Protection and deprotection of acetals by using MoO3/SiO 2

Article abstract of DOI:10.1080/15459620500408868

Acetalization of aldehydes using a new silica-supported molybdenum(VI) oxide (20%) catalyst has been explored. Additionally, facile deprotection strategy for the acetals is reported including the results from the replacement of solvent studies. The protocol achieved the protection O,O-acetals in excellent yield within a few hours under neutral conditions and also deprotection of aromatic O,O-acetals in excellent yields was achieved within a few minutes in aqueous acetone. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15459620500408868

This article was downloaded by: [University of Memphis]
On: 03 September 2012, At: 05:43
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
Synthetic Communications: An International
Journal for Rapid Communication of
Synthetic Organic Chemistry
Publication details, including instructions for authors and subscription
information:
http://www.tandfonline.com/loi/lsyc20
Protection and Deprotection of Acetals by
Using MoO3/SiO2
Rajesh S. Bhosale a , Sidhanath V. Bhosale b , Sheshanath V. Bhosale b
,
Kuldeep S. Solanke c , Rajendra P. Pawar c , Harish S. Chougule d & Mohan K.
Dongare d
a School of Chemical Sciences, Swami Ramanand Teerth Marthwada
University, Nanded, India
b Institute of Chemistry—Organic Chemistry, Freie University, Berlin,
Germany
c Organic Chemistry Synthesis Lab., Dnyanopasak College, Parbhani, India
d Catalysis Division, National Chemical Laboratory, Pune, India
Version of record first published: 16 Aug 2006
To cite this article: Rajesh S. Bhosale, Sidhanath V. Bhosale, Sheshanath V. Bhosale, Kuldeep S. Solanke,
Rajendra P. Pawar, Harish S. Chougule & Mohan K. Dongare (2006): Protection and Deprotection of Acetals by
Using MoO3/SiO2 , Synthetic Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 36:5, 659-663
To link to this article: http://dx.doi.org/10.1080/15459620500408868
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
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.
The publisher does not give any warranty express or implied or make any representation that the
contents will be complete or accurate or up to date. The accuracy of any instructions, formulae,
and drug doses should be independently verified with primary sources. The publisher shall not
be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or
howsoever caused arising directly or indirectly in connection with or arising out of the use of this
material.

Synthetic Communicationsw, 36: 659–663, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/15459620500408868
Protection and Deprotection of Acetals by
Using MoO3/SiO2
Rajesh S. Bhosale
School of Chemical Sciences, Swami Ramanand Teerth Marthwada
University, Nanded, India
Sidhanath V. Bhosale and Sheshanath V. Bhosale
Institute of Chemistry—Organic Chemistry, Freie University, Berlin,
Germany
Kuldeep S. Solanke and Rajendra P. Pawar
Organic Chemistry Synthesis Lab., Dnyanopasak College,
Parbhani, India
Harish S. Chougule and Mohan K. Dongare
Catalysis Division, National Chemical Laboratory, Pune, India
Abstract: Acetalization of aldehydes using a new silica-supported molybdenum(VI)
oxide (20%) catalyst has been explored. Additionally, facile deprotection strategy
for the acetals is reported including the results from the replacement of solvent
studies. The protocol achieved the protection O,O-acetals in excellent yield within a
few hours under neutral conditions and also deprotection of aromatic O,O-acetals in
excellent yields was achieved within a few minutes in aqueous acetone.
Keywords: Acetals, protection, deprotection, MoO3/SiO2
A number of useful and reliable acetalization methods catalyzed by a variety
of Lewis acids,[1,2] TMSCl,[3] BuSnCl3,[4] TsOH,[5] bis-trimethylsilyl ether of
Received in India August 3, 2005
Address correspondence to Rajesh S. Bhosale, School of Chemical Sciences,
Swami Ramanand Teerth Marthwada University, Nanded 431 606, India. E-mail:
rsbhosale03@yahoo.co.in
659

660
R. S. Bhosale et al.
Scheme 1.
ethane1,2-diol and trimethylsilyl triflate,[6] AlFe-pillared montmorillonite,[7]
CdI2,[8] titanium cation-exchanged montmorillonite,[9] TMSOTf,[10]
Bi(NO3)3,[11] polymer-bound metal complexes,[12] and so forth have been
reported in the literature.
A literature survey reveals that molybdenum oxide without support or
supported on SiO2 or Al2 O3 is a useful solid catalyst for various reactions
(e.g., oxidation of ammonia to elemental N2,[13] Beckman rearrangement,[14]
esterification,[15] transesterification,[16] nitration of fluorotoluene using nitric
acid,[17] and the synthesis of diphenyl carbonate[15]). MoO3/SiO2
(Scheme 1) is explored as a new and efficient catalyst for the acetalization
of carbonyl compounds, giving the corresponding acetals in excellent yields
(Table 1). The reaction of benzaldehyde with ethylene glycol in the
presence of MoO3/SiO2 in dry toluene at 1108C was completed in 2 h to
provide the acetal (entry l).
We have also observed that MoO3/SiO2 in the presence of aqueous
acetone is effective to carry out the deprotection of acetals derivatives in
90–98% yields (Scheme 2). To determine the scope and chemoselectivity
of the reaction, different acetals (Table 2) were deprotected in excellent yields.
EXPERIMENTAL SECTION
Procedure for the preparation of catalyst,14 MoO3/SiO2 catalyst was prepared
.
by the sol-gel method using ammonium molybdate [(NH4)6 Mo7 O24 4H2 O]
and ethyl silicate-40 followed by drying and calcinations at 5008C. The
catalyst was characterized for structural characterization by atomic absorption
spectroscopy and X-ray diffraction analysis. Chemical analysis of MoO3/SiO2
showed the composition of the catalyst as 19.5 mol% MoO3 and 80.5 mol%
SiO2. The detailed characterization of MoO3/SiO2 with XRD pattern and
TPD analysis was already reported by us.
General procedure for acetalization, A mixture of aldehyde (10 mmol),
ethane-1,2-diol (20 mmol) and MoO3/SiO2 (100 mg) in toluene (20 mL)
was heated at 1108C. The progress of the reaction monitored by TLC. After
completion of the reaction (2–2.5 h), the catalyst was filtered, the filtrate

Protection and Deprotection of Acetals
661
Table 1. Acetalization of aldehydes using MoO3/SiO2 as a catalysta
Entry
Substrate 1
Product 3
Time (h)
2
Yield (%)b
1
2
3
4
5
3a
3b
3c
3d
3e
96
94
93
91
90
2.3
2.1
2.4
2.5
6
7
3f
2.1
2.2
95
93
3g
8
3h
3i
2.4
2.2
2.1
92
93
94
9
10
3j
aAll the products were characterized by 1H NMR, identified with authentic samples.
bIsolated yield.
Scheme 2.

662
R. S. Bhosale et al.
Table 2. Mild deprotection of acetals using MoO3/Sio2 as catalysta
Entry
1
Substrate 1
Product 2
Time (min)
40
Yield (%)b
98
2a
2
3
4
5
2b
2c
2d
2e
42
55
54
60
95
93
91
94
6
7
2f
45
56
95
93
2g
8
2h
2i
53
51
55
95
97
95
9
10
2j
aAll the products were characterized by 1H NMR identified with authentic samples.
bIsolated yield.

Protection and Deprotection of Acetals
663
concentrated under reduced pressure and chromatographed on SiO2 (1:5
chloroform:pet ether) to afford the pure acetals in excellent yields.
General procedure for hydrolysis of acetals, A mixture of acetal
(10 mmol) and the catalyst (100 mg) in water: acetone mixture (3:10,
20 mL) was refluxed with stirring. The progress of the reaction was
monitored by TLC with authentic samples. After completion of the reaction
(40–60 min), the catalyst was filtered and recovered, and filtrate was
extracted with chloroform (3 Â 20 mL). The organic layer was dried
(anhydrous Na2 SO4) and concentrated to give the corresponding aldehydes
in excellent yields.
REFERENCES
1. Schwenk, E.; Fleischer, G.; Whitman, B. J. Am. Chem. Soc. 1938, 60, 1702–1703.
2. Mackinzie, C. A.; Stocker, J. H. J. Org. Chem. 1955, 20, 1695–1701.
3. Chan, T. H.; Brook, M. A.; Chaly, T. Synthesis 1983, 203.
4. Daniele, M.; Giuseppe, T. Main Group Met. Chem. 1990, 363.
5. Lu, T.; Yang, J.; Sheu, L. J. Org. Chem. 1995, 60, 2931–2934.
6. (a) Tsunoda, T.; Suzuki, M.; Noyori, R. Tetrahedron Lett. 1980, 21, 1357;
(b) Kim, S.; Kim, Y. G.; Kim, D. Tetrahedron Lett. 1992, 33, 2565;
(c) Lillie, B. M.; Avery, M. A. Tetrahedron Lett. 1994, 35, 969.
7. Cramarossa, M. R.; Forti, L.; Guelfi, F. Tetrahedron. 1997, 53, 15889.
8. Laskar, D. D.; Prajapati, D.; Sandhu, J. S. Chem. Lett. 1999, 1283–1284.
9. Tomonori, K.; Tomoo, M.; Kohki, E.; Kiyotomi, K. Tetrahedron Lett. 2001,
42 (47), 8329–8332.
10. Kasaaki, K.; Wataru, H. J. Org. Chem. 2003, 68 (9), 3413–3415.
11. Srivastava, N.; Dasgupta, S. K.; Banik, B. K. Tetrahedron Lett. 2001, 42 (47),
8329–8332.
12. Shun-Jun, J.; Lin, W. J. Mol. Catal. 2003, 202 (1–2), 41–46.
13. (a) Lietti, L.; Ramis, G.; Busca, G.; Bregani, F.; Forzatti, P. Catal. Today. 2000,
61, 187–195; (b) Biermann, J. J.P.; Janseen, F. J.J.G.; De Boer, M.; Van
Dillen, A. J.; Geus, J. W.; Vogt, E. T. C. J. Mol. Catal. 1990, 60, 229–238.
14. Dongare, M. K.; Bhagwat, V. V.; Ramana, C. V.; Gurjar, M. K. Tetrahedron Lett.
2004, 45, 4759–4762.
15. Ono, Y.; Fu, Z. H. J. Mol. Catal. 1997, 118, 293–299.
16. Madje, B. R.; Patil, O. T.; Shindalkar, S. S.; Benjamin, S. B.; Shingare, M. S.;
Dongare, M. K. Catal. Commun. 2004, 5 (7), 353–357.
17. Maurya, S. K.; Gurjar, M. K.; Malshe, K. M.; Patil, P. T.; Dongare, M. K.;
Kemnitz, E. Green Chem. 2003, 5 (6), 720–723.