The use of Nafion-H as an efficient catalyst for the direct conversion of primary and secondary trimethylsilyl ethers to their corresponding ethers under mild and heterogeneous conditions

Article abstract of DOI:10.1016/j.tetlet.2003.09.036

Primary and secondary trimethylsilyl ethers were converted to their corresponding ethers in the presence Nafion-H with good to excellent yields under mild and heterogeneous conditions.

Full text of DOI:10.1016/j.tetlet.2003.09.036

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 8165–8167
The use of Nafion-H® as an efficient catalyst for the direct
conversion of primary and secondary trimethylsilyl ethers to
their corresponding ethers under mild and heterogeneous
conditions
Mohammad Ali Zolfigol,a,* Iraj Mohammadpoor-Baltork,b Davood Habibi,a BiBi Fatemeh Mirjalilic
and Abdolhamid Bamoniria
aChemistry Department, College of Science, Bu-Ali Sina University, Hamadan, Zip Code 65174, Iran
bDepartment of Chemistry, Isfahan University, Isfahan, Iran
cDepartment of Chemistry, College of Science, Yazd University, Yazd, Iran
Received 1 July 2003; revised 13 August 2003; accepted 3 September 2003
Abstract—Primary and secondary trimethylsilyl ethers were converted to their corresponding ethers in the presence Nafion-H®
with good to excellent yields under mild and heterogeneous conditions.
© 2003 Elsevier Ltd. All rights reserved.
Symmetrical and unsymmetrical alkyl/aryl ether forma-
tion is an important reaction in organic synthesis and
has generated significant interest in recent years.1–18
Methods to effect this transformation include the clas-
sic Williamson procedure, the Mitsunobu reaction, and
the Ullmann condensation. Ion-exchange resin and het-
eroploy acid catalyzed etherification have also been
reported.15–18 Rearrangement and elimination of alkyl
alcohols that are sterically hindered is the major disad-
vantage of the older procedures for ether synthesis.
This problem is amplified when the alcohols are immo-
bilized on solid supports and the activated species
becomes the limiting reagent.4 The alcohol–sulfuric acid
reaction is most often used for the conversion of simple
primary alcohols into symmetrical ethers. Secondary
and tertiary alcohols undergo predominantly dehydra-
tion when subjected to these conditions. Occasionally a
small amount of the symmetrical ether is formed as a
by-product in the case of secondary alcohols.19 In 1987,
Olah’s group reported a facile procedure for the synthe-
sis of symmetrical and unsymmetrical ethers via reduc-
tive coupling of carbonyl compounds under mild
acid-free conditions.20
On the other hand, acids are widely used as catalysts in
industry producing more than 1×108 mt/year of prod-
ucts. The most commonly used acids are HF, H2SO4,
HClO4, and H3PO4 (in liquid form or supported on
Kieselguhr). Solid acids have many advantages such as
simplicity in handling, decreased reactor and plant cor-
rosion problems, and environmentally safe dis-
posal.18,21–23 There is a great deal of current research
and general interest in heterogeneous systems24 because
of the importance such systems have in industry and in
developing technologies.25 Among reported solid acids,
Nafion-H® has been used for a wide variety of reactions
ranging from alkylation with olefins, reaction of alkyl
halides and alkyl esters, isomerization, transalkylation,
acylation and nitration reactions and ether and ester
synthesis, acetal formation and rearrangements.26 Very
recently, we have reported the use of Nafion-H® as an
excellent solid acid for the nitrosation of secondary
amines under mild and heterogeneous conditions.27 In
continuation of our studies, we have found that
trimethylsilyl ethers can be converted to the corre-
sponding ethers in the presence Nafion-H®. Therefore,
Keywords: Nafion-H®; trimethylsilyl ethers; ethers; heterogeneous
conditions.
* Corresponding author. Fax: (+98) 811 8272404; e-mail: zolfi@
basu.ac.ir
Scheme 1.
0040-4039/$ - see front matter © 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2003.09.036

8166
M. Ali Zolfigol et al. / Tetrahedron Letters 44 (2003) 8165–8167
Table 1. The direct conversion of primary and secondary trimethylsilyl ethers 1 to the corresponding symmetrical ethers (2)
in the presence of Nafion-H® in n-hexane at room temperaturea
we decided to apply this reagent for ether synthesis.
Here we wish to report the first examples of the direct
conversion of primary and secondary trimethylsilyl
ethers into ethers with good to excellent yields under
mild and heterogeneous conditions (Scheme 1).
A mixture of the substrate 1 (4 mmol), n-hexane (20
ml) and Nafion-H® (1 g) was stirred at room tempera-
ture for the specified time (Table 1).28 The reaction was
monitored by TLC. After completion of the reaction
the mixture was filtered and the solid residue was

M. Ali Zolfigol et al. / Tetrahedron Letters 44 (2003) 8165–8167
8167
washed with n-hexane. Evaporation of the solvent fol-
lowed by column chromatography on silica gel gave
pure ethers in good to excellent yields.
13. Linnekoski, J. A.; Krause, A. O. I.; Holmen, A.; Kjetsa,
M.; Moljord, K. Applied Catalysis A: General 1998, 174,
1.
14. Crombez-Robert, C.; Benazza, M.; Frechou, C.;
Demailly, G. Carbohydr. Res. 1998, 307, 355.
15. Linnekoski, J. A.; Krause, A. O. I.; Struckmann, L. K.
Applied Catalysis A: General 1998, 174, 117.
16. Rihko-Struckmann, L. K.; Latostenmaa, P. V.; Krause,
A. O. J. Mol. Catalysis A: Chemical 2001, 177, 41.
17. Saha, B. React. Funct. Polym. 1999, 40, 51.
18. Yadav, G. D.; Bokade, V. V. Applied Catalysis A: Gen-
eral 1998, 147, 299.
19. Streitwieser, A.; Heathcock, C. H.; Kosower, E. M.
Introduction to Organic Chemistry, 4th edn; Macmillan
Publishing Company, 1992; p. 233.
20. Sassaman, M. B.; Kotian, K. D.; Prakash, G. K. S.;
Olah, G. A. J. Org. Chem. 1987, 4314.
21. Corma, A. Current Opinion in Solid State & Materials
Science. Current Chemistry Ltd 1997, 2, 63–75.
22. Corma, A.; Garcia, H. Catalysis Today 1997, 38, 257.
23. Sikdar, S. K.; Howell, S. G. J. Cleaner Prod. 1998, 6, 253.
24. (a) Zolfigol, M. A.; Torabi, M.; Mallakpour, S. E. Tetra-
hedron 2001, 57, 8381 and other references cited therein;
(b) Shirini, F.; Zolfigol, M. A.; Mallakpour, B.; Mallak-
pour, S. E.; Hagipour, A. Tetrahedron Lett. 2002, 43,
1555; (c) Zolfigol, M. A.; Ghorbani-Choghamarani, A.;
Hazarkhani, H. Synlett 2002, 1002; (d) Salehi, P.; Dabiri,
M.; Zolfigol, M. A.; Bodaghi-fard, M. A. Tetrahedron
Lett. 2003, 44, 2889; (e) Zolfigol, M. A.; Shirini, F.;
Ghorbani-Choghamarani, A.; Mohammadpoor-Baltork,
I. Green Chem. 2002, 4, 562.
In conclusion, Nafion-H® can serve as an efficient
catalyst for the direct conversion of primary (entries
1–22) and secondary (entries 23–25) trimethylsilyl
ethers into the corresponding ethers under mild and
heterogeneous conditions. The yields are good to excel-
lent and the procedure is simple and convenient. Rear-
rangement, elimination and ether cleavage reactions
were not observed. Moreover, reaction is heterogeneous
and may be useful industrially.30
Acknowledgements
Financial support for this work by the research affairs,
Bu-Ali Sina University, Hamadan, Iran, and also Isfa-
han University, Isfahan, Iran (as a common project) is
gratefully acknowledged.
References
1. Quach, T. D.; Batey, R. A. Org. Lett. 2003, 5, 1381.
2. Buck, E.; Song, Z. J.; Tschaen, D.; Dormer, P. G.;
Valante, R. P.; Reider, P. J. Org. Lett. 2002, 4, 1623.
3. Busch-Petersen, J.; Corey, E. J. Org. Lett. 2000, 2, 1641.
4. Xiao, X. Y.; Li, R.; Hurst, D.; Zhuang, H.; Shuhao, S.;
Czarnik, A. W.; Robichaud, A. J.; Wacker, D. A.;
Robertson, D. W. J. Comb. Chem. 2002, 4, 536.
5. Wang, S.; Guin, J. A. Chem. Commun. 2000, 2499.
6. Bagnell, L.; Cablewski, T.; Strauss, C. R. Chem. Com-
mun. 1999, 283.
25. Sheldon, R. A.; Downing, R. S. Applied Catalysis A:
General 1999, 189, 163.
26. Harmer, M. A.; Sun, Q. Applied Catalysis A: General
2001, 221, 45.
27. Zolfigol, M. A.; Habibi, D.; Mirjalili, B. F.; Bamoniri, A.
Tetrahedron Lett. 2003, 44, 3345.
7. Lu, B.; Li, L. J.; Li, T. S.; Li, J. T. J. Chem. Res (S) 1998,
604.
8. Verhoef, M. J.; Creyghton, E. J.; Peters, J. A.; Bekkum,
28. Chemicals were purchased from Fluka, Merck and
Aldrich chemicals companies. The products were charac-
terized by comparison of their spectral (IR, 1H NMR),
TLC and physical data with the authentic samples. All
silyl ethers were synthesized according to the reported
procedure.29
29. Firouzabadi, H.; Karimi, B. Synth. Commun. 1993, 23,
1633.
30. Clark, J. H. Acc. Chem. Res. 2002, 35, 791.
H. V. Chem. Commun. 1997, 1989.
9. Yang, H. M.; Wu, P. I.; Li, C. M. Applied Catalysis A:
General 2000, 193, 129.
10. Liu, J.; Wang, S.; Guin, J. A. Fuel Processing Technol.
2001, 69, 205.
11. Clacens, J. M.; Pouilloux, Y.; Barrault, J. Applied Cataly-
sis A: General 2002, 227, 181.
12. Dong, Y.; Wu, Y.; Wang, J.; Wang, M. European Polym.
J. 2001, 37, 1713.