New application of cross-linked poly(N -bromoacrylamide) and poly(N -bromosuccinimide) as highly efficient and chemoselective heterogeneous polymeric catalysts for deprotection of 1,3-dithianes and 1,3-dithiolanes under mild conditions

Article abstract of DOI:10.1080/17415993.2015.1094805

Cross-linked poly(N-bromoacrylamide) (PNBA) and poly(N- bromosuccinimide) as the mild and efficient heterogeneous polymeric catalysts were applied for selective deprotection of 1,3-dithianes and 1,3-dithiolanes to their corresponding carbonyl compounds. They were also effective as a reagent in aqueous media. These methods are very simple and the polymer catalysts could be recycled several times. Deprotection of thioacetal and thioketal without enolizable hydrogens proceeded very well to give only the corresponding aldehyde and ketone in high to excellent yield. Nevertheless, in the case of thioketals carrying enolizable hydrogens, deprotection accompanied with the formation of a minor ring-expanded product is observed. However, using the PNBA/H₂O system, ring expansion of these thiolketals with enolizable hydrogen was not detected. These methods provide advantages, such as chemoselectivity, easy preparation, simple work up, excellent yields, and the ability to recycle the catalyst, which makes this method more useful compared to other known methodologies.

Full text of DOI:10.1080/17415993.2015.1094805

Journal of Sulfur Chemistry
ISSN: 1741-5993 (Print) 1741-6000 (Online) Journal homepage: http://www.tandfonline.com/loi/gsrp20
New application of cross-linked poly(N-
bromoacrylamide) and poly(N-bromosuccinimide)
as highly efficient and chemoselective
heterogeneous polymeric catalysts for
deprotection of 1,3-dithianes and 1,3-dithiolanes
under mild conditions
Farzaneh Ebrahimzadeh
To cite this article: Farzaneh Ebrahimzadeh (2015): New application of cross-linked poly(N-
bromoacrylamide) and poly(N-bromosuccinimide) as highly efficient and chemoselective
heterogeneous polymeric catalysts for deprotection of 1,3-dithianes and 1,3-dithiolanes under
mild conditions, Journal of Sulfur Chemistry, DOI: 10.1080/17415993.2015.1094805
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Date: 28 November 2015, At: 23:37

JOURNAL OF SULFUR CHEMISTRY, 2015
http://dx.doi.org/10.1080/17415993.2015.1094805
New application of cross-linked poly(N-bromoacrylamide)
and poly(N-bromosuccinimide) as highly efficient and
chemoselective heterogeneous polymeric catalysts for
deprotection of 1,3-dithianes and 1,3-dithiolanes under mild
conditions
Farzaneh Ebrahimzadeh
Department of Chemistry, Marvdasht Branch, Islamic Azad University, Marvdasht, Iran
ABSTRACT
ARTICLE HISTORY
Cross-linked poly(N-bromoacrylamide) (PNBA) and poly(N- bromo-
succinimide) as the mild and efficient heterogeneous polymeric cat-
alysts were applied for selective deprotection of 1,3-dithianes and
Received 20 June 2015
Accepted 12 September 2015
KEYWORDS
1,3-dithiolanes to their corresponding carbonyl compounds. They
1,3-dithiane; 1,3-dithiolane;
were also effective as a reagent in aqueous media. These meth-
ods are very simple and the polymer catalysts could be recycled
several times. Deprotection of thioacetal and thioketal without eno-
lizable hydrogens proceeded very well to give only the correspond-
ing aldehyde and ketone in high to excellent yield. Nevertheless, in
the case of thioketals carrying enolizable hydrogens, deprotection
accompanied with the formation of a minor ring-expanded product
is observed. However, using the PNBA/H2O system, ring expansion of
these thiolketals with enolizable hydrogen was not detected. These
methods provide advantages, such as chemoselectivity, easy prepa-
ration, simple work up, excellent yields, and the ability to recycle the
catalyst, which makes this method more useful compared to other
known methodologies.
poly(N-bromoacrylamide);
poly(N-bromosuccinimide);
chemoselective
deprotection; carbonyl
compounds; heterogeneous
catalyst
Introduction
Thioacetals andthioketals are recognized as excellent protecting groups for car-
bonyl groups and are widely used in synthetic organic chemistry. They tolerate
CONTACT Farzaneh Ebrahimzadeh
polychemfar@gmail.com
©
2015 Taylor & Francis

2
F. EBRAHIMZADEH
both neutral and basic conditions.[1] Their deprotection to carbonyl groups, espe-
cially under mild reaction condition, is considered an important transformation in
organic synthesis.[2] A large number of methods have been employed using hetero-
geneous catalysts for cleavage of thioacetal to their parent carbonyl compounds. Het-
erogeneous catalysts such as natural kaolinitic clay,[3] Clayfen (MW or Hexan),[4]
Clayan (MW or CH Cl ),[5,6] wet montmorillonite K-10 Clay,[7] selectfuor,[8]
2
2
SiO /Cu(NO ) ,[9] silica sulfuric acid/NaNO ,[10] Copper salts,[11] SiO /Fe(NO ) ,[12]
2
3 2
3
2
3 3
silica chloride (dry DMSO),[13] Amberlyst,[14] Dowex,[15] tungstate sulfuric acid,[16]
Hg(NO ) ·3H O,[17] and Zr(CH PO ) (O PC H SO H) [18] as a heterogeneous cat-
3
2
2
3
3 12
3
6
4
3
0.8
alyst have been used for these transformations. However, many of these methods suffer
from one or more of the following disadvantages: long reaction times, vigorous reac-
tion conditions, the occurrence of side reactions, unavailability of the reagents, and
poor yields of the desired product. Furthermore, the abovementioned protocols usually
involve organic solvents. Therefore, the introduction of a new simple mild method for the
deprotection of thioacetals and ketals is still worthwhile.
Recently, new oxidative methods using a source of electrophilic halogens such as
ꢀ
NBS, TABCO and Br ,t-BuOCl,[19–21] N,N -2,4,6-trichloro-1,3,5-triazine,[22] dibromo-
2
ꢀ
N,N -1,2-ethanediyl bis(p-toluenesulfonamide),[23,24] Oxone/KBr,[25] o-Iodoxybenzoic
acid,[26,27] H O /I ,[28] H O /HBr,[29,30] H O –SOCl ,[31] and N,N,N ,N - tetrabro-
ꢀ
ꢀ
2
2
2
2
2
2
2
2
mobenzene-1,3-disulfonamide[32] have been reported for deprotection of dithiane and
dithiolane compounds in the presence of oxygen transfer agents such as DMSO or H O. In
2
addition, some sources of electrophilic halogens such as TABCO, NBS, t-BuOCl,[19–21]
and I [28] in the presence of DMSO can act as a catalyst for deprotection of thioac-
2
etals. It has also been reported that compounds such as NBS/AgNO , NCS/AgNO ,[33]
3
3
Br , Cl ,[19–21] and Oxone/KBr[23,24] can act as electrophilic halogen reagents for
2
2
deprotection of thioacetal under aqueous conditions.
To the best of our knowledge, there has been no report in the literature about the
use of heterogeneous polymeric sources of electrophilic halogen for the deprotection of
thioacetals and thioketals. So, we decided to explore the efficacy of different cross-linked
polymers and oxidants (water or DMSO) for the deprotection of thioacetals.
In this paper, we present new applications of cross-linked poly(N-bromoacrylamide)
(
PNBA) and poly(N-bromosuccinimide) (PNBS) as heterogeneous sources of electrophilic
bromine for the deprotection of 1,3-dithiane and 1,3-dithiolane under two different con-
ditions. In a system in which DMSO is applied as an oxidant, PNBA or PNBS is used
catalytically. However, when the reactions are performed in water, PNBA or PNBS would
be employed as a reagent.
Results and discussion
Cross-linked polyacrylamide (5% DVB) was prepared according to our previous
procedure,[34–36] which was further brominated using an Oxone/KBr system to provide
PNBA. This method is a very simple and green procedure using an aqueous solution of
Oxone and does not require organic solvents. The capacity of PNBA was determined by an
iodometric method to be 5.6 mmol of electrophilic bromine per gram of polyacrylamide.
Cross-linked PNBS (7% DVB) with the capacity 6.4 mmol of electrophilic bromine per

JOURNAL OF SULFUR CHEMISTRY
3
Table 1. Conversion of 2-phenyl-1,3-dithiolane to benzaldehyde with various molar ratios of PNBA or
a
PNBS in the presence of DMSO at room temperature.
Entry
Polymer (mmol)
PNBA time
PNBA conversion (%)
PNBS time
PNBS conversion (%)
1
2
3
4
5
6
7
8
a
1
5 min
5 min
10 min
15 min
20 min
35 min
12 h
100
100
100
100
100
100
75
immediately
immediately
immediately
immediately
5 min
15 min
20 min
1 h
100
100
100
100
100
100
100
0.8
0.6
0.4
0.3
0.2
0.1
0.2
b
b
3 h
100
100
The molar ratio of DMSO/2-phenyl-1,3-dithiane is 3/1.
CH2Cl2 was applied as a solvent.
b
Table 2. Conversion of 2-phenyl-1,3-dithiolane (1.0 mmol) to benzaldehyde with various molar ratios of
a
PNBA or PNBS in the presence of H2O at room temperature.
Entry
Polymer (mmol)
PNBA time
PNBA conversion (%)
PNBS time
PNBS conversion (%)
1
2
3
4
5
6
7
5
3
2
1
0.8
0.5
0.2
70 min
1 h
1 h
100
100
100
100
70
50 min
70 min
1.5 h
4 h
24 h
24 h
90
90
90
75
60
40
10
4 h
24 h
24 h
24 h
45
20
24 h
aExcess of water.
gram of PNBS was also prepared according to our previous procedure by using Br /CCl4
2
as the brominating agent.[37]
As a model reaction, phenyl-l,3-dithiane was deprotected to form benzaldehyde using
PNBA in different molar ratios combined with a three-fold excess of DMSO (Table 1) or
water (Table 2). As it can be observed in Table 1, in the presence of DMSO, the decrease in
the molar ratio of PNBS did not have an effect on the reaction yield (Table 1, Entries 2–6);
even when 0.2 molar ratio of the polymer was applied the reaction proceeded to completion
in a satisfactory time (Table 1, Entry 6). Consequently, in the presence of DMSO, PNBS
would act as a catalyst. Besides, when the reaction was carried out in a solvent such as
CH Cl , the deprotection time was increased (Table 1, Entry 8). Similar results were also
2
2
obtained using PNBA as a catalyst in the presence of DMSO. However, a lesser molar ratio
of the PNBS (0.1 mmol for 1 mmol substrate) as a catalyst would result in a faster reaction
rather than PNBA (Table 1, Entry 7). On the other hand, in the absence of DMSO, when
catalytic amounts of PNBS were applied, dethioacetalization of the model compound was
sluggish, and poor yield of the corresponding aldehyde was obtained after a long period of
time (Table 2, Entry 7).
However, when water is used as a solvent and as an oxygen transfer agent, PNBA and
PNBS act as a reagent. Herein, when one or two molar excesses of the polymers are applied,
the reaction proceeds to completion at a reasonable rate (Table 2, Entries 2 and 3), whereas
the polymers are consumed completely as a reagent, but would be regenerated and reused
again. The scope and generality of these dethioacetalization reactions were examined by
deprotection of several different 1,3-dithiolanes and 1,3-dithianes under both conditions
and in the presence of both polymers (Scheme 1, Tables 3 and 4).

4
F. EBRAHIMZADEH
Scheme 1. Deprotection of several different 1,3-dithiolanes and 1,3-dithianes under PNB(A or S)/DMSO
and PNB(A or S)/H2O conditions.
These methods are applicable to acyclic and cyclic thioacetals and thioketals of aro-
matic, heterocyclic, and aliphatic systems. Various types of both open-chain and cyclic
dithioacetals of several of aldehydes as well as cinamaldehyde can effectively be converted
to the corresponding carbonyl compounds in good to excellent yields (Table 3, Entries
1
–15, Table 4, Entries 1–13). As it can be observed, the deprotection of dithioketals is
more difficult than dithioacetals (Table 3, Entries 16–21, Table 4, Entries 14–17) under
both polymeric systems.
It should be mentioned that deprotection of thioketals without enolizable hydrogens
proceeded very well to give the corresponding ketone in high to excellent yield (Table 3,
Entry 16). However, for those with enolizable hydrogens, deprotection was accompanied
with the formation of an undesired minor ring-expanded product. This was in accordance
with the observations reported in the literature.[7,19–21] Interestingly, formation of this
minor ring-expanded product was seen using the PNBA/DMSO system, but completely
failed for the PNBA/H O system (Table 3, Entries 17–21, Table 4, Entries 14–17). This
2
protocol avoids the use of a solvent and excess of a toxic oxidant, and no further oxidation
of carbonyl compounds was observed.
Plausible mechanisms are summarized in Scheme 2 and 3 for the deprotection of thioac-
etals by PNBA/DMSO and PNBA/H O systems. Similar mechanisms would occur for the
2
PNBS/DMSO or PNBS/H O system. As it can be observed in Scheme 2, bromination of (I)
2
produced the intermediate (II), which later reacted with a molecule of DMSO to give the
sulfenyl bromide intermediate (III), which created the corresponding carbonyl compound,
1
,2-dithiacyclopentane (IV), together with the formation of the intermediate (V).
In Scheme 3, the suggested mechanism using PNBA as the reagent in aqueous media
+
has been shown. We have suggested that the electrophilic bromine (Br ) in PNBA would
be attacked by the dithiane, generating II and making it a good leaving group which is
subsequently attacked by a water molecule, resulting in the carbonyl compound.
In aromatic substrates, the electronic property of the substitutes and their position with
respect to the benzene ring affect the reaction time. As it is evident, the presence of func-
tional groups such as NO and MeO affected the reaction rates as electron-withdrawing
2
and electron-releasing groups (Table 3, Entries 5,12, Table 4, Entries 4,10). These observa-
tions were supported and were in accordance with the formation of the intermediate (II)
(
Schemes 2 and 3).
It should be mentioned that when the PNBA/DMSO or PNBS/DMSO system is used
for the deprotection of dithioacetals the PNBA does not lose its catalytic ability, and it
can be recovered and reused up to five to six times without any change in its efficiency
(
Table 5). The PNBS has been more catalytically efficient than PNBA for deprotection of

JOURNAL OF SULFUR CHEMISTRY
5
a
b
Table 3. Deprotection of 1,3-dithiolane and 1,3- dithiane using PNBA/DMSO and PNBA/H2O at room
temperature.c
Time (min)
(DMSO)
Yield (%)d
(DMSO)
Time (min)
(H2O)
Yield (%)d
(H2O)
Entry
1
Substrate
Product
35
90
75
90
2
3
20
95
60
87
25
90
60
85
4
5
20
20
90
93
70
60
88
92
6
7
55
60
90
85
90
90
93
85
8
9
40
35
79
90
70
90
88
91
(Continued)

6
F. EBRAHIMZADEH
Table 3. Continued.
Time (min) Yield (%)d Time (min) Yield (%)d
Entry
Substrate
Product
(DMSO)
(DMSO)
(H2O)
(H2O)
10
120
89
180
79
1
1
80
60
60
90
80
94
120
300
120
90
83
91
1
2
3
1
1
4
5
40
30
93
89
90
90
87
89
1
16
120
85
180
90
1
7
8
120
60
60c
68c
240
240
87
89
1
(Continued)

JOURNAL OF SULFUR CHEMISTRY
7
Table 3. Continued.
Time (min) Yield (%)d Time (min) Yield (%)d
Entry
Substrate
Product
(DMSO)
(DMSO)
(H2O)
(H2O)
19
180
65c
240
89
2
0
40
50c
100
480
91
85
21
300
50e
22
120
87
300
87
a
Reaction conditions: 1,3-dithiolane and 1,3-dithiane (1 mmol); PNBA (0.2 mmol); DMSO (3 mmol).
Reaction conditions: 1,3-dithiolane and 1,3-dithiane (1 mmol); PNBA (2 mmol); H2O (5 mL).
The identity of products was determined by comparison of their physical and spectral data with those of the authentic
samples.
Isolated yields.
A minor ring-expanded product is also obtained < 30%.
b
c
d
e
dithiolane and dithiane. It is seems that PNBS releases elecrophilic bromine more easily in
deprotection reaction rather than PNBA.
However, the spent PNBA or PNBS reagent in water media can be regenerated easily
by filtration and subsequent bromination. (Scheme 4). From a comparison between two
kinds of polymeric reagents in aqueous medium based on the results presented in Tables 3
and 4, we found that due to the best swelling effect, PNBA acts better than PNBS in aqueous
condition.
It seemed plausible that the described system could promote chemoselective deprotec-
tion with a controlled time of reaction of 1,3-dithioacetal in the presence of acid-sensitive
substrates such as S,O- acetals and O,O-acetals. By monitoring the reaction by GC,
2
-phenyl-1,3-dithiolane was converted into the corresponding aldehyde in the presence of
2-phenyl-1,3-dioxolane, 2-(p-tolyl)-1,3-dioxolane, and 2-phenyl-1,3-oxathiolane and with
almost complete chemoselectivity (Scheme 5).
Conclusions
In conclusion, we have introduced an efficient chemoselective method for the deprotec-
tion of 1,3-dithianes and 1,3-dithiolanes using PNBA and PNBS in the presence of DMSO
and water as oxidant. These polymeric reagents have the advantage of being heteroge-
neous which resulted in easy isolation of them from the reaction mixture. In addition,

8
F. EBRAHIMZADEH
a
b
Table 4. Deprotection of 1,3-dithiolane and 1,3-dithiane using PNBS/DMSO and PNBS/H2O at room
temperature.c
Time (min)
(DMSO)
Yield (%)d
(DMSO)
Time (min)
(H2O)
Yield (%)d
(H2O)
Entry
1
Substrate
Product
20
89
90
93
2
25
95
80
85
3
4
30
15
90
95
80
75
85
80
5
6
20
30
93
92
60
90
92
85
7
8
40
30
90
90
90
80
80
100
9
30
80
80
85
(Continued)

JOURNAL OF SULFUR CHEMISTRY
9
Table 4. Continued.
Time (min) Yield (%)d Time (min) Yield (%)d
Entry
Substrate
Product
(DMSO)
(DMSO)
(H2O)
(H2O)
10
50
85
100
70
11
80
90
150
80
1
2
3
30
25
90
90
80
80
85
87
1
1
4
5
90
95
50e
60e
300
300
75
70
1
16
60
65e
120
85
1
7
8
300
120
60e
300
300
65
65
1
90
a
Reaction conditions: 1,3-dithiolane and 1,3-dithiane (1 mmol); PNBS (0.1 mmol); DMSO (3 mmol); at room temperature.
Reaction conditions: 1,3-dithiolane and 1,3- dithiane (1 mmol); PNBS (3 mmol); H2O (5 mL); at room temperature.
The identity of products was determined by comparison of their physical and spectral data with those of the authentic
samples.
Isolated yields.
A minor ring-expanded product is also obtained < 30%.
b
c
d
e

10
F. EBRAHIMZADEH
Scheme 2. Proposed mechanisms for deprotection of thioacetals by PNBA/DMSO.
Scheme 3. Proposed mechanisms for deprotection of thioacetals by PNBA/H2O.
they are easily regenerated by a simple reaction. This protocol also offers advantages such
as operational simplicity, easy work-up of the products, long shelf life of the functional
polymer, mild reaction conditions, and the elimination of the hazardous characteristic of
the analogous low molecular deprotecting reagent.

JOURNAL OF SULFUR CHEMISTRY
11
Table 5. Reusability of PNBA/DMSO or PNBS/DMSO for deprotection of phenyl-l,3-dithiolane to ben-
zaldehyde.
Cycle
PNBA/DMSO conversion (%)
PNBA/DMSO yield (%)
PNBS/DMSO conversion (%)
PNBS/DMSO yield (%)
1
2
3
4
5
100
100
100
100
90
90
92
90
89
80
100
90
90
80
80
89
85
85
75
75
Scheme 4. Regeneration of spent PNBA or PNBS reagent in water media.
Experimental
All chemicals were supplied by either Merck or Fluka. The progress of the reactions was
followed by TLC, using silica gel SILG-UV 254 plates. Silica gel 60 was used for col-
umn chromatography. The identities of the products were determined by comparison of
their physical and spectral data with those reported in the literature. FT-IR spectra were
recorded on a Shimadzu DR-8001 spectrometer. NMR spectra were recorded on a Bruker
Avance DPX 250 MHz instrument. PNBA and PNBS were prepared as per our previous
report[34–37] and the capacity determined by the iodometric method.
Procedure for the preparation of PNBA
To a stirred suspension of polyacrylamide (5 g), NaOH (70 mmol, 2.8 g), Na CO
2
3
(
105 mmol, 11.13 g) and KBr (75 mmol, 12.5 g) in H O (180 mL), cooled in an ice bath,
2
ꢀ
was added dropwise in a solution of Oxone (75 mmol, 46.05 g) in H O (150 mL). A white
2
solid precipitated during the addition of the oxidant solution, forming a dense suspension,
which was stirred for 24 h. The product was isolated by filtration, washed with cold H O
2

12
F. EBRAHIMZADEH
Scheme 5. Chemoselective deprotection of reaction of 1,3-dithioacetal in the presence of S,O- acetals
and O,O-acetals.
and dried in an air oven at 60°C to yield 8.8 g of PNBA as orange powder (isolated yield
83%). The capacity of polymer was 5.4 mmol per gram, determined iodimetrically.
General procedure for the deprotection of dithiane and dithiolane using PNBA or
PNBS as a catalyst in DMSO
PNBA (0.035 g, 0.2 mmol) or PNBS (0.015 g, 0.1 mmol) was added to a solution of thioac-
etal or thioketal (1 mmol) and anhydrous DMSO (0.23 g, 3 mmol). The mixture was stirred
at room temperature for the appropriate reaction time (Tables 3 and 4). After completion
of the reaction (as monitored by TLC), CH Cl was added into the reaction mixture, and
2
2
it was quenched with a solution of NaOH (5% w/v, 10 mL). The organic layer was sep-
arated, and the aqueous layer was extracted with CH Cl (2 × 25 mL). The combined
2
2
organic extracts were then washed with brine (1 × 10 mL), next with water (2 × 15 mL),
and dried over Na SO /MgSO . The almost pure product was prepared after evaporation
2
4
4
of the solvent (Tables 3 and 4). If needed, further purification was achieved by column chro-
matography using EtOAc-n-hexane (1:10) as eluent. The catalyst PNBA or PNBS could be
recovered easily by filtration after completion of the reaction, followed by washing with

JOURNAL OF SULFUR CHEMISTRY
13
CH Cl , and drying at 30°C. The activity of the reused resin was the same as the fresh
2
2
polymer (Table 5). The identities of products were determined by comparison of their
physical and spectral data with those of the authentic samples. All the products are known
compounds.
General procedure for the deprotection of 1,3-dithiane and 1,3- dithiolane using
PNBA or PNBS as a reagent in the water
To a well-stirred PNBA (0.37 g, 2 mmol) or PNBS (0.48 g, 3 mmol) in H O (5 mL), the
2
thioacetal (1 mmol) was added. The mixture was stirred at room temperature until comple-
tion of the reaction (monitored by TLC). The reaction mixture was extracted with CH Cl
2
2
and washed with water, dried over Na SO , and evaporated. The almost pure product was
2
4
prepared after evaporation of the solvent (Tables 3 and 4). If needed, further purifica-
tion was achieved by column chromatography using EtOAc/n-hexane (1:10) as eluent. The
polymer could be regenerated by filtration after completion of the reaction and bromina-
tion of polyacrylamide by Oxone/KBr and poly(succinimide) by Br /CCl and they could
2
4
be reused again.
Spectral data of some starting material
−
1
Phenyl-1,3-dithiolane: IR (KBr, cm ): 3427, 3061, 3026, 2921, 1690, 1661, 1601, 1494, 1451
−
1
(
C=C– stretching of aromatic ring), 1423 (C=C– stretching of aromatic ring), 1276 cm
;
1
H NMR (CDCl , 250 MHz), δ: 3.24–3.46 (m, 4H), 5.61 (s, 1H), 7.20–7.30 (m, 3H), 7.49
3
1
3
(
d, J = 7.10 Hz, 2H) ppm; C NMR (CDCl , 63 MHz), δ: 40.8, 56.8, 128.6, 128.6, 129.1,
3
1
41.0 ppm.
4
−
1
-Methoxyphenyl-1,3-dithiolane: IR (KBr, cm ): 1609, 1522(C=C– stretching of aro-
−
1 1
matic ring), 1255, 1181, 1029 cm ; H NMR (CDCl , 250 MHz), δ: 3.30–3.36 (m, 2H),
3
3
8
.47–3.52 (m, 2H), 3.78 (s, 3H), 5.65 (s, 1H), 6.83 (d, J = 8.7 Hz, 2H), 7.44 (d, J =
.7 Hz, 2H).
1
4
-Methoxyphenyl-1,3-dithiane: H NMR (CDCl , 250 MHz), δ: 1.59 1.86 (m, 2H), 2.72
3
1
3
2
6
.89 (m, 4H), 3.66 (s, 3H), 4.99 (s, 1H), 6.72 (d, 2H), 7.24 (d, 2H) ppm; C NMR (CDCl3,
3 MHz), δ: 24.0, 31.2, 49.7, 54.3, 113.1, 127.9, 130.3, 158.5 ppm.
−
1
4
-Methylphenyl-1, 3-dithiolane: IR (KBr, cm ): 3005, 1511, 1437(C=C– stretching of
1
aromatic ring), 1412, 1278, 1177, 1164, 830, 777; H NMR (CDCl , 250 MHz), δ: 2.38 (s,
3
3
1
3
H), 3.28–3.46 (m, 2H), 5.61 (s, 1H), 7.12 (d, 2H), 7.40 (d, 2H) ppm; C NMR(100 MHz,
CDCl , δ/ppm): 21.1, 40.2, 56.1, 127.8, 129.1, 137.1, 137.8 ppm.
3
1
4
-Methylphenyl-1, 3-dithiane: HNMR (CDCl , 250 MHz), δ: 1.86–2.0 (m, 1H), 2.1–2.2
3
(
m, 1H), 2.8–3.2 (m, 4H), 3.8 (s, 3H), 5.2 (s, 1H), 6.8 (d, J = 7.3 Hz, 2H), 7.2 (d, J = 7.3 Hz,
H) ppm.
-Chlorophenyl-1,3-dithiolane: IR (KBr, cm ): 3006, 2904, 1487 (C=C– stretching of
2
−
1
4
−
1 1
aromatic ring), 1404, 1085, 1013, 754 cm ; H NMR (CDCl , 250 MHz), δ: 3.21–3.70
3
1
3
(
(
m, 4H), 5.59 (s, 1H), 7.32 (d, J = 8.4 Hz, 2 H), 7.41 (d, J = 8.4 Hz, 2 H) ppm; C NMR
CDCl , 63 MHz), δ: 41.8 , 55.4, 128.6, 129.3, 133.6, 139.0 ppm.
3
−
1
4
-Nitrophenyl-1,3-dithiolane: IR (KBr, cm ): 3103, 2924, 2852, 1931, 1606, 1593,
–1 1
1
2
2
519 (C=C– stretching of aromatic ring), 1350, 1108, 867, 727 cm ; H NMR (CDCl ,
3
50 MHz), δ: 3.4–3.66 (m, 4 H), 5.66 (s, 1 H), 7.65 (d, J = 8.3 Hz, 2 H), 8.17 (d, J = 8.3 Hz,
1
3
H) ppm; C NMR (CDCl , 100 MHz), δ: 40.5, 54.9, 123.7, 128.9, 147.3, 148.7 ppm.
3

14
F. EBRAHIMZADEH
2
-Phenyl-2-p-tolyl-[1,3]dithiolane: IR (KBr, cm−1): 697, 742, 1031, 1187, 1276,
1
1
(
3
1
444(C=C– stretching of aromatic ring), 1507, 1594, 2874, 2922, 3023, 3057; H NMR
CDCl , 200 MHz), δ: 2.31 (s, 3H), 3.39 (m, 4H), 7.08 (d, J = 8.1 Hz, 2H,), 7.23–7.27 (m,
3
1
3
H), 7.48 (d, J = 8 Hz, 2H), 7.60 (m, 2 H) ppm; C NMR (CDCl , 63 MHz), δ: 21.0, 40.1,
3
27.1, 127.7, 128.0, 128.2, 128.7, 137.0, 141.5, 144.8 ppm.
−
1
2
-Methyl-2-phenyl-[1,3]dithiolane: IR (KBr, cm ): 3062, 2925, 1683, 1599, 1583, 1449
1
(
C=C stretching of aromatic ring), 1359, 1266, 760, 690, 586; H NMR (CDCl , 250 MHz),
3
1
3
δ: 2.14 (s, 3H), 3.33–3.47 (m, 4H), 7.20–7.30 (m, 3H), 7.73–7.76 (m, 2H) ppm; C NMR
CDCl , 100 MHz), δ: 33.9, 40.3, 68.6, 126.8, 127.0, 128.0, 146.0 ppm.
(
3
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
The authors are thankful to the Research Councils of Islamic Azad University, Marvdash branch and
Shiraz University for their partial support of this work.
References
[
[
[
[
[
[
1] Greene TW, Wuts PGM. Protective groups in organic synthesis. New York: Wiley; 1999;
29–344, 724–727.
2] Burghardt TE. Developments in the deprotection of thioacetals. J Sulfur Chem. 2005;26:
3
4
11–427.
3] Bandgar BP, Kasture SP. Natural kaolinitic clay: a remarkable reusable solid catalyst for the
selective cleavage of thioacetals without solvent. Green Chem. 2000;2:154–156.
4] Varma RS, Saini RK. Solid state dethioacetalization using clayfen. Tetrahedron Lett.
1
997;38:2623–2624.
5] Meshram HM, Reddy GS, Yadav JS. Clay supported ammonium nitrate ‘Clayan’: a mild and
eco-friendly reagent for dethioacetalization. Tetrahedron Lett. 1997;38:8891–8894.
6] Meshram HM, Reddy GS, Sumitra G, Yadav JS. Microwave thermolysis: arapid and
general method for dethioacetalization using ‘Clayan’ in dry media. Synth Commun.
1
999;29:1113–1119.
[
[
[
7] Ganguly X, Datta M. Ecofriendly solid-state oxidative deprotection of 1,3-dithianes and 1,3-
dithiolanes using ammonium persulfate on wet montmorillonite K-10 clay support under
microwave irradiation. Synlett. 2004;15:659–662.
8] Liu J, Wong CH. An efficient method for the cleavage of p-methoxybenzylidene (PMP),
tetrahydropyranyl (THP) and 1,3-dithiane protecting groups by Selectfluor™. Tetrahedron Lett.
2
002;43:4037–4039.
9] Lee JG, Hwang JP. Highly efficient regeneration of carbonyl compounds from oximes, tosylhy-
drazones, 1,3-dithiolanes, and 1,3-dithianes using cupric nitrate supported on silica gel. Chem
Lett. 1995;24:507–508.
[
10] Hajipour AR, Zarei A, Khazdooz L, Ruoho AE. Silicasulfuric acid/NaNO3 as a new reagent for
the deprotection of S,S-acetals under mild conditions. Synthesis. 2006;38:1480–1484.
11] Mansilla GO, Peñéñory AB. Simple and efficient deprotection of 1,3-dithianes and 1,3-
dithiolanes by copper(II) salts under solvent-free conditions. Tetrahedron Lett. 2007;48:
[
6
150–6154.
[
12] Hirano M, Ukawa K, Yakabe S, Morimoto TA. Convenient deprotection of 1,3-dithiane deriva-
tives with ferric nitrate under heterogeneous conditions. Synth Commun. 1997;27:1527–1533.

JOURNAL OF SULFUR CHEMISTRY
15
[
13] Firouzabadi H, Iranpoor N, Hazarkhani H, Karimi B. Reactions of silica chloride
SiO2Cl)/DMSO, a heterogeneous system for the facile regeneration of carbonyl com-
pounds from thioacetals and ring-expansion annelation of cyclic thioacetals. J Org Chem.
002;67:2572–2576.
(
2
[
14] Ballini R, Petrini M. A new procedure for dethioacetalization via equilibrium exchange
with aqueous acetone, paraformaldehyde and amberlyst 15 as acidic catalyst. Synthesis.
1
990;22:336–337.
[
[
15] Giri VS, Sankar P. Convenient procedure for dethioketalisation in nitrogen heterocycles. Synth
Commun. 1993;23:1795–1978.
16] Karami B, Taei M, Khodabakhshi S, Jamshidi M. Synthesis of 1,3-dithiane and 1,3-
dithiolane derivatives by tungstate sulfuric acid: recyclable and green catalyst. J Sulfur Chem.
2
012;33:64–74.
[
[
[
17] Habibi MH, Tangestaninejad S, Montazerozohori M, Mohamadpoor-Baltork I. highly efficient,
and fast solid state deprotection of 1,3-Dithianes and 1,3-Dithiolanes using mercury(II) nitrate
trihydrate. Molecules. 2003;8:663–669.
18] Curini M, Marcotullio MC, Pisani E, Rosati O, Costantino U. Heterogeneous catalysis in
carbonyl regeneration from 1,3-dithiolanes and 1,3-dithianes by zirconium sulfophenyl phos-
phonate. Synlett. 1997;8:769–770.
19] Iranpoor N, Firouzabadi H, Shaterian HR. Catalytic and chemoselective deprotection of S,S-
and S,O-acetals and ketals in the presence of their O,O-analogs with electrophilic halogens
under neutral conditions. Tetrahedron Lett. 2003;44:4769–4773.
20] Veisi H, Ghorbani-Vaghei R. Recent progress in the application of N-halo reagents in the
synthesis of heterocyclic compounds. Tetrahedron. 2010;66:7445–7463.
[
[
[
21] Karimi B, Seradj H, Tabaei MH. N-bromosuccinimide (NBS), an efficient reagent for the
conversion of 1,3-oxathiolanes to carbonyl compounds. Synlett. 2000;11:1798–1801.
22] Karimi B, Hazarkhani H. New applications of 2,4,6-trichloro-1,3,5-triazine (TT) in synthesis:
highly efficient and chemoselective deprotection and ring-enlargement of dithioacetals and
oxathioacetals. Synthesis. 2003;35:2547–2551.
ꢀ
[23] Ghorabni-Vaghei R, Zolfigol MA. Mild and efficient deprotection of 1,3-dithianes with N,N -
ꢀ
diiodo-N,N -1,2-ethanediyl-bis(p-toluenesulphonamide). J Chin Chem Soc. 2005;52:327–330.
[24] Ghorbani-Vaghei R, Khazaei A. Facile and efficient method for deprotection of 1,3-
ꢀ
ꢀ
oxathiolanes with N,N -dibromo- N,N - ethanediylbis (p-toluensulphonamide). Phosphorus,
Sulfur Silicon Relat Elem. 2004;179:1787–1791.
[
[
[
[
[
[
[
25] Desai UV, Pore DM, Tamhankar BV, Jadhavb SA, Wadgaonkar PP. An efficient deprotec-
tion of dithioacetals to carbonyls using oxone–KBr in aqueous acetonitrile. Tetrahedron Lett.
2
006;47:8559–8561.
26] Nicolaou KC, Mathison CJ, Montagnon N. New reactions of IBX: oxidation of nitrogen- and
sulfur-containing substrates to afford useful synthetic intermediates. Angew Chem Int Ed.
2
003;42:4077–4082.
27] Srilakshmi NK, Nageswar KS, Rao YVD, Rama K. Mild and efficient hydrolysis of aromatic
thioacetals/thioketals using o-iodoxybenzoic acid (IBX) in presence of β- cyclodextrin in
water. Synthesis. 2003;2295–2297.
28] Ganguly NG, Barik SK. A facile mild deprotection protocol for 1,3-dithianes and 1,3-
dithiolanes with 30% hydrogen peroxide and iodine catalyst in aqueous micellar system.
Synthesis. 2009;41:1393–1400.
29] Ganguly NC, Datta M. Mild and eco-friendly oxidative cleavage of 1,3-dithianes and 1,3-
dithiolanes with a catalytic amount of hydrobromic acid and hydrogen peroxide: synergetic
effect of bromonium ion equivalent and hydrogen peroxide. J Chem Res. 2005;2005:218–221.
30] Shaterian HR, Hadadzadeh H. Efficient chemoselective mild deprotection of S,S and S,O-
acetals and ketals with electrophilic halogens. Phosphorus Sulfur Silicon Relat Elem.
2
006;181:1059–1071.
31] Bahrami K, Khodaei MM, Tajik M, Shakibaian VA. Novel approach towards dethioacetaliza-
tion reactions with H2O2–SOCl2 system. Chin Chem Lett. 2012;23:81–85.

16
F. EBRAHIMZADEH
[
[
[
32] Ghorbani-Vaghei R, Veisi H. Solvent-free oxidative deprotection of 1,3-dithianes and
ꢀ ꢀ ꢀ
,3-dithiolanes using poly(N,N -dibromo-N-ethyl-benzene-1,3-disulfonamide), N,N,N ,N -
1
tetrabromobenzene-1,3-disulfonamide and NBS. Arkivoc. 2009;10:44–51.
33] Nishide K, Yokota K, Nakamura D, Sumiya T, Node M, Ueda M, Fuji KA. New entry for the
deprotection of monothioacetals and dithioacetals: silver nitrite-iodine system. Tetrahedron
Lett. 1993;34:3425–3428.
34] Tamami B, Firouzabadi H, Ebrahimzadeh F, Fadavi A. Poly(N-bromoacrylamide): an effi-
cient and useful catalyst for the protection of carbonyl compounds as dithiolanes, dithianes
and oxathiolanes under solvent-free and microwave conditions. J Iran Chem Soc. 2009;6:
7
22–728.
[
35] Ebrahimzadeh F. New applications of poly(N-bromoacrylamide) in organic synthesis: highly
efficient and regioselective transformation of alkenes into bromohydrins, bromoethers and
bromoacetates. Der Chemica Sinica. 2012;3:1140–1145.
[
36] Ebrahimzadeh F, Rooydell R. Poly(N-bromoacrylamide) as highly efficient, regioselective
and recyclable catalyst for preparation of β-azidoalcohols, β-cyanoalcohols, β-nitroalcohols
and β-nitratoalcohols from epoxides under aqueous conditions. Der Chemica Sinica.
2
012;3:1146–1152.
[37] Tamami B, Nasrolahi Shirazi A, Ebrahimzadeh F. Synthesis and applications of cross-
linked poly(N-bromomaleimide) in oxidation of various organic compounds. Iran Polym J.
2
009;18:957–967.