Immediate and efficient oxidative deprotection of dithioacetals to carbonyl compounds by zinc dichromate trihydrate (ZnCr2O7 · 3H2O)

Article abstract of DOI:10.1081/SCC-120037908

Zinc dichromate trihydrate (ZnCr₂O₇ · 3H ₂O) is an efficient oxidizing agent for the immediate deprotection of 1,3-dithianes, 1,3-dithiolanes, and dibutyl dithioacetals to their corresponding carbonyl compounds in non-aqueous and aprotic conditions at room temperature.

Full text of DOI:10.1081/SCC-120037908

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Immediate and Efficient Oxidative Deprotection
of Dithioacetals to Carbonyl Compounds by Zinc
Dichromate Trihydrate (ZnCr2O7 · 3H2O)
Habib Firouzabadi a , Nasser Iranpoor a , Hassan Hassani a & Sara Sobhani a
a Department of Chemistry, College of Sciences , Shiraz University , Shiraz, 71454, Iran
Published online: 20 Aug 2006.
To cite this article: Habib Firouzabadi , Nasser Iranpoor , Hassan Hassani & Sara Sobhani (2004) Immediate and Efficient
Oxidative Deprotection of Dithioacetals to Carbonyl Compounds by Zinc Dichromate Trihydrate (ZnCr2O7 · 3H2O), Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 34:11, 1967-1972,
DOI: 10.1081/SCC-120037908
To link to this article: http://dx.doi.org/10.1081/SCC-120037908
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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 11, pp. 1967–1972, 2004
Immediate and Efficient Oxidative
Deprotection of Dithioacetals to Carbonyl
Compounds by Zinc Dichromate
.
Trihydrate (ZnCr2O7 3H2O)
*
*
Habib Firouzabadi, Nasser Iranpoor, Hassan Hassani,
and Sara Sobhani
Department of Chemistry, College of Sciences, Shiraz University,
Shiraz, Iran
ABSTRACT
.
Zinc dichromate trihydrate (ZnCr2O7 3H2O) is an efficient oxidizing
agent for the immediate deprotection of 1,3-dithianes, 1,3-dithiolanes,
and dibutyl dithioacetals to their corresponding carbonyl compounds in
non-aqueous and aprotic conditions at room temperature.
Key Words: Zinc dichromate trihydrate; Oxidative deprotection; 1,3-
Dithianes; 1,3-Dithiolanes; Dibutyl dithioacetals; Thioacetals; Carbonyl
compounds.
*
Correspondence: Habib Firouzabadi and Nasser Iranpoor, Department of Chemistry,
College of Sciences, Shiraz University, Shiraz 71454, Iran; Fax: þ98-711-2280926;
E-mail: firouzabadi@chem.susc.ac.ir or iranpoor@chem.susc.ac.ir.
1967
DOI: 10.1081/SCC-120037908
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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Firouzabadi et al.
INTRODUCTION
Chemical manipulation of complex polyfunctional molecules often
requires the sequential protection and deprotection of various functionalities.
The electrophilic nature of the carbonyl groups is the dominant nature of their
extensive chemistry. One of the major challenging problems during many
multi-step syntheses is how to protect a carbonyl from nucleophilic attack
until its electrophilic properties can be exploited. For this reason the protection
and deprotection of the carbonyl group remain crucial challenges to organic
chemists. Due to the stability of 1,3-dithioacetals[1] towards various reagents
and reaction conditions and their wide applications as acyl anion equivalents
for carbon–carbon bond forming reactions, 1,3-dithioacetals have attained a
position of prominence in the area of carbonyl group protections.[2] Therefore,
as with most protecting groups, development of new methods for deprotection
of dithioacetals into their corresponding carbonyl compounds have attracted
many attentions.[3] (For a review see Ref.[3j].) Metal coordination, alkylation,
and oxidation are three general strategies which can be used for this purpose.
However, each of the reported procedures suffer from at least one of the
following drawbacks; requiring drastic conditions, multi-step processes,
tedious work-up, long reaction times, low yields, and use of expensive
reagents. Thus, an improved alternative procedure for this important trans-
formation is of practical value and appreciated by synthetic organic chemists.
.
Zinc dichromate trihydrate (ZnCr2O7 3H2O) which is easily prepared
by the reaction of ZnCO3 with CrO3 in an acidic solution is a stable, cheap,
and easily handed compound.[4] Recently, we have reported ZnCr2O7 3H2O
.
as an efficient oxidizing agent for the oxidation of alcohols, oxidative depro-
tection of 1,3-dioxalanes, and oximes to their corresponding carbonyl
compounds and preparation of a-ketophosphonates by the oxidation of
a-hydroxyphosphonates.[5]
.
In this paper, we have applied ZnCr2O7 3H2O as an efficient oxidizing
agent for the immediate deprotection of various types of dithioacetals
to their corresponding carbonyl compounds in non-aqueous and aprotic
conditions at room temperature (Sch. 1).
RESULTS AND DISCUSSION
Oxidative deprotection of 2-phenyl-1,3-dithiolane (1a) as a model com-
pound was studied in several solvents including CH3CN, CH2Cl2, CHCl3,
.
CCl4, and C6H6 using ZnCr2O7 3H2O (2 equiv.) as an oxidant. We found
that CH3CN was a suitable solvent for this purpose. Various types of
aromatic 1,3-dithianes and 1,3-dithiolanes with electron-releasing and

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Deprotection by ZnCr2O7 3H2O
1969
Scheme 1.
electron-withdrawing groups (1a–n), aliphatic 1,3-dithianes and 1,3-dithio-
lanes (1o–q) and dibutyl dithioacetals (1r, s) were cleanly and immediately
deprotected to their corresponding carbonyl compounds in 85–94% yields
.
in CH3CN at room temperature with 2–2.2 equiv. of ZnCr2O7 3H2O (Table 1).
.
In conclusion, we have introduced ZnCr2O7 3H2O as an easily prepared,
cheap, stable oxidant for the fast and high yielding deprotection of various
types of dithioacetals to their corresponding carbonyl compounds. Mild reac-
tion conditions and easy work-up of the reaction mixture are also worthy of
mention for the presented method.
EXPERIMENTAL
.
ZnCr2O7 3H2O and dithioacetals were prepared according to the known
procedures.[1,4] Yields refer to isolated products. The purity determination of
the products were accomplished by TLC on silica gel polygram SIL G/UV
254 plates or GLC on a Shimadzu Model GC-8A instrument with a flame ion-
ization detector and a column of 15% carbowax 20 M/chromosorb-W acid
washed 60–80 mesh. All products were characterized by comparison of
their spectral and physical data with those of authentic samples. Boiling points
of the products were determined under atmospheric pressure unless otherwise
indicated in the table.
General Procedure
To a solution of dithioacetals (1, 1 mmol) in dry CH3CN (5 mL),
.
ZnCr2O7 3H2O (0.67–0.74 g, 2–2.2 mmol) was added. The resulting mixture
was stirred at room temperature. Immediate reaction occurred. Silica gel (1 g)
was added to the reaction mixture and the solvent was evaporated under reduced

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Deprotection by ZnCr2O7 3H2O
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Firouzabadi et al.
pressure. The resulting powder was poured on a silica gel pad (3-cm thick) and
washed with n-hexane/EtOAc (5: 1) (3 ꢀ 30mL). The desired product (2) was
isolated in excellent yields (85–94%) after the evaporation of the solvent.
ACKNOWLEDGMENT
We thank Shiraz University Research Council for the partial support of
this study.
REFERENCES
1. Vogel’s Textbook of Practical Organic Chemistry, 5th Ed.; Longman:
Harlow, 1989; 787.
2. (a) Kociencki, P.J. Protecting Groups; Thieme: New York, 1994;
(b) Corey, E.J.; Seebach, D. Angew. Chem. Int. Ed. Engl. 1965, 4,
1075; (c) Seebach, D. Angew. Chem. Int. Ed. Engl. 1969, 8, 639;
(d) Grobel, B.T.; Seebach, D. Synthesis 1977, 357; (e) Bulman
Page, P.C.; Van Niel, M.B.; Prodger, J.C. Tetrahedron 1989, 45, 7643;
(f) Tietze, L.F.; Weigand, B.; Wulff, C. Synthesis 2000, 69.
3. (a) Greene, T.W.; Wuts, P.G.M. Protective Groups in Organic Synthesis,
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5402; (c) Ho, T.L.; Ho, H.C.; Wong, C.M. J. Chem. Soc. Chem. Commun.
1972, 791; (d) Epling, G.A.; Wang, Q. Tetrahedron Lett. 1992, 33, 5909;
(e) Kamata, M.; Otogawa, H.; Hasegawa, E. Tetrahedron Lett. 1991, 32,
7421; (f) Kamata, M.; Murakami, Y.; Tamagawa, Y.; Kato, M.;
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43, 6031; (j) Banerjee, A.K.; Laya, M.S. Russ. Chem. Rev. 2000, 69, 947.
4. Wolf, S.; Ingold, C.F. J. Am. Chem. Soc. 1983, 105, 7755.
5. (a) Firouzabadi, H.; Sardarian, A.R.; Moosavipour, H.; Afshari, G.M.
Synthesis 1986, 285; (b) Firouzabadi, H.; Iranpoor, N.; Sobhani, S.;
Sardarian, A.R. Tetrahedron Lett. 2001, 42, 4369.
6. Handbook of Table of Organic Compounds Identification, 3rd Ed.; CRC
Press: 1967.
Received in the USA January 6, 2004

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