Quinolinium fluorochromate: An efficient and convenient reagent for oxidative cleavage of thioacetals to their parent carbonyl compounds

Article abstract of DOI:10.1080/104265090930326

Deprotection of thioacetals to their parent carbonyl compounds in high yields has been carried out using quinolinium fluorochromate under mild conditions. Copyright Taylor & Francis Inc.

Full text of DOI:10.1080/104265090930326

This article was downloaded by: [University of Tennessee, Knoxville]
On: 03 January 2015, At: 00:19
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
Quinolinium Fluorochromate:
An Efficient and Convenient
Reagent for Oxidative Cleavage
of Thioacetals to Their Parent
Carbonyl Compounds
Mahmood Tajbakhsh a , Kamal Alimohammadi a ,
Farhad Ramzanian-Lehmali a , Mohamad Barghamadi
b & Alireza Shakeri c
a University of Mazandaran , Babolsar, Iran
b Islamic Azad University of Sabzevar , Sabzevar, Iran
c University of Gorgan , Gorgan, Iran
Published online: 16 Aug 2006.
To cite this article: Mahmood Tajbakhsh , Kamal Alimohammadi , Farhad Ramzanian-
Lehmali , Mohamad Barghamadi & Alireza Shakeri (2005) Quinolinium Fluorochromate:
An Efficient and Convenient Reagent for Oxidative Cleavage of Thioacetals to
Their Parent Carbonyl Compounds, Phosphorus, Sulfur, and Silicon and the Related
Elements, 180:11, 2587-2591, DOI: 10.1080/104265090930326
To link to this article: http://dx.doi.org/10.1080/104265090930326
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, 180:2587–2591, 2005
Copyright © Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/104265090930326
Quinolinium Fluorochromate: An Efficient and
Convenient Reagent for Oxidative Cleavage of
Thioacetals to Their Parent Carbonyl Compounds
Mahmood Tajbakhsh
Kamal Alimohammadi
Farhad Ramzanian-Lehmali
University of Mazandaran, Babolsar, Iran
Mohamad Barghamadi
Islamic Azad University of Sabzevar, Sabzevar, Iran
Alireza Shakeri
University of Gorgan, Gorgan, Iran
Deprotection of thioacetals to their parent carbonyl compounds in high yields has
been carried out using quinolinium fluorochromate under mild conditions.
Keywords Aldehydes; deprotection; ketones; thioacetals; quinolinium fluorochromate
INTRODUCTION
Thioacetals are used frequently to protect carbonyl compounds in the
course of the total synthesis of organic compounds, and hence sev-
eral reagents have been developed for their deprotection.1,2 Despite the
availability of many reagents and procedures for deprotection into their
parent carbonyl compounds, most reagants are usually not straightfor-
ward. Therefore, considerable efforts have been directed towards de-
veloping mild and selective methods for thioacetal deprotection. Typ-
ically, most of these methods require the use of protic or lewis acids
and a large number of these methods require drastic conditions or toxic
reagents such as mercuric3 and Fe (III) reagents or heavy metal salts.4
Received October 14, 2004; accepted December 7, 2004.
We are thankful to the Mazandaran University Research Council for partial support
of this work.
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
2587

2588
M. Tajbakhsh et al.
Thioacetals also have been deprotected by the combined use of molecu-
lar oxygen and catalytic amounts of Bi(NO3)3.5H2O.5 Recently, some
nonmetallic reagents, such as trimethyloxonium tetrafluoroborate,6
methylfluorosulphonate,7 and oxides of nitrogen,8 also have been used
for deprotection. Usually, these methods are expensive and require mul-
tistep operations.
RESULTS AND DISCUSSION
Herein we wish to report an extremely mild method for the deprotection
of thioacetals to the corresponding carbonyl compounds with Quinolin-
ium Fluorochromate (QFC, Scheme 1). This reagent recently has been
used for the oxidation of alcohols,9 the deprotection of trimethylsilyl
ethers,10 the oxidative cleavage of oximes and phenylhydrazones,11 the
conversion of thioamides and thioureas to their oxygen analogues,12
and the oxidation of thiols to disulfides,13 and it has certain advan-
tages over similar oxidizing agents. The results obtained with QFC are
satisfactory and suggest that this new reagent is a valuable addition to
the existing oxidizing agents.
SCHEME 1
Our experiments show that thioacetals are converted to their corre-
sponding aldehydes and ketones in a suitable solvent. Further oxidation
of aldehydes to their carboxylic acids are not observed. Furthermore,
functional groups, such as chloro, boromo, methoxy, nitro, and alkyl,
also were inert to this reagent and no byproduct formation was ob-
served (Table I).
The effect of solvent in the oxidation reaction was evaluated by car-
rying out the oxidation in a series of solvents with varying polarity.
Deprotection of 2-chlorobenzaldehyde thioacetal with QFC in a 1:2.5
ratio was carried out in dichloromethane, chloroform, tetrahydrofuran,
cyclohexan, dioxane, and acetonitril at reflux temperature. The results
are presented in Table II. As indicated in this table, acetonitril was
found to be the best choice for this transformation. This probably is due
to greater solubility of the reagent in this solvent.

Quinolinium Fluorochromate
2589
TABLE I Oxidative Deprotection of Thioacetals With
QFC in CH3CN at Reflux Temperature
Time
(h)
Yieldsa
%
Entry
1
Substance
Product
4.5
90
2
3
4
92
85
4.5
4
5
3.5
2.5
92
87
6
7
2
4
95
91
8
9
3
94
93
2.5
10
4
91
(Continued on next page)

2590
M. Tajbakhsh et al.
TABLE I Oxidative Deprotection of Thioacetals With
QFC in CH3CN at Reflux Temperature (Continued)
Time
(h)
Yieldsa
%
Entry
11
Substance
Product
3.5
94
12
2.5
95
13
14
4
4
90
85
15
4
88
aYields refer to isolated products.
In conclusion, we have developed a mild method for the regeneration
of carbonyl compounds from thioacetal that possess significant advan-
tages over the existing methods, such as having simple procedure, a
high yield, and mild conditions.
EXPERIMENTAL
Products were isolated and their physical data were compared with
those of known samples. Solvent was freshly distilled. Thioacetals14
and QFC10 were prepared according to the described procedures.
TABLE II Oxidative Deprotection of
2-Chlorobenzaldehyde Thioacetal in Diffrent Solvents
Using QFC at a Reflux Temperature
Entry
Solvent
Reaction Period (h)
Yields(%)a
1
2
3
4
5
6
CH2Cl2
CHCl3
THF
c-C6H12
Dioxane
CH3CN
3
4
3
4
5
4
15
20
10
5
30
92
aYields refer to isolated products.

Quinolinium Fluorochromate
2591
General Procedure for the Regeneration of Carbonyl
Compounds from Thioacetals
Thioacetal (1 mmol) was added to a stirred suspension of QFC (0.622 g,
2.5 mmols) in acetonitril (15 mL). The reaction mixture was stirred
at reflux temperature for 2–4.5 h. The progress of the reaction was
monitored by TLC (eluent: CH2Cl2/CCl4, 1:1). After completion of the
reaction, the mixture was filtered and the solid material was washed
with diethylether. The combined filtrate was evaporated under reduced
pressure to give almost pure products in a 85–95% yield (Table I). If
necessary, the products were purified further on a silica-gel plate or
silica-jel column with an appropriate eluent.
REFERENCES
[1] (a) T. W. Greene and P. G. M. Wuts, Protective Groups in Organic Synthesis, 2nd ed.
(John Wiley, New York, 1991); (b) J. R. Hanson, Protecting Groups in Organic Syn-
thesis, 1st ed (Blackwell Science, Malden, MA, 1999); (c) P. J. Kocienski, Protecting
Groups, 1st ed (George Thieme Verlag, Stuttgart, 1994).
[2] (a) p-TsOH/aceton: E. W. Colvin, R. A. Raphael, and J. S. Roberts, J. Chem. Com-
mun., 858 (1971); (b) Amberlyst-15/aqueous acetone: G. M. Coppola, Synthesis, 1,
1021 (1984); (c) 50% Trifluoroacetic acid in CHCl3-H2O: R. A. Ellision, E. R. Luken-
bach, and C. W. Chiu, Tetrahedron Lett., 499 (1975); (d)Aqueous DMSO: T. Kametani,
H. Kondoh, T. Honda, Y. Suzuki, and W. Mori, Chem. Lett., 901 (1989); (e) LiBF4: B.
H. Lipshutz and D. F. Harvey, Synth. Commun., 12, 267 (1982).
[3] (a) L. F. Fieser and M. Fieser, Reagents for Organic Synthesis (John Wiley and Sons,
New York, 1967); (b) E. J. Corey and B. W. Erickson, J. Org. Chem., 36, 3553 (1971).
[4] (a) E. Vedejs and P. L. Fuchs, J. Org. Chem., 36, 366 (1971); (b) T. L. Ho, H. C. Ho, and
C. M. Wong, J. Chem. Soc. Chem. Commun., 791 (1972); (c) A. Hirano, K. Ukawa, S.
Yakabe, J. H. Clarc, and T. Morimoto, Synthesis, 858 (1997); (d) M. Schmittel and
M. Levis, Synlett., 315 (1996).
[5] N. Komatsu, A. Taniguchi, M. Uda, and H. Suzoki, Chem. Commun., 15, 1847 (1996).
[6] T. Oishi, K. Kamemoto, and Y. Ban, Tetrahedron Lett., 13, 1085 (1972).
[7] M. Fetizon and M. Jurion, J. Chem. Soc. Chem. Commun., 382 (1972).
[8] G. Mehta and R. Uma, Tetrahedron Lett., 37, 1897 (1996).
[9] V. Murugesan and A.Podrurangan, Ind. J. Chem., 31B, 377 (1992).
[10] M. Tajbakhskh, I. Mohammadpoor-Baltork, and F. Ramzanian-Lehmali, Phospho-
rus, Sulfur, and Silicon, 178, 2617 (2003).
[11] M. Tajbakhsh, I. Mohammadpoor-Baltork, and F. Ramzanian-Lehmali, J. Chem.
Research (S), 710 (2003).
[12] M. Tajbakhsh, I. Mohammadpoor-Baltork, and S. K. Alimohammadi, Ind. J. Chem.,
42B, 2638 (2003).
[13] M. Tajbakhsh, I. Mohammadpoor-Baltork, and K. Alimohammadi, Monatsh. Chem.,
134, 1571 (2003).
[14] V. Kumar and S. Dev, Tetrahedron Lett., 24, 1289 (1983).