Poly(N-bromobenzene-1,3-disulfonamide) and N,N,N′,N′- tetrabromobenzene-1,3-disulfonamide as a mild and efficient catalyst for chemoselective thioacetalization of carbonyl functions and transthioacetalization reactions

Article abstract of DOI:10.1002/jhet.620

Poly(N-bromobenzene-1,3-disulfonamide) and N,N,N′,N′- tetrabromobenzene-1,3-disulfonamide are effective catalysts for chemoselective dithioacetalization of aldehydes in the presence of ketones under neutral conditions.

Full text of DOI:10.1002/jhet.620

May 2011
Poly(N-Bromobenzene-1,3-disulfonamide) and N,N,N0,N0-
Tetrabromobenzene-1,3-disulfonamide as a Mild and Efficient
Catalyst for Chemoselective Thioacetalization of Carbonyl
Functions and Transthioacetalization Reactions
699
Hojat Veisi,a* Ramin Ghorbani-Vaghei,b and Somayeh Akbari Dadamahalehb
aDepartment of Chemistry, Payame Noor University (PNU), Iran
bDepartment of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University, Hamedan, Iran
*E-mail: hojatveisi@yahoo.com
Received May 27, 2010
DOI 10.1002/jhet.620
Published online 22 February 2011 in Wiley Online Library (wileyonlinelibrary.com).
Poly(N-bromobenzene-1,3-disulfonamide) and N,N,N0,N0-tetrabromobenzene-1,3-disulfonamide are
effective catalysts for chemoselective dithioacetalization of aldehydes in the presence of ketones under
neutral conditions.
J. Heterocyclic Chem., 48, 699 (2011).
INTRODUCTION
expensive reagents and/or chlorinated organic solvents,
harsh reaction conditions, difficulties in work-up, and in
some instances strong acidic reagents.
The protection of carbonyl functionality as a dithioa-
cetal [1] is important in the total synthesis of complex
natural and non-natural products [2]. Thioacetals are
quit stable toward a wide variety of reagents [3] and are
also useful in organic synthesis as acyl carbanion equiv-
alents [3] in CAC bond-forming reaction.
N-Halo compounds are versatile reagents and have
been employed as potentially reactive intermediates that
are widely used in organic synthesis. N-halo reagents
are easy to handle with all of the halogen being con-
sumed, and not half, as in the case of elemental halo-
gens. Some specific features of N-halo reagents such as
the high activity of the N-X bond and the various modes
of splitting of this bond determine their wide application
in organic synthesis [26,27].
Transthioacetalization of acetals and acylals has also
been used as an alternative method for the preparation
of thioacetals [4]. They are usually prepared by the con-
densation of carbonyl compounds with thiols or dithiols
using a strong protic acid such as HCl [5] or Lewis
acids such as BF3.OEt2 [6] or ZnCl2 [7] as catalysts.
Other Lewis acids viz. AlCl3 [8], LnCl3 [9], TiCl4 [10],
WCl6 [3], InCl3 [11], Sc(OTf)3 [12], Bi(NO3)3 [13],
VO(OTf)2 [14], CoCl2 [15], BiCl3 and Bi(SO4) [13],
SiCl4 [16], Al(HSO4) [17], P2O5/SiO2 [18], and
[bmim]HSO4 [19]. A number of milder procedures
employing lithium salts [20], NiCl2 [21], trichloroiso-
cyanoric acid [22], NBS [23], I2 [24], microwave [25],
and silica functionalized sulfonic acid [26] have also
been reported for this purpose. Unfortunately, many of
these protocols suffer from the drawbacks such as a
requirement for stoichiometric amounts of catalysts, low
yields of the products, long reaction times, the use of
RESULTS AND DISCUSSION
In this communication, we wish to report a mild and
highly chemoselective procedure for the conversion of
aldehydes in present of ketones into 1,3-dithiolanes and
1,3-dithianes using catalytic amount of poly(N-bromo-
benzene-1,3-disulfonamide) (PBBS) and N,N,N0,N0-tet-
rabromobenzene-1,3-disulfonamide (TBBDA) [28–35]
under almost neutral reaction conditions (Scheme 1).
First we carried out the reaction of benzaldehyde,
with 1,2-ethandithiol in presence of TBBDA (0.05
mmol) at room temperature using different solvents such
C
V
2011 HeteroCorporation

700
H. Veisi,, R. Ghorbani-Vaghei, and S. A. Dadamahaleh
Vol 48
Scheme 1
as CH2Cl2, CHCl3, CCl4, CH3CN, EtOH. The results
are listed in Table 1.
rate of ketones (Table 2) allows for chemoselective pro-
tection of acylal in the presence of ketone (Scheme 2).
Our preliminary examination shows that TBBDA or
PBBS are reusable catalytic reagents. Thus, after the
successful thioacetalization of p-chlorobenzaldehyde in
first run, which gave the corresponding product in 98%
isolated yield (Table 2, entry 7), the TBBDA catalyst
was subjected to a second thioacetalization reaction
from which it gave the product in 90% yield; the aver-
age chemical yield for five consecutive runs was 55%.
In this curve (Scheme 3), we show the repetition is
reduced gratuately. The data shows a good agreement
with the function of y ¼ ꢀ10.6xþ110.8 with a regres-
sion coefficient of R2 ¼ 0.978.
It shows that CH3CN is a better solvent (yield 96%)
than other solvents tested. In addition, we also studied
influence of the amount of TBBDA and PBBS on the
reaction yields. We found that the good yield is obtained
in 0.05 mmol of TBBDA and 0.1 g of PBBS. In the
light of this, subsequent studies were carried out under
the following optimized conditions, that is, with
TBBDA (0.05 mmol) and PBBS (0.1 g) at room temper-
ature in CH3CN.
As shown in Table 2, various types of aromatic alde-
hydes with electron-donating and electron-withdrawing
groups were cleanly and rapidly converted to the corre-
sponding dithianes and dithiolanes in the presence of
catalysts. However, aromatic and aliphatic ketones were
slowly converted to their corresponding S,S-acetals (Ta-
ble 2, entries 23–28). Transthioacetalization of O,O-ace-
tals, O,O-ketals and acylals was also achieved efficiently
with a catalytic amount of TBBDA and PBBS to afford
the corresponding S,S-acetals in high yields (Table 2,
entries 31–38).
To compare PBBS and TBBDA with previously pub-
lished methods for the thioacetalization of carbonyl
compounds with benzaldehyde, p-chlorobenzaldehyde
and p-methoxybenzaldehyde we carried out the follow-
ing studies, as shown in Table 3. This clearly demon-
strates that PBBS and TBBDA are good catalysts for
the thioacetalization of carbonyl compounds.
We observed that the reaction with aldehydes takes
place rapidly in the presence of TBBDA and PBBS
when compared with ketones (Table 2). The difference
in reactivity of the TBBDA and PBBS catalysts towards
aldehydes and ketones gave us impetus to study chemo-
selective reactions. Towards this objective, we carried
out initial experiments with equimolar mixtures of an
aldehyde and a ketone (Scheme 2). When an equimolar
(1 mmol) mixture of p-methoxybenzaldehyde and aceto-
phenone was allowed to react with 1.1 mmol of 1,2-
ethandithiol and catalytic amount of TBBDA and PBBS
in acetonitrile at room temperature, a high yield (97%)
of (II) was obtained and unchanged acetophenone was
recovered (Scheme 2). So, the relatively slow reaction
Table 1
Solvent effect on the reaction of benzaldehyde and 1,2-ethandithiol by
TBBDA in room temperature.a
Entry
Solvent
Time (min)
Yield (%)b
1
2
3
4
5
CH2C12
CHC13
CCl4
40
60
90
35
35
90
80
85
96
90
CH3CN
EtOH
a 0.05 mmol.
b Isolated yield.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

May 2011
Chemoselective Thioacetalization of Carbonyl Functions
701
Table 2
Thioacetalization of carbonyl compounds and transthioacetalization catalyzed by TBBDA and PBBS in CH3CN at ambient conditions.
TBBDA PBBS
Time(min)[h] Time (min)[h]
Entry
1
Substrate
Product
Yield (%)a
96
Yield (%)
(35)
(40)
92
2
(35)
90
(40)
90
3
4
(40)
(45)
92
90
(40)
(45)
90
88
5
6
(15)
(20)
97
97
(30)
(35)
95
92
7
8
(20)
(25)
98
98
(20)
(30)
98
96
9
[1]
95
90
[1.2]
[1.3]
92
86
10
[1.2]
11
12
(25)
(30)
94
90
(30)
(40)
94
90
13
(45)
90
(50)
85
(Continued)
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Table 2
(Continued)
TBBDA
PBBS
Time (min)[h]
Entry
14
Substrate
Product
Time(min)[h]
(55)
Yield (%)a
88
Yield (%)
82
[1.1]
15
16
(50)
(55)
90
90
[1]
88
85
[1.1]
17
I8
(5)
(5)
98
97
(5)
(5)
98
96
19
20
[1.6]
[2]
86
80
[2]
85
75
[2.5]
21
22
[1.3]
[1.5]
88
82
[1.5]
[1.7]
80
80
23
24
[7]
[8]
40
35
[7]
40
35
[8.5]
25
26
[4.5]
[5]
65
60
[5]
65
60
[5.2]
(Continued)

Table 2
(Continued)
TBBDA
PBBS
Time (min)[h]
Entry
27
Substrate
Product
Time(min)[h]
[4]
Yield (%)a
65
Yield (%)
65
[4.5]
28
[5]
62
[5]
60
29
30
[1.2]
[1.2]
92
90
[1.5]
[1.3]
90
89
31
32
[1.5]
[2]
92
86
[1.6]
[2]
90
85
33
34
[2]
90
87
[2]
90
86
[2.2]
[2.2]
35
36
37
[1.5]
[2]
92
90
75
[1.7]
[2.5]
[6.5]
85
88
75
[6]
38
[7]
70
[8]
70
a Products were characterized from their physical properties, comparison with authentic samples and by spectroscopic methods (lH NMR and IR).

704
H. Veisi,, R. Ghorbani-Vaghei, and S. A. Dadamahaleh
Vol 48
Scheme 2
(2 mL) was added 1,2-ethandithiol or 1,3-propandithiole (1.1
mmol) at room temperature. The mixture was stirred for an
appropriate time (Table 2). After completion of reaction as
indicated by TLC, the organic solvent was concentrated in
vacuum and then CH2Cl2 (10 mL) was added, and the catalyst
was removed by filtration. Evaporation of the solvent under
reduced pressure gave the products. Further purification was
achieved by recrystalization from ethanol (90%).
CONCLUSION
In summary, in this study we have introduced a new
and useful catalytic application of TBBDA and PBBS as
efficient catalysts for the thioacetalization of aldehydes,
O,O-acetals, O,O-ketals and acylals under mild reaction
conditions. The method is highly chemoselective for
protection of aldehydes in the presence of ketones.
Moreover, the method has advantages in terms of high
yields of products, short reaction times, operational sim-
plicity and easy work up of products.
Table 3
Reaction times and yield for previously published methods.
Reaction Yield
time (min) (%)
Substrate
Conditions
EXPERIMENTAL
Benzaldehyde
NBS, 1,2 propandithiol,
CH2C12, rt
NiCl2, 1,2 propandithiol,
CH2CI2- MeOH, rt
CoCl2, 1,2 propandithiol,
CH3CN, rt
Trichloroisocyanoric
acid, 1,2 propandithiol,
CHCl3, rt
40
165
300
60
8023
9621
8915
9522
General procedure for thioacetalization and transthioa-
cetalization of acetals and acylals catalyzed by TBBDA and
PBBS in CH3CN. To a stirred solution of substrate 1–18
(1mmol) and TBBDA (0.05 mmol) or PBBS (0.1 g) in CH3CN
Benzaldehyde
Benzaldehyde
Benzaldehyde
p-(Cl)-
benzaldehyde
p-(Cl)-
benzaldehyde
p-(Cl)-
benzaldehyde
p-(Cl)-
benzaldehyde
CoCl2,1,3 propandithiol,
CH3CN, rt
NBS, 1,3 propandithiol,
CH2C12, rt
Sc(OTf)3, 1,3 propandi-
thiol, CH2C12, rt
Trichloroisocyanoric
acid, 1,2 propandithiol,
CHC13, rt
30
30
8815
7823
9012
9422
Scheme 3
40
120
p-(MeO)-
benzaldehyde
p- (MeO)-
benzaldehyde
p-(MeO)-
benzaldehyde
NBS, 1,3 propandithiol,
CH2Cl2 rt
NiCl2, 1,3 propandithiol,
CH2C12-MeOH, rt
CoCl2 1,3 propandithiol,
CH3CN, rt
30
75
30
7023
8921
9215
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

May 2011
Chemoselective Thioacetalization of Carbonyl Functions
705
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet