Silica-supported perchloric acid (HClO4-SiO2): A versatile catalyst for tetrahydropyranylation, oxathioacetalization and thioacetalization

Article abstract of DOI:10.1055/s-2006-942465

A simple and convenient synthetic protocol for the protection of hydroxyl group as tetrahydropyranyl ether as well as carbonyl functionality as oxathioacetal and thioacetal has been achieved using a catalytic amount of silica-supported perchloric acid und

Full text of DOI:10.1055/s-2006-942465

PAPER
2497
Silica-Supported Perchloric Acid (HClO -SiO ): A Versatile Catalyst for
4
2
Tetrahydropyranylation, Oxathioacetalization and Thioacetalization
S
A
ilica-Supported P
b
erchloric
A
c
u
id T. Khan,* Tasneem Parvin, Lokman H. Choudhury
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039, India
Fax +91(361)2690762; E-mail: atk@iitg.ernet.in
Received 10 February 2006; revised 27 March 2006
This work is dedicated to Prof. D. N. Buragohain, former Director of IITG, on the occasion of his 65 birthday.
th
DHP
Abstract: A simple and convenient synthetic protocol for the pro-
tection of hydroxyl group as tetrahydropyranyl ether as well as car-
bonyl functionality as oxathioacetal and thioacetal has been
achieved using a catalytic amount of silica-supported perchloric
acid under solvent-free conditions. This protocol has many advan-
tages compared to currently available methodologies in terms of
simplicity, yield, reaction time, reusability of the catalyst and eco-
nomic viability.
ROH
1
ROTHP
HClO4-SiO2, r.t.
2
R1
O
HS(CH2)2OH
HClO4-SiO2, r.t.
R1
R2
R2
S
4
O
R1
S
HS(CH ) SH
2 n
3
HClO4-SiO2, r.t.
R2
n
Key words: alcohols, phenols, THP ethers, carbonyl compounds,
S
oxathioacetals, thioacetals
5
1
2
R = alkyl, aryl; R = alkyl, aryl; R = H, alkyl, aryl; n = 1, 2
Scheme 1
1
Recently silica-supported catalysts as well as perchloric
acid impregnated on silica gel has gained considerable at-
tention in current organic synthesis due to its ease of prep-
aration, high efficiency, reusability of the catalyst and its
economic viability. The versatility and overall synthetic
utility of this reagent is exemplified by the following ap-
plications such as acetylation of phenols, thiols, alcohols
Catalyst, r.t.
DHP
OH
OTHP
2
3
and amines, peracetylation of carbohydrates, acetalation
4
5
followed by acetylation, for glycosylation, Ferrier rear-
6
7
CHO
O
S
rangement of glycals, and synthesis of heterocycles as
well as selective cleavage of isopropylidene and trityl
ethers. Recently we found that the same catalyst is useful
for gem-diacylation of aldehydes as well as for Michael
addition of thiols to the electron-deficient alkenes. In
our earlier preliminary communication, we reported that
0% aqueous perchloric acid is an effective catalyst for
oxathioacetalization of carbonyl compounds. In continua-
Catalyst, r.t.
8
HSCH2CH2OH
9
10
NO2
NO2
1
1
Scheme 2
7
tion of our work on solvent-free conditions and utilization tetrahydropyranylation and oxathioacetalization, respec-
of heterogeneous catalysis, herein report silica-supported tively (Scheme 2). For both the transformations the same
perchloric acid as a catalyst for the protection of hydroxyl sets of experiments were carried out and the results are
and carbonyl compounds as THP ethers and oxathioace- summarized in Table 1.
tals or dithioacetals, respectively at room temperature un-
Sometimes the protection of hydroxyl group as its THP
der mild conditions as shown in Scheme 1.
ether is preferred due to easy installation, low cost of the
The catalyst HClO -SiO was prepared by following the reagent DHP, stability towards a wide variety of reaction
4
2
2
literature procedure. To prove the better catalytic activity conditions as well as easy removal at the later stage. Tet-
of silica-supported perchloric acid over aqueous perchlo- rahydropyranylation of alcohols and phenols is tradition-
1
2
13
ric acid as well as to find out an optimal condition for both ally carried out in the presence of PTSA, PPTS, K-10
1
4
15
16
the transformations, i.e. tetrahydropyranylation and oxa- clay and BF ·OEt . Recent alternatives include ZrCl ,
3
2
4
thioacetalization, a set of reactions were studied under I2,17 LiBr,
18
acetonyltriphenylphosphonium bromide
19
20
different catalytic conditions. Menthol and 4-nitro- (ATPB), tetrabutylammonium tribromide (TBATB),
2
1
22
benzaldehyde were chosen as model substrates for aluminum chloride hexahydrate, Bi(OTf)3, dialkyl-
2
3
imidazolium tetrachloroaluminates, InCl immobilized
in ionic liquid,
3
24
25
SYNTHESIS 2006, No. 15, pp 2497–2502
x
x.
x
x
.
2
0
0
6
H
2
O, bromodimethylsulfonium bro-
2
6
27
Advanced online publication: 04.07.2006
DOI: 10.1055/s-2006-942465; Art ID: P01506SS
Georg Thieme Verlag Stuttgart · New York
mide, cupric sulfate pentahydrate, and bismuth nitrate
pentahydrate.28 Although most of the methods provide
©

2
498
A. T. Khan et al.
PAPER
Table 1 Tetrahydropyranylation of Menthol and Oxathioacetalization of 4-Nitrobenzaldehyde
Entry
Catalyst
O
S
O2N
THPO
Time
Yield (%)a
Time
12 h
Yield (%)a
1
2
3
4
No catalyst
12 h
0
5
0
SiO (20 mg/mol)
12 h
12 h
10
2
Aqueous HClO (10 mol%)
10 min
5 min
76
91b
1 h
3511
65
4
HClO -SiO (20 mg/mmol, 1 mol%)
30 min
4
2
a
Isolated yield.
b
The catalyst can be recycled up to consecutive three cycles without lose of its activity and provided 85% and 82% yields within 5 and 10 min,
respectively, for THP protection.
good yields, still some of them require harsh reaction con- low yield in case of 4-nitrobenzaldehyde as mentioned in
ditions, long reaction times, involvement of expensive Table 1. HClO -SiO is a better catalyst as shown in
4
2
and moisture-sensitive catalysts. Hence cheap heteroge- Table 4. It is much more effective in terms of reaction
neous catalyst, which work under mild conditions are de- time and yield. Both aromatic aldehydes and ketones can
sirable.
be protected as oxathioacetals using this protocol without
any difficulty. All the products were isolated by distilla-
tion under reduced pressure.
To verify the scope of this reagent for tetrahydropyrany-
lation of alcohols and phenols, firstly cetyl alcohol was
treated with 1.1 equivalents of 3,4-dihydro-2H-pyran Various new methods have also been developed for thio-
(
DHP) under solvent-free conditions with 1 mol% of acetalization of carbonyl compounds. Among them, some
3
5
HClO -SiO at room temperature. It was smoothly con- of the recent methods employ: N-bromosuccinimide,
verted to the corresponding THP ether within five minutes bromodimethylsulfonium bromide, acetyl chloride,
in 91% yield. Similarly, a wide variety of other aliphatic copper (II) tetrafluoroborate, ruthenium(III) chloride,
as well as benzyl alcohols also gave the THP ethers within PTSA/SiO , silica-supported polyphosphoric acid and
a very short time. It is worthwhile to mention that this pro- other catalysts. Interestingly, a large number of carbonyl
tocol is faster and provide better yields compared to re- compounds underwent dithioacetalization using 1 mol%
cently reported methods. Likewise, various secondary HClO -SiO under solvent-free conditions at room tem-
4
2
3
6
37
39
38
40
41
2
42
4
2
alcohols such as menthol, cyclohexanol, cholesterol and perature. Most of the reactions were complete within 2–30
even hindered alcohol benzhydrol also underwent tetrahy- min in very good yields as shown in Table 5. Remarkably,
dropyranylation without any difficulty. Moreover, isopro- aldehydes having electron-donating or -withdrawing sub-
pylidine-protected glycerol provided the desired THP stituents in the aromatic ring underwent thioacetalization
ether under similar experimental conditions keeping the smoothly in good yields although the yield for the 1,3-
acid-sensitive protecting group intact. 4-Methoxyphenol dithiane of 4-nitrobenzaldehyde is less than that of other
and b-naphthol were also converted to the required THP protected aldehydes. It is noteworthy to mention that the
ethers in good yields (Table 2).
same procedure is applicable to aliphatic aldehydes also.
The acid-sensitive 2-furaldehyde can also be protected to
the desired 1,3-dithiane derivatives without any difficulty.
In Table 3, menthol and 2,3-O-isopropylidene-D-(±)-
glycerol are used as model substrates for comparison of
this protocol with some of the recently reported methods.
We have done the comparison with respect to mol% of
catalyst used, reaction timing and yields obtained.
Several methods are known in the literature29 for both
oxathioacetalization and thioacetalization. Conventional-
ly, oxathioacetals are prepared from the corresponding
carbonyl compounds and 2-mercaptoethanol by using
1
All the products were fully characterized by recording H
13
NMR, C NMR and elemental analysis. Remarkably, all
solid dithioacetals can be obtained by direct recrystalliza-
tion after filtering the catalyst. The generality and scope of
this catalyst can be ascertained from its recyclability,
which we have tested by the following way. For example,
a mixture of 4-hydroxybenzaldehyde and propane-1,3-
dithiol was treated with HClO -SiO . After completion of
4
2
3
0
equimolar amount of Lewis acid such as BF ·OEt or
3
2
the reaction, anhydrous diethyl ether was added to the
mixture and the catalyst was filtered off, dried and used
for a second time. The recovered catalyst can be recycled
for another two more cycles without any loss of its cata-
lytic activity: yields were 92% and 90% respectively after
3
1
ZnCl . Some of the recent procedures for similar trans-
2
3
2
formation are: montmorillonite K-10, bromodimethyl-
3
3
sulfonium
bromide
and
silica-supported
3
4
tungstophosphoric acid. In our preliminary communica-
tion we reported the use of 70% aqueous perchloric acid
2
and 5 minutes.
1
1
for the same transformation. Notably, we got relatively
Synthesis 2006, No. 15, 2497–2502 © Thieme Stuttgart · New York

PAPER
Silica-Supported Perchloric Acid
2499
Table 2 Tetrahydropyranylation of Alcohols and Phenols Using HClO -SiO as Catalyst
4
2
Entry
Substrate 1
Reaction time (min)
Product 2a
Yield (%)b
a
5
9127
OH
OTHP
13
13
b
c
5
5
90
87
HO
HO
OH
THPO
OTHP
OH
OH
THPO
MeO
Cl
OTHP
OTHP
d
e
f
5
5
5
9525
MeO
Cl
92
OH
OTHP
8328
OH
OTHP
O2N
O
O2N
O
g
15
5
9613
9119
OH
OTHP
h
OH
OTHP
i
OH
5
OTHP
9113
j
15
9719
HO
THPO
k
l
OH
5
OTHP
95
15
8425
O
O
O
O
OH
OTHP
m
n
5
8013
8328
MeO
OH
OH
MeO
OTHP
OTHP
30
a
Products were characterized by recording IR, H and 13C NMR spectra and elemental analysis.
Isolated yield.
1
b
Synthesis 2006, No. 15, 2497–2502 © Thieme Stuttgart · New York

2
500
A. T. Khan et al.
PAPER
on a Nicolet Impact 410 spectrophotometer. H NMR spectra and
1
Table 3 Comparisons of Some of the Recent Methods for Tetrahy-
dropyranylation with HClO -SiO Protocol
1
3
C NMR spectra were recorded on a Varian 400 MHz spectrometer
4
2
in CDCl using TMS as internal reference. Elemental analyses were
3
Catalyst
Mol% Menthol
Time
2,3-O-Isopropy-
lidene-D-(±)-glycerol
carried out in a PerkinElmer 2400 automatic analyzer. Column
chromatographic separations were done on SRL silica gel (60–120
mesh).
a
Yield (%)a
Yield (%) Time
2
2
7
Silica-Supported Perchloric Acid (HClO -SiO )
CuSO ·5H O
20
0.1
1 h
1 h
2 h
89
74
74
50 min
–
85
–
4
2
4
2
HClO (1.8 g, 12.5 mmol, as a 70% aq solution) was added to a sus-
pension of SiO (230–400 mesh, 23.7 g) in Et O (70 mL). The mix-
ture was concentrated and the residue was heated at 100 °C for 72 h
under vacuum to furnish HClO -SiO (0.5 mmol/g) as a free-flow-
4
TBATB20
2
2
2
2
Bi(OTf) ·4H O
0.1
5
3.25 h
20 min
10 min
78
84
86
3
2
4
2
2
8
ing powder (50 mg = 0.025 mmol of HClO4).
Bi(NO ) ·5H O
22 min 90
5 min 91
3
3
2
HClO -SiO Catalyzed Tetrahydropyranylation of Alcohols
HClO -SiO2
1
4
2
4
and Phenols; General Procedure
a
Isolated yield.
To a mixture of alcohol or phenol 1 (1 mmol) and 2,3-dihydropyran
(
DHP) (1.1 mmol, 100 mL) was added HClO -SiO (0.01 mmol, 20
4
2
mg) and the mixture was stirred at r.t. After completion of the reac-
tion as checked by TLC, the crude mixture was directly passed
through a short basic alumina column to obtain the desired pure
THP ether 2 (Table 2).
In conclusion we have devised a simple and efficient
methodology for tetrahydropyranylation, oxathioacetal-
ization and thioacetalization using a very cheap, readily
accessible and recyclable catalyst. The notable advantag-
HClO -SiO Catalyzed Oxathioacetalization and Thioacetaliza-
4
2
tion of Carbonyl Compounds; General Procedure
es of this protocol are non-aqueous work-up; very rapid A stirred mixture of carbonyl compound 3 (10 mmol) and 2-mer-
and simple procedure, very good yields. Therefore, we be- captoethanol (12 mmol, 0.84 mL) was treated with HClO -SiO
200 mg, 0.1 mmol) at r.t. The progress of the reaction was moni-
4
2
(
lieve this methodology will be a new addition in organic
synthesis.
tored by TLC. After completion of the reaction, the pure product 4
was obtained directly by distillation (Table 4). In the case of dithio-
acetalization, a mixture of carbonyl compound 3 (5 mmol) and
ethane-1,2-dithiol (A) or propane-1,3-dithiol (B) (6 mmol) was
treated with the same catalyst. After completion of reaction as
checked by TLC, it was diluted with EtOAc and the catalyst was fil-
Melting points were recorded on a Büchi B-545 melting point appa-
ratus and were uncorrected. IR spectra were recorded in KBr or neat
Table 4 Oxathioacetalization of Carbonyl Compounds Using Catalytic Amount of HClO -SiO versus Aqueous HClO under Solvent-Free
4
2
4
Conditions
Entry
Product 4
Method Aa
Time (min)
Method Bb
Bp (°C/mm Hg) or Mp (°C)
Yield (%)c,d
68
Time (min)
10
Yield (%)c,d
a
b
c
O
S
20
60
–
7433
6533
9033
8533
135/1
78
MeO
O2N
Cl
O
35
–
30
S
25e
30
125/5
85/5
O
S
d
O
S
30
76
e
90
60
60
7533
110/5
O
S
a
Method A = reactions were carried out using 10 mol% aq HClO (Ref. 11).
4
b
c
d
e
Method B = reactions were carried out using 1 mol% HClO -SiO .
4
2
Isolated yield.
All the products were colorless oils, except 4b (solid), and were characterized by recording H NMR, 13C NMR and elemental analysis.
1
The catalyst was recycled up to consecutive three cycles without loss of its activity and it provided 80% and 78% yields within 25 and 30 min,
respectively.
Synthesis 2006, No. 15, 2497–2502 © Thieme Stuttgart · New York

PAPER
Silica-Supported Perchloric Acid
2501
Table 5 Thioacetalization of Carbonyl Compounds Using Catalytic Amount of HClO -SiO under Solvent-Free Conditions
4
2
Entry
Substrate 3
Thiola
A
Reaction time (min) Product 5b
Yield (%)c
9836
Mp (°C)d
liquid
a
15
S
CHO
3
3
S
b
c
B
B
B
A
10
S
S
8135
9436
9837
98
91
Cl
CHO
Cl
2
S
157 (158)36
HO
CHO
HO
S
d
e
5
S
77–78 (78)37
94
BnO
CHO
BnO
S
MeO
MeO
15
MeO
MeO
MeO
S
CHO
CHO
S
MeO
f
B
B
30
15
S
6142b
9636
148 (141–142)42b
liquid
O2N
O2N
S
g
S
CHO
O
O
S
h
i
B
A
30
5
S
9336
9136
liquid
O
S
88–89 (88)36
S
O
S
j
O
B
40
9637
109 (108–109)37
S
S
a
A = ethane-1,2-dithiol, B = propane-1,3-dithiol.
b
c
d
All products were solids, except 5a,g,h (liquids), and were characterized by recording H NMR, 13C NMR and elemental analysis.
1
Isolated yield.
Reported mps are given in parentheses.
tered off. Then the filtrate was concentrated and either kept for re-
crystallization by adding hexane if the product 5 is solid or purified
by silica gel column chromatography (Table 5).
THP Ether of But-2-yne-1,4-diol 2c
Colorless viscous liquid, yield: 0.221 g (87%).
IR (neat): 2940, 2873, 1445, 1399, 1352, 1271, 1209, 1127, 1025,
–
1
9
68 cm .
THP Ether of Pentane-1,5-diol 2b
Colorless viscous liquid; yield: 0.245 g (90%).
1
H NMR (400 MHz, CDCl ): d = 1.46–1.79 (m, 12 H, CH ), 3.43–
3
2
3
.48 (m, 2 H, OCH ), 3.73–3.79 (m, 2 H, OCH ), 4.19 (d, J = 17.6
2
2
IR (neat): 2940, 2879, 1455, 1445, 1352, 1265, 1204, 1132, 1035
Hz, 1 H, OCH ), 4.22 (d, J = 12.4 Hz, 2 H, OCH ), 4.27 (d, J = 14.2
–
1
2
2
cm .
Hz, 1 H, OCH ), 4.74 (t, J = 3.4 Hz, 2 H).
2
1
H NMR (400 MHz, CDCl ): d = 1.42–1.88 (m, 18 H, CH ), 3.39
13
3
2
C NMR (100 MHz, CDCl ): d = 18.88 (2 C), 25.20 (2 C), 30.07 (2
3
(
(
(
1
dt, J = 6.8, 9.6 Hz, 2 H, OCH ), 3.46–3.53 (m, 2 H, OCH ), 3.74
2
2
C), 54.19 (2 C), 61.81 (2 C), 81.81 (2 C), 96.66 (2 C).
dt, J = 6.8, 9.6 Hz, 2 H, OCH ), 3.83–3.90 (m, 2 H, OCH ), 4.56
2
2
Anal. Calcd for C H O (254.32): C, 66.12; H, 8.72. Found: C,
dd, J = 6.8, 9.6 Hz, 2 H, OCH).
14 22
4
6
6.21; H, 8.69.
3
C NMR (100 MHz, CDCl ): d = 19.71 (2 C), 23.00, 25.55 (2 C),
3
2
9.61 (2 C), 30.79 (2 C), 62.23 (2 C), 67.41 (2 C), 98.67 (2 C).
THP Ether of 4-Chlorobenzyl Alcohol 2e
Anal. Calcd for C H O (272.38): C, 66.14; H, 10.36. Found: C,
Colorless viscous liquid; yield: 0.209 g (92%).
15
28
4
6
6.21; H, 10.40.
IR (neat): 2943, 2867, 1592, 1464, 1358, 1132, 1075, 1038 cm–1.
Synthesis 2006, No. 15, 2497–2502 © Thieme Stuttgart · New York

2
502
A. T. Khan et al.
PAPER
1
H NMR (400 MHz, CDCl ): d = 1.54–1.89 (m, 6 H, CH ), 3.52 (d,
(6) (a) Agarwal, A.; Rani, S.; Vankar, Y. D. J. Org. Chem. 2004,
69, 6137. (b) Tiwari, P.; Agnihotri, G.; Misra, A. K.
Carbohydr. Res. 2005, 340, 749. (c) Misra, A. K.; Tiwari,
P.; Agnihotri, G. Synthesis 2005, 260.
3
2
J = 11.2 Hz, 1 H, OCH ), 3.87 (t, J = 8.4 Hz, 1 H, OCH ), 4.44 (d,
J = 12.0 Hz, 1 H, ArCH), 4.67 (br s, 1 H, OCHO), 4.72 (d, J = 12.4
Hz, 1 H, ArCH), 7.29 (br s, 4 H, ArH).
2
2
1
3
(7) Das, B.; Reddy, M. R.; Ramu, R.; Reddy, K. R.; Geethangili,
M. J. Chem. Res., Synop. 2005, 598.
C NMR (100 MHz, CDCl ): d = 19.40, 25.50, 30.58, 62.13, 67.99,
3
9
7.70, 128.30 (2 C), 128.89 (2 C), 133.02, 136.65
(8) Agarwal, A.; Vankar, Y. D. Carbohydr. Res. 2005, 340,
1661.
Anal. Calcd for C H ClO (226.70): C, 63.58; H, 6.67. Found: C,
6
1
2
15
2
3.38; H, 6.59.
(
9) Khan, A. T.; Choudhury, L. H.; Ghosh, S. J. Mol. Cat. A:
Chem. 2006, 255, 230.
THP Ether of Benzhydrol 2k
White solid; yield: 0.255 g (95%); mp 50–51 °C.
(
(
10) Khan, A. T.; Ghosh, S.; Choudhury, L. H. Eur. J. Org.
Chem. 2006, 2226.
11) Mondal, E.; Sahu, P. R.; Khan, A. T. Synlett 2002, 463.
IR (KBr): 2942, 2903, 2877, 1490, 1199, 1121, 1025, 977, 916
cm .
–
1
(12) Corey, E. J.; Niwa, H.; Knolle, J. J. Am. Chem. Soc. 1978,
00, 1942.
13) Miyashita, M.; Yoshikoshi, A.; Grieco, P. A. J. Org. Chem.
977, 42, 3772.
1
1
H NMR (400 MHz, CDCl ): d = 1.52–1.97 (m, 6 H, CH ), 3.47–
.52 (m, 1 H, OCH ), 3.85–3.91 (m, 1 H, OCH ), 4.66 (t, J = 3.2 Hz,
3
2
(
(
3
1
2
2
1
H, OCHO), 5.79 [s, 1 H, (Ar) CH], 7.17–7.36 (m, 10 H, ArH).
2
14) Hoyer, S.; Laszlo, P.; Orlovic, M.; Polla, E. Synthesis 1986,
1
3
C NMR (100 MHz, CDCl ): d = 19.27, 25.65, 30.66, 61.99, 78.07,
655.
3
9
1
5.37, 126.67 (2 C), 126.88 (2 C), 127.43 (2 C), 127.53 (2 C),
28.03 (2 C), 128.29 (2 C).
(15) Alper, H.; Dinkes, L. Synthesis 1972, 81.
(16) Rezai, N.; Meybodi, F. A.; Salehi, P. Synth. Commun. 2000,
3
0, 1799.
Anal. Calcd for C H O (268.35): C, 80.57; H, 7.51. Found: C,
1
8
20
2
(
(
17) Deka, N.; Sarma, J. C. Synth. Commun. 2000, 30, 4435.
18) Reddy, M. A.; Reddy, L. R.; Bhanumathi, N.; Rao, K. R.
Synth. Commun. 2000, 30, 4323.
8
0.71, H, 7.59.
2
-[3¢,4¢,5¢- Trimethoxyphenyl]-1,3-dithiolane (5e)
(
(
19) Hon, Y.-S.; Lee, C.-F.; Chen, R. J.; Szu, P.-H. Tetrahedron
White solid; yield: 1.335 g (98%); mp 53–54 °C.
2001, 57, 5991.
–
1
IR (KBr): 1586, 1505, 1127 cm .
20) Naik, S.; Gopinath, R.; Patel, B. K. Tetrahedron Lett. 2001,
1
H NMR (400 MHz, CDCl ): d = 3.31–3.38 (m, 2 H, SCH ), 3.46–
42, 7679.
3
2
3
5
.54 (m, 2 H, SCH ), 3.82 (s, 3 H, OCH ), 3.86 (s, 6 H, 2 × OCH ),
(21) Namboodiri, V. V.; Varma, R. S. Tetrahedron Lett. 2002,
43, 1143.
22) Stephens, J. R.; Butler, P. L.; Clow, C. H.; Oswald, M. C.;
Smith, R. C.; Mohan, R. S. Eur. J. Org. Chem. 2003, 3827.
23) Namboodiri, V. V.; Verma, R. S. Chem. Commun. 2002,
342.
2
3
3
.60 (s, 1 H, ArCH), 6.76 (s, 2 H, ArH).
(
1
3
C NMR (100 MHz, CDCl ): d = 40.18 (2 C), 56.12 (2 C), 56.86,
3
6
0.78, 104.71, 104.85 (2 C), 135.14, 152.85 (2 C).
(
Anal. Calcd for C H O S (272.37): C, 52.92; H, 5.92; S, 23.54.
12
16
3 2
Found: C, 52.98; H, 5.89; S, 23.61.
(24) Yadav, J. S.; Subba Reddy, B. V.; Gnaneshwar, D. New J.
Chem. 2003, 202.
(
(
(
(
(
(
25) Kavala, V.; Samal, A. K.; Patel, B. K. Arkivoc 2005, (i), 20;
www.arkat-usa.org.
26) Khan, A. T.; Mondal, E.; Borah, B. M.; Ghosh, S. Eur. J.
Org. Chem. 2003, 4113.
Acknowledgment
A.T.K. acknowledges to the Department of Science and Technolo-
gy (DST), New Delhi for research grant (Grant No. SP/S1/G-35/
27) Khan, A. T.; Choudhury, L. H.; Ghosh, S. Tetrahedron Lett.
9
8). L.H.C. is thankful to the CSIR, Govt. of India for a research fel-
2004, 45, 7891.
lowship. We are also grateful to the Director, IITG for providing ge-
neral facilities to carry out our research work.
28) Khan, A. T.; Ghosh, S.; Choudhury, L. H. Eur. J. Org.
Chem. 2005, 4891.
29) Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic
Synthesis, 3rd ed.; Wiley: New York, 1999, 329–347.
30) Wilson, G. E. Jr.; Huang, M. G.; Schloman, W. W. Jr. J. Org.
Chem. 1968, 33, 2133.
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