An efficient one-pot conversion of THP and TMS ethers to sulfonate esters using FeCl3-montmorillonite K-10 clay

Article abstract of DOI:10.1515/znb-2005-0711

Various tetrahydropyranyl and trimethylsilyl ethers are efficiently transformed into the corresponding sulfonate esters with sulfonyl chlorides in the presence of FeCl₃-Montmorillonite K-10 clay.

Full text of DOI:10.1515/znb-2005-0711

An Efficient One-Pot Conversion of THP- and TMS Ethers to Sulfonate
Esters Using FeCl3-Montmorillonite K-10 Clay
Barahman Movassagha and Salman Shokri
Department of Chemistry, K. N. Toosi University of Technology, P. O. Box 16315-1618, Tehran, Iran
a Kermanshah Oil Refining Company, Kermanshah, Iran
Reprint requests to Dr. B. Movassagh. E-mail: bmovass1178@yahoo.com
Z. Naturforsch. 60b, 763 – 765 (2005); received March 29, 2005
Various tetrahydropyranyl and trimethylsilyl ethers are efficiently transformed into the correspond-
ing sulfonate esters with sulfonyl chlorides in the presence of FeCl3-Montmorillonite K-10 clay.
Key words: Sulfonate Esters, FeCl3-Montmorillonite K-10, Trimethylsilyl Ethers,
Tetrahydropyranyl Ethers, Clay Catalyst
Sulfonate esters are especially useful substrates in sions of THP and TMS ethers into the correspond-
nucleophilic substitution reactions used in synthesis. ing carboxylic esters in the presence of Montmoril-
Their preparation from alcohols is an effective way lonite K-10 clay [7, 8]. In continuation of our ongo-
of installing a reactive leaving group, e.g. on an alkyl ing program to develop environmentally benign meth-
chain. p-Toluenesulfonate- and methanesulfonate es- ods using supported reagents, this article describes
ters are the most frequently used groups for preparative a new, simple, and efficient one-pot protocol for the
work. The usual method for preparation of sulfonates deprotection-sulfonylation of THP and TMS ethers
relies on the use of the corresponding sulfonyl chlo- with sulfonyl chlorides in refluxing acetonitrile using
ride or anhydride in the presence of triethylamine [1], FeCl3 impregnated Montmorillonite K-10 as a mild
pyridine [2], 1,4-diazabicyclo[2.2.2]octane (DABCO) and non-corrosive solid catalyst (Scheme 1). The focal
[3] or aqueous base in a Schotten-Baumann type re- point of this report is on the transformations of O-C
action. An alternative for preparing tosylates and me- and O-Si bonds into O-SO2 bonds.
sylates is to convert the alcohol into its lithium salt,
which is then allowed to react with the sulfonyl chlo-
ride [4]. Sulfonic acids are also used for the synthe-
FeCl −Mont.K10
3
RO-THP
RO-TMS
+ R’SO2Cl −−−−−−−−−−→ ROSO2R’
CH CN, reflux
3
sis of sulfonate esters but expensive alkylating agents Scheme 1.
such as trialkyl orthoformate, alkyl ethers, esters or 2-
alkoxybenzothiazolium salts are employed instead of
alcohol [5]. To the best of our knowledge, direct con-
version of tetrahydropyranyl (THP) and trimethylsilyl
(TMS) ethers into the corresponding sulfonate esters
have not been reported in the literature.
The catalyst used here can easily be prepared [9]
from readily available and inexpensive FeCl3 and
Montmorillonite K-10 clay in dry acetonitrile. In or-
der to have a background knowledge of the activ-
ity of the extensively used Montmorillonite clays, n-
butylOTHP was treated with TsCl using different clays
(Table 1). It was found that FeCl3 supported Mont-
morillonite K-10 is most effective among the clays
Results and Discussion
Heterogeneous reactions that are facilitated by sup- for the deprotection-sulfonylation of THP ethers. The
ported reagents on various solid surfaces have received iron content of the clay determined by the atomic ab-
attention in recent years [6]. The advantage of these sorption technique was 0.15 mmol/g of solid catalyst.
methods over conventional homogeneous reactions is Using n-butylOTHP, the amount of catalyst was opti-
that they provide greater selectivity, enhanced reac- mized and an ether to clay ratio of 1 : 0.038 was taken.
tion rates, cleaner products, and simplicity of handling. The catalyst◦can be recovered and reused after activa-
Previously, we have developed several direct conver- tion at 280 C. In this study, different aliphatic THP
c
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764
B. Movassagh – S. Shokri · An Efficient One-Pot Conversion of THP- and TMS Ethers
Table 1. Deprotection-sulfonylation of n-butylOTHP using
various clay catalysts.
fonate esters prepared from methanesulfonyl chloride
(entries 11 – 13, Table 2, and entries 10 – 12, Table 3)
need shorter reaction times and generally give higher
yields than those produced from arylsulfonyl chlorides.
Clay catalyst
Time (h)
Yielda (%)
Montmorillonite K-10
Montmorillonite KSF
Fe3+-Montmorillonite K-10
FeCl3-Montmorillonite K-10
24
24
24
7
25
20
57
81
Conclusion
a
Isolated yields.
A simple, and efficient method has been developed
for one-step deprotection-sulfonylationof a wide range
of THP and TMS ethers by using an inexpensive, non-
hazardous, and easily available catalyst. The present
protocol has the additional advantages of easy work-
up and high yield.
Table 2. Preparation of sulfonate esters from THP ethers us-
ing FeCl3-Mont. K-10.
Entry
THP
ether
Sulfonyl
chloride
Time Yielda Ref.b
(h) (%)
1
CH3CH2OTHP
p-CH3C6H4SO2Cl
6
7
7
7
8
8
75 [10]
81 [11]
79 [10]
2 CH3(CH2)2CH2OTHP p-CH3C6H4SO2Cl
3 CH3(CH2)3CH2OTHP p-CH3C6H4SO2Cl
4 CH3(CH2)6CH2OTHP p-CH3C6H4SO2Cl
5
6
7
8
9
80
[1]
Experimental Section
PhCH2OTHP
CH2=CHCH2OTHP p-CH3C6H4SO2Cl
CyclohexylOTHP p-CH3C6H4SO2Cl 11
(CH3)2CHOTHP p-CH3C6H4SO2Cl 10
D,L-CH3(CH2)5- p-CH3C6H4SO2Cl 11
CH(CH3)OTHP
p-CH3C6H4SO2Cl
70 [12]
72 [10]
78 [10]
70 [10]
68 [10]
FeCl3-Montmorillonite K-10 catalyst was prepared ac-
cording to the method reported by Laszlo et al. [9]. All prod-
ucts were characterized by comparison of their spectroscopic
data with those of known samples. IR spectra were obtained
using a Shimadzu 470 instrument. 1H NMR spectra were de-
termined by a Bruker AQS Avance 300 MHz spectrometer.
10
11
CyclohexylOTHP
CyclohexylOTHP
C6H5SO2Cl
CH3SO2Cl
CH3SO2Cl
CH3SO2Cl
8
3
2
2
77 [10]
88 [10]
86 [11]
83 [13]
12 CH3(CH2)2CH2OTHP
13 CH3CH2CH2OTHP
General procedure for the conversion of THP ethers into
their corresponding sulfonate esters
a
Yields refer to pure isolated products characterized by IR and
1H NMR spectroscopy; b references for known compounds.
To a stirred suspension of the THP ether (1.0 mmol),
dry acetonitrile (6 ml), and FeCl3-Montmorillonite K-10
(250 mg, containing 0.038 mmol of FeCl3), the sulfonyl
chloride (1.0 mmol) was added. The reaction mixture was
heated at reflux for the time specified in Table 2. Progress
of the reaction was monitored by TLC; on completion, after
cooling, the catalyst was removed by filtration and the filtrate
was evaporated. The resulting crude product was purified
and isolated by preparative TLC (silica gel, eluent petroleum
ether : ethyl acetate = 50 : 1) to afford the desired ester.
Table 3. Preparation of sulfonate esters from TMS ethers us-
ing FeCl3-Mont. K-10.
a
Entry
TMS ether
Sulfonyl chloride Time Yield
(h) (%)
1
2
3
4
5
6
7
8
9
CH3(CH2)2CH2OTMS p-CH3C6H4SO2Cl
CH3(CH2)3CH2OTMS p-CH3C6H4SO2Cl
CH3(CH2)6CH2OTMS p-CH3C6H4SO2Cl
5
6
6
7
6
78
75
80
72
75
80
77
71
82
87
85
85
PhCH2OTMS
CH2=CHCH2OTMS
CyclohexylOTMS
(CH3)2CHOTMS
p-CH3C6H4SO2Cl
p-CH3C6H4SO2Cl
p-CH3C6H4SO2Cl 10
p-CH3C6H4SO2Cl
9
CH3(CH2)5CH(CH3)OTMS p-CH3C6H4SO2Cl 11
General procedure for the conversion of TMS ethers into
their corresponding sulfonate esters
CyclohexylOTMS
CyclohexylOTMS
CH3(CH2)2CH2OTMS
CH3CH2CH2OTMS
C6H5SO2Cl
CH3SO2Cl
CH3SO2Cl
CH3SO2Cl
7
3
3
3
10
11
12
To a solution of the TMS ether (1.0 mmol) in dry ace-
tonitrile (6 ml) was added FeCl3-Montmorillonite K-10 clay
(250 mg, containing 0.038 mmol of FeCl3). The mixture was
refluxed for the appropriate time (Table 3) and cooled. Af-
ter filtration, the filtrate was concentrated and the product
purified and isolated by preparative TLC (silica gel, eluent
petroleum ether : EtOAc = 50 : 1).
a
Isolated yields.
ethers were treated with p-toluenesulfonyl, benzene-
sulfonyl, and methanesulfonyl chloride in the presence
of the catalyst in refluxing acetonitrile to obtain the
corresponding sulfonate esters in good to high yields
(Table 2). The catalyst, FeCl3-Mont. K-10 clay, is also
efficient for the preparation of sulfonate esters from
TMS ethers (Table 3). It is worth noting that in both
reactions carbon-carbon double bonds remains unaf-
Acknowledgements
The authors thank K. N. Toosi University of Technology
Research Council and Kermanshah Oil Refining Company
fected (entry 6, Table 2, and entry 5, Table 3). Sul- for financial assistance.
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B. Movassagh – S. Shokri · An Efficient One-Pot Conversion of THP- and TMS Ethers
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