Efficient and selective oxidative deprotection of trimethylsilyl ethers using supported potassium ferrate under microwave irradiation

Article abstract of DOI:10.1080/10426500307945

Primary and secondary trimethylsilyl ethers are efficiently and rapidly converted to their corresponding carbonyl compounds with supported potassium ferrate under microwave irradiation in solventless system.

Full text of DOI:10.1080/10426500307945

This article was downloaded by: [University of New Mexico]
On: 01 December 2014, At: 06:10
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
Phosphorus, Sulfur, and Silicon and the Related
Elements
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/gpss20
Efficient and Selective Oxidative Deprotection of
Trimethylsilyl Ethers Using Supported Potassium
Ferrate Under Microwave Irradiation
a
b
a
Mahmood Tajbakhsh , Majid. M. Heravi & Setareh Habibzadeh
a
University of Mazandaran , Babolsar, Iran
b
Azzahra University , Tehran, Iran
Published online: 27 Oct 2010.
To cite this article: Mahmood Tajbakhsh , Majid. M. Heravi & Setareh Habibzadeh (2003) Efficient and Selective Oxidative
Deprotection of Trimethylsilyl Ethers Using Supported Potassium Ferrate Under Microwave Irradiation, Phosphorus, Sulfur, and
Silicon and the Related Elements, 178:2, 361-364, DOI: 10.1080/10426500307945
To link to this article: http://dx.doi.org/10.1080/10426500307945
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained
in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the
Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and
should be independently verified with primary sources of information. Taylor and Francis shall not be liable for
any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever
or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of
the Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any
form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://
www.tandfonline.com/page/terms-and-conditions

Phosphorus, Sulfur and Silicon, 2003, Vol. 178:361–364
Copyright �C 2003 Taylor & Francis
1
042-6507/03 $12.00 + .00
DOI: 10.1080/10426500390170525
EFFICIENT AND SELECTIVE OXIDATIVE
DEPROTECTION OF TRIMETHYLSILYL ETHERS
USING SUPPORTED POTASSIUM FERRATE UNDER
MICROWAVE IRRADIATION
a
b
Mahmood Tajbakhsh, Majid. M. Heravi,
and Setareh Habibzadeha
University of Mazandaran, Babolsar, Iran and
Azzahra University, Tehran, Iranb
a
(Received October 19, 2001; accepted March 21, 2002)
Primary and secondary trimethylsilyl ethers are efficiently and rapidly
converted to their corresponding carbonyl compounds with supported
potassium ferrate under microwave irradiation in solventless system.
Keywords: Deprotection; microwave irradiation; oxidation; potassium
ferrate
The trimethylsilyl group is one of the most widely employed protecting
groups in multistep organic synthesis and is often used to prepare silyl
ethers as volatile derivatives of alcohols and phenols.1
Direct oxidation of trimethylsilyl ethers to the corresponding car-
bonyl compounds has found considerable attention during recent years
which exemplifies its significance. Although a large number of reagent
2
are known for such transformation, there still appears a need either
to improve the existing oxidative methods or to introduce new reagents
to permit better selectivity under milder condition, faster reaction and
easier work-up procedure.
Prompted by stringent environment protection laws in recent years,
there has been increasing emphases on the use and design of eco-
friendly reagents, solid and solvent free reactions.3
Application of microwave heating technique is currently under inten-
4
sive examination. Dry media technique has attracted much attention
The authors are thankful to the research council of Mazandaran University for partial
financial support.
Address correspondence to Mahmood Tajbakhsh, Department of Chemistry, School
of Sciences, University of Mazandaran, PO Box 453, Babolsar, Iran. E-mail: tajbaksh@
umz.ac.ir
3
61

3
62
M. Tajbakhsh et al.
recently since organic solvents are expensive and hazardous, and open
5
vessels can be used.
It has been shown that among transition metals, iron is singled
6
out as nontoxic. Association of ferric salt with zeolite had been pio-
neered in our laboratory leading to the design of the “zeofen” as a ver-
7
satile oxidizing reagent. We recently have reported the above reagent
8
for oxidative deprotection of trimethylsilyl ethers. Potassium ferrate
(
K2FeO4) is a sixvalent iron compound which can be easily and eco-
nomically prepared by oxidizing ferric nitrate with sodium hypochlo-
rite and the subsequent treatment with potassium hydroxide. We re-
9
cently have prepared this reagent by an improved method presented
1
0
by Laszlo and his coworker, supported onto montmorillonite k-10 and
11
used that for oxidative deprotection of trimethylsilyl ethers. Although
this oxidative deprotection proceeds efficiently and smoothly, it suffers
from long reaction time (2–11 h). This limitation prompted us to inves-
tigate the advantages of microwave irradiation in solvent-free condi-
tion. In a typical reaction an intimate mixture of potassium ferrate and
benzyltrimethylsilyl ether was irradiated with microwave. Although
oxidative deprotection of benzyltrimethylsilyl ethers is observed, con-
siderable amounts of starting material and some bezylalcohol also are
present.
More seriously, molten potassium ferrate added to the walls of the
vessel making isolation of the products difficult. To circument this prob-
lem, potassium ferrate was supported onto montmorillonite k-10. When
the supported reagent was mixed with bezyltrimethysilyl ether and the
mixture placed in household microwave oven, the reaction was com-
pleted in 2 min in 92% yield. The work-up procedure involves addi-
tion of CH2Cl2, mere filtration, evaporation of the solvent, and passing
the residue through a small pad of silica gel using suitable solvent.
To assess the generality of the method, a variety of trimethylsilyl
ethers were treated likewise to afford the corresponding deshielded
carbonyl compounds in high to excellent yield (Table I). No overoxi-
dation leading to carboxylic acid was observed. Cinnamyltrimethylsilyl
ether was oxidatively deprotected to cinnamaldehyde by this method
showing that the carbon-carbon double bond is not prone to cleavage
by this method. In summary the present procedure for the cleavage
of trimethylsilyl ether has all advantages of using iron salt as eco-
friendly and nontoxic material, selectivity, and easy work-up procedure
due to impregnation of reagents onto mineral supports as well as very
short reaction time without the use of expensive and hazardous organic
solvents.

Efficient and Selective Oxidative Deprotection of Trimethylsilyl Ethers
363
TABLE I Oxidative Deprotection of Trimethylsilyl Ethers with K
Supported on Montmorillonite k-10 under Microwave Irradiation
in Solvent-Free Conditions
2 4
FeO
Substrate
PhCH2OSiMe3
Time (min)
Products
Yield (%)a
2
2
4
5
2
4
5
4
5
PhCHO
95
92
88
82
90
82
81
82
85
4
2
3
3
4
-Me-C6H4CH2OSiMe3
4-Me-C6H4CHO
-NO2-5-MeC6H3CH2SiMe3
-NO2-C6H4CH2OSiMe3
-MeO-C6H4CH2OSiMe3
-Cl-C6H4-CH (OSiMe3)-CH3
2-NO2-5-Me-C6H3CHO
3-NO2-C6H4CHO
3-MeO-C6H4CHO
4-ClC6H4COCH3
Cyclohexanone
c-C6H11OSiMe3
-Me-c-C6H10OSiMe3
-)Mentholtrimethylsilyl ether
2
(
2-Methylcylclohexanone
(-) Menthone
aYields based on isolated product.
Caution: Although we did not have any problems and the above procedure worked
(
safely in our hands, using a microwave oven in an appropriate hood is recommended).
EXPERIMENTAL
Silyl ethers were synthesized from the corresponding hydroxyl
1
2
compounds according to the literature. All products were known and
characterized by comparison of their physical data with those of au-
thentic samples. The reagent was prepared by the impregnation of
potassium ferrate on montmorillonite k-10 which was purchased from
Aldrich Chemical LTD. Thin layer chromatography was done on pre-
coated silica gel.
Oxidative Deprotection of Trimethylsilyl Ethers:
General Procedure
In a typical procedure, trimethylsilyl ethers (2 mmol) is intimately
mixed with potassium ferrate (4 mmol) supported on montmorillonite
k-10. The mixture is transferred into a small beaker, and irradiated
by microwave (National, 900 w operating at a frequency 2450 MHz)
for the indicated time. The progress of reaction was monitored by TLC
(
pet-ether: ethyl acetate, 80:20). After the completion of reaction the
product was extracted with ether and filtered.

3
64
M. Tajbakhsh et al.
Evaporation of solvent gave a crude product which was passed
through a short column of silica gel, using pet-ether: ethyl acetate
(
(
80:20) as an eluent to afford the corresponding carbonyl compound
Table I).
REFERENCES
[
1] (a) E. W. Calvin, Chem. Soc. Rev., 7, 15 (1978); (b) T. W. Greens, Protective Groups in
Organic Synthesis (Wiley, New York, 1991), 2nd ed., p. 68; (c) C. B. Reese, Protective
Groups in Organic Chemistry (Plenum, London, 1973), ch. 3; (d) M. Lalande and
T. H. Chan, Synthesis, 817 (1985).
[
2] (a) I. Mohammadpoor-Baltork and Sh. Pouranshivani, Synthesis, 765 (1997);
(b) R. D. Narcross, P. Vonmatt, H. C. Koll, and D. Bellus, Tetrahedron, 53, 10289
(1997); (c) M. M. Heravi, D. Ajami, and K. Tabar Hydar, Monatsh Chem., 130, 337
(1999); (d) M. M. Heravi, D. Ajami, and M. Ghassemzadeh, Synthesis, 393 (1999);
(e) G. Page and G. W. Loar, Encyclopedia of Chemical Technoloy, edited by Kirk-
Othmer (Wiley, New York, 1998), 4th ed.
[
[
3] C. B. Khouv, C. Partl, J. A. Lalenger, and M. E. Davis, J. Catal., 149, 195 (1994).
4] (a) A. Abramovitch, Org. Prep. Proce. Int., 23, 685 (1991); (b) D. M. P. Mengos and
D. R. Baghusst, Chem. Soc. Rev., 20, 1 (1991); (c) S. Caddick, Tetrahedron, 51, 10403
(1995).
[
5] (a) M. M. Heravi, D. Ajami, M. M. Mojtahedi, and M. Ghassemzadeh, Tetrahe-
dron Lett., 40, 56 (1999); (b) M. M. Heravi, Y. Sh. Beheshtiha, M. Ghassemzadeh,
R. Hekmatshoar, and N. Sarmad, Monatsh Chem., 131, 187 (2000).
[
[
[
[
6] W. A. Kneppor, Encyclopedia of Chemical Technology, edited by Kirk-Othmer
(New York: John Wiley and Sons 1981), 3rd ed., vol. 13, p. 735.
7] (a) M. M. Heravi, D. Ajami, K. Aghapoor, and M. Ghassemzadeh, J. Chem. Soc.
Chem. Commun., 833 (1999).
8] M. M. Heravi, D. Ajami, M. Ghassemzadeh, and K. Tabar Heydar, Synth. Commun.,
3
1(14), 2097–2100, (2001).
9] G. W. Thompson, L. T. Ockerman, and J. M. Schreyer, J. Am. Chem. Soc., 73, 1379
1951).
(
[
[
10] L. Delaude and P. Laszlo, J. Org. Chem., 61, 6300 (1996).
11] M. Tajbakhsh, M. M. Heravi, S. Habibzadeh, and M. Ghassemzadeh, J. Chem. Res.
(S), 30 (2001).
[
12] E. W. Calvin, Chem. Soc. Rev., 7, 15 (1978).