N-bromosuccinimide in the presence of wet SiO₂ (50%, w/w) as solid support under solvent-free conditions at room temperature. This procedure has valuable advantages, for example short reaction times, simple work-up, high yields of products, absence of solvent, and use of commercially available and non-toxic reagents.

Full text of DOI:10.1007/s00706-009-0212-9

Monatsh Chem (2009) 140:1485–1488
DOI 10.1007/s00706-009-0212-9
ORIGINAL PAPER
1,3-Dibromo-5,5-dimethylhydantoin or N-bromosuccinimide
as efficient reagents for chemoselective deprotection
of 1,1-diacetates under solvent-free conditions
•
Behrooz Maleki Davood Azarifar Ramin Ghorbani-vaghei
•
•
•
•
•
•
Hojat Veisi Seyedeh Fatemeh Hojati Mostafa Gholizadeh Hafezeh Salehabadi
Mona Khodaverdian Moghadam
Received: 23 February 2009 / Accepted: 13 October 2009 / Published online: 7 November 2009
Ó Springer-Verlag 2009
Abstract A simple and efficient method is reported for
rapid chemoselective transformation of 1,1-diacetates to
the parent aldehydes using 1,3-dibromo-5,5-dimethylhy-
dantoin or N-bromosuccinimide in the presence of wet
SiO2 (50%, w/w) as solid support under solvent-free con-
ditions at room temperature. This procedure has valuable
advantages, for example short reaction times, simple work-
up, high yields of products, absence of solvent, and use of
commercially available and non-toxic reagents.
chemistry [1, 2]. Among the different functional groups,
carbonyl groups have attracted special attention in protec-
tion and deprotection reactions by virtue of their high
reactivity. One useful practice for protection of carbonyl
groups is 1,1-diacetylization, which has received consid-
erable interest in recent years, because 1,1-diacetates are
stable in mildly acidic and basic media and are easily pre-
pared [3–10]. However, the search for appropriate
and efficient methods for deprotection of 1,1-diacetates to
the corresponding carbonyl compounds is still in high
demand. In this regard, much effort has been devoted
to developing numerous methodologies using various
reagents such as phosphorus trichloride [11], boron triio-
dide–N,N-diethylaniline complex [12], mineral solid
supports [13], MoO2(acac)2 [14], FeCl3Á6H2O [15],
graphite [16], CuCl2Á2H2O [17], zirconium sulfophenyl
phosphonate [18], ceric ammonium nitrate (CAN) [19],
indium trichloride [20], [NO?. crown. H (NO3)2-]
[21], Caro’s acid/SiO2 [22], H6P2W18O62Á24H2O [23],
Fe2(SO4)3ÁxH2O [24], 12-molybdophoshoric acid [25],
p-toluene sulfonic acid [26], SO42-/SnO2 [27], molybde-
num tungsten polyoxometalates [28], KBrO3/MoO3
[29], (NH4)3PW12O40 [30], dodecatungstophosphoric acid
(H3PW12O40) [31], sodium hydrogen sulfate in poly(eth-
ylene glycol) [32], indium tribromide/[bmim]PF6 [33],
indium tribromide in poly(ethylene glycol) [34], 2,6-dica-
rboxypyridinium chlorochromate [35], and ZrOCl2 [36].
Although many of these procedures have been satisfactorily
used for this propose, most suffer from one or more draw-
backs, for example low yields, harsh reaction conditions,
difficult work-up, and use of expensive and/or toxic
reagents and solvents. In view of these limitations and also
with regard to yields, reaction time, toxicity, and catalytic
loading, our method is believed to be superior to those
previously reported.
Keywords 1,1-Diacetates Á Aldehydes Á Wet silica gel Á
1,3-Dibromo-5,5-dimethylhydantoin Á
N-Bromosuccinimide Á Solvent-free conditions
Introduction
Protection and deprotection of functional groups are
important and extensively used transformations in synthetic
B. Maleki (&) Á S. F. Hojati Á M. Gholizadeh Á
H. Salehabadi Á M. K. Moghadam
Department of Chemistry,
Sabzevar Tarbiat Moallem University,
Sabzevar, Iran
e-mail: malekibehrooz@gmail.com
D. Azarifar Á R. Ghorbani-vaghei
Department of Chemistry,
Bu-Ali Sina University,
Hamadan, Iran
H. Veisi
Department of Chemistry,
Payame Noor University, Songhor,
Kermanshah, Iran
123

1486
B. Maleki et al.
Results and discussion
Table 1 Conversion of 1,1-diacetates 1a–1m to aldehydes 2a–2m
catalyzed by wet SiO2-supported DBH
Recently, 1,3-dibromo-5,5-dimethylhydantoin (DBH) and
N-bromosuccinimide (NBS) have gained much attention as
oxidation and bromination agents in organic reactions [37–
39]. These compounds are relatively non-toxic, commer-
cially available, inexpensive, and stable to air and
moisture. In this work we examined the catalytic ability of
DBH and NBS in the solvent-free deprotection of 1,1-
diacetates to the corresponding aldehydes using wet SiO2
as a solid support. To achieve this, 1,1-diacetates 1a–1m
were reacted with DBH or NBS in different molar ratios
with or without use of wet SiO2 to yield the corresponding
aldehydes 2a–2m (Scheme 1). According to the experi-
mental data reported in Tables 1 and 2, the best results
were obtained when the reactions were carried out using
wet SiO2. It is found that both aromatic and aliphatic 1,1-
diacetates were efficiently converted to their parent alde-
hydes with DBH and NBS, respectively, in 72–96% and
68–94% yields (Tables 1, 2) under mild reaction condi-
tions. It is important to note that no conversion of the 1,1-
diacetates to aldehydes was observed when the reactions
were carried out in the absence of either of these reagents.
Synthetically, chemoselectivity in chemistry is regarded
as one of the most important aspects of organic reactions.
In this regard, the selectivity of this method was investi-
gated by conducting a competitive reaction on a 1:1
mixture of 1,1-diacetates derived from benzaldehyde and
Entry
R
Aldehyde Catalysta Time Yield
(min) (%)b,c
1
C6H5
2a
2b
2c
2d
2e
2f
2.5
3
3
5
4
4
5
5
4
4
4
2
3
4
4
84
90
96
84
72
90
74
80
84
75
84
90
86
2
2-ClC6H4
4-ClC6H4
2-CH3C6H4
4-CH3C6H4
2-HOC6H4
4-CNC6H4
2-NO2C6H4
3
2.5
2.5
2.5
2.5
3
4
5
6
7
2g
2h
8
3.25
3
9
3-CH3O-2-NO2C6H4 2i
10
11
12
13
a
C6H5CH=CH
CH3CH2
2j
2
2k
2l
2.25
2.25
2.25
CH3(CH2)2
(CH3)2CH
2m
Amount of catalyst used for 1 mmol of substrate
Products were characterized by physical and spectral (1H, 13C
b
NMR, and IR) analysis and the results were compared with data
reported in the literature
c
Isolated yields
Table 2 Conversion of 1,1-diacetates 1a–1m to aldehydes 2a–2m
catalyzed by wet SiO2-supported NBS
Entry
R
Aldehyde Catalysta Time Yield
(min) (%)b,c
1
acetophenone (Scheme 2). As the H NMR spectral anal-
ysis indicated, only the benzaldehyde diacetate was
chemoselectively converted to benzaldehyde whereas the
acetophenone diacetate remained intact under the same
reaction condition. As a result, this procedure can be
regarded as potentially useful for chemoselective depro-
tection of aldehyde diacetates in the presence of ketone
diacetates.
1
C6H5
2a
2b
2c
2d
2e
2f
3
4
5
6
6
6
5
5
4
4
3
3
4
6
92
90
90
80
70
81
68
79
87
80
87
94
80
2
2-ClC6H4
4-ClC6H4
2-CH3C6H4
4-CH3C6H4
2-HOC6H4
4-CNC6H4
2-NO2C6H4
3.5
3.5
4
3
4
5
4
6
2.5
3.25
4
7
2g
2h
Although the mechanism of this reaction is not yet fully
understood, one possibility is suggested in Scheme 3. It is
based on:
8
9
3-CH3O-2-NO2C6H4 2i
4
10
11
12
13
a
C6H5CH=CH
CH3CH2
2j
3
1
2
reduction of reaction rates when dry SiO2 is used; and
the similar reactivities of aromatic and aliphatic
aldehyde diacetates in these reactions.
2k
2l
2.25
2.5
3.5
CH3(CH2)2
(CH3)2CH
2m
As shown in this mechanism, possible in-situ release of
Amount of catalyst used for 1 mmol of substrate
Products were characterized by physical and spectral (1H, 13C
b
bromide ion by DBH and NBS occurs [40, 41], and this ion
NMR, and IR) analysis and the results were compared with data
reported in the literature
c
Isolated yields
OAc
DBH or NBS/Wet SiO2
R
CH
R
CHO
Solvent-Free, rt
subsequently attacks one of the oxygen atoms in the acetate
to promote the hydrolysis step.
OAc
1a-1m
2a-2m
In conclusion, we have developed a rapid, selec-
tive, simple, and efficient procedure for deprotection of
Scheme 1
123

1,3-Dibromo-5,5-dimethylhydantoin or N-bromosuccinimide as efficient reagents
1487
Scheme 2
OAc
C
OAc
Wet SiO2
4 min, rt
+
OAc
CHO +
COCH3
CH
OAc
CH3
DBH (2.5 mmol) 84%
NBS (3 mmol) 92%
0%
0%
Br
Br
O
Br
O
O
R
OAc
OAc
R
H
DBH
or
NBS
R
H
R
C
R
AcOH (H+)
-AcOH
Wet SiO2 (H2O)
-AcOH
C
+
C
Br
C
O
C
OAc
O-Ac
H
OAc
H
H
H
-Br+
1a-1m
RCHO
2a-2m
Scheme 3
for financial support to carry out this research. We also thank Mrs
Neda Rahiminezhad for her assistance.
1,1-diacetates derived from aldehydes. This reaction
proceeds rapidly at room temperature to afford the
product in excellent yield with no side product formation.
Short reaction times, high yields, mild conditions, easy
workup, absence of the solvent in the reaction, and the
use of non-toxic, commercially available, and inexpen-
sive reagents are the main advantages of this method
that make it environmentally friendly and industrially
applicable.
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