A fast and efficient deprotection of aldehydes from acylals using a Wells-Dawson heteropolyacid catalyst (H6P2W 18O62 · 24H2O)

Article abstract of DOI:10.1081/SCC-200034783

A rapid and efficient method for the deprotection of aldehyde 1,1-diacetates is described. The reaction was carried out using a Wells-Dawson type catalyst supported on silica. The catalyst, used in 1% molar quantity, is easily recoverable and reusable and maintains the activity after its use in four consecutive reaction batches. The yield of the deprotection was 92-100% (15 examples including nitrobenzaldehyde 1,1-diacetates). Reaction conditions involve short times and the use of toluene as the solvent; isolation is simple and the products are nearly pure.

Full text of DOI:10.1081/SCC-200034783

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A Fast and Efficient
Deprotection of Aldehydes
from Acylals Using a
Wells‐Dawson Heteropolyacid
Catalyst (H6P2W18O62 · 24H2O)
G. P. Romanelli a b , J. C. Autino a , G. Baronetti c
& H. J. Thomas b
a Laboratorio de Estudio de Compuestos Orgánicos
(LADECOR), Departamento de Química, Facultad
de Ciencias Exactas , Universidad Nacional de
La Plata , Calles 47 y 115, B1900AJL, La Plata,
Argentina
b Centro de Investigación y Desarrollo en Ciencias
Aplicadas “Dr. Jorge J. Ronco” (CINDECA),
Departamento de Química, Facultad de
Ciencias Exactas , Universidad Nacional de La
Plata‐CONICET , La Plata, Argentina
c Departamento de Ingeniería Química, Pabellón
de Industrias, Facultad de Ingeniería , Universidad
de Buenos Aires , Buenos Aires, Argentina
Published online: 10 Jan 2011.
To cite this article: G. P. Romanelli , J. C. Autino , G. Baronetti & H. J.
Thomas (2004) A Fast and Efficient Deprotection of Aldehydes from Acylals
Using a Wells‐Dawson Heteropolyacid Catalyst (H6P2W18O62 · 24H2O), Synthetic

Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 34:21, 3909-3914, DOI: 10.1081/SCC-200034783
To link to this article: http://dx.doi.org/10.1081/SCC-200034783
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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 21, pp. 3909–3914, 2004
A Fast and Efficient Deprotection of
Aldehydes from Acylals Using a
Wells-Dawson Heteropolyacid
.
Catalyst (H6P2W18O62 24H2O)
3
G. P. Romanelli,1,2 J. C. Autino,1, G. Baronetti, and
*
H. J. Thomas2
1
´
Laboratorio de Estudio de Compuestos Organicos (LADECOR),
´
Departamento de Quımica, Facultad de Ciencias Exactas, Universidad
Nacional de La Plata, La Plata, Argentina
´
Centro de Investigacion y Desarrollo en Ciencias Aplicadas “Dr. Jorge J.
2
´
Ronco” (CINDECA), Departamento de Quımica, Facultad de Ciencias
Exactas, Universidad Nacional de La Plata-CONICET,
La Plata, Argentina
3
´ ´
Departamento de Ingenierıa Quımica, Pabellon de Industrias, Facultad de
´
´
Ingenierıa, Universidad de Buenos Aires,
Buenos Aires, Argentina
*
´
Correspondence: J. C. Autino, Laboratorio de Estudio de Compuestos Organicos
´
(LADECOR), Departamento de Quımica, Facultad de Ciencias Exactas, Universidad
Nacional de La Plata, Calles 47 y 115, B1900AJL, La Plata, Argentina; Fax: þ54221
4220288; E-mail: jautino@quimica.unlp.edu.ar.
3909
DOI: 10.1081/SCC-200034783
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

3910
Romanelli et al.
ABSTRACT
A rapid and efficient method for the deprotection of aldehyde 1,1-
diacetates is described. The reaction was carried out using a Wells-
Dawson type catalyst supported on silica. The catalyst, used in 1%
molar quantity, is easily recoverable and reusable and maintains the
activity after its use in four consecutive reaction batches. The yield
of the deprotection was 92–100% (15 examples including nitro-
benzaldehyde 1,1-diacetates). Reaction conditions involve short times
and the use of toluene as the solvent; isolation is simple and the products
are nearly pure.
Key Words: Acylal; Aldehyde; 1,1-Diacetate; Heteropolyacid; Protect-
ing group; Wells-Dawson catalyst.
INTRODUCTION
Aldehydes are conveniently and selectively protected as 1,1-diacetates
(acylals) as an alternative to the formation of acetals;[1,2] moreover, some
acylals are compounds of technological interest, and have been applied
e.g., as synthetic precursors of functionalized butadienes for Diels Alder
reactions.[3] Formation of acylals is involved in some preparation methods
for substituted aldehydes from toluenes.[4]
The main reported procedures for performing the cleavage of 1,1-
diacetates to the corresponding aldehydes were accounted recently.[5] These
procedures involve catalysis by mineral acids, alkaline bases, boron triiodide-
diethylaniline complex, CAN coated on silica gel, neutral alumina under
microwave irradiation, Montmorillonite K-10 and expansive graphite. In
addition, bismuth (III) chloride,[6] type Y zeolite (HSZ-360),[7] and scandium
[8]
[9]
triflate
reported.
have been used. More recently, a method using of CBr4
was
The problems associated with both the handling and disposal of con-
ventional inorganic acids have raised the interest in the development of
alternative clean processes and technologies involving the use of solid acid
.
catalysts. Wells-Dawson (WD) type heteropolyacid (H6P2W18O62 24H2O)
showed to be useful and versatile for the catalysis of a number of reactions.
Among these are the preparation of MTBE from methanol and
isobutylene,[10] epoxidation of alkenes and alkenols,[11] deprotection of
MOM-ethers of phenols,[12] protection of alcohols and phenols as THP-
acetals and their deprotection,[13] protection of aldehydes as acylals,[2] and a
Michael reaction involving alkylation of cyclohexanone with alcohols.[14]

Deprotection of Aldehydes from Acylals Using Wells-Dawson Catalysis
3911
Wells-Dawson acid was prepared as described elsewhere[10] from an
.
aqueous solution of a/b K6P2W18O62 10H2O salt, which was treated with
ether and concentrated (37%) HCl solution. Silica-supported WD acid con-
taining 20% by weight was attained by wet impregnation of Grace-Davidson
silica (Grade 59, specific area ¼ 250 m2/g) with an aqueous solution of the
WD acid. After the impregnation, samples were dried at room temperature
in a vacuum dessicator for 8 h. WD acid can be utilized both in bulk or
supported forms, and both homogeneous and heterogeneous catalysis are
possible. Structure of WD heteropolyacid was already studied.[10]
DISCUSSION
In line with our previous article[2] a simple and rapid procedure to
deprotect aldehydes from 1,1-diacetates is reported here, as a result of a
research project for developing environmentally friendly organic reactions.
We use WD acid as the deprotection catalyst, performing the cleavage
(Sch. 1) in solvent toluene and using 1,1-diacetates 1a–1o as the substrates;
their structure and the results are displayed in Table 1. Phenylmethanediol
diacetate (1a) was selected for optimizing the reaction conditions; effects of
the temperature, time, and aggregation state of the catalyst were examined.
Wells-Dawson acid was tested as bulk and solid-supported samples; in the
latter case silica gel was used as the support.
When aldehyde 1,1-diacetates (1) are heated at 508C in the presence of
1% (mol) of WD acid in toluene, the corresponding aldehydes (2) are
obtained, requiring 45–90 min to attain very good to excellent yields.
Substrates 1a–1f and 1i–1o showed this behavior in such mild conditions.
Nitrophenylmethanediol diacetates (1g, 1h) yielded 85% and 75% aldehyde,
respectively after 6 h. But if the reaction is carried out at 1008C and while
other reaction conditions are kept unchanged, most of the 1,1-diacetates are
deprotected with excellent yields in 5 min. For example, arylmethanediol
diacetates 1a, 1g, 1j, 1k, and 1l gave aldehydes quantitatively, see Table 1;
other examples, even the chloro-substituted 1d and 1e are deprotected with
very good to excellent yields, showing that most of the chosen substituents
Scheme 1. Deprotection of aldehydes from aldehyde 1,1-diacetates.

3912
Romanelli et al.
Table 1. Catalytic conversiona of acylals in aldehydes 2a–ob using WD acid.
Entry
Acylals 1a–o
R
Time (min)
Yield (%)
1
2
a
b
c
d
e
f
C6H5
5
5
100
97
95
95c
95
94
98
97
93
99
100
99
96
93
92
4-CH3C6H4
4-CH3SC6H4
4-ClC6H4
2-ClC6H4
3-C6H5OC6H4
4-NO2C6H4
2-NO2C6H4
2-Cl-6-FC6H3
1-C10H7
3
5
4
5
5
5
6
5
7
g
h
i
10
10
5
8
9
10
11
12
13
14
15
j
5
k
l
2-C10H7
5
C6H5-CH55CH
2-Furyl
C7H15
5
m
n
o
5
5
C10H21
5
aReactions were carried out in toluene, at 1008C.
bAll the yields were calculated from isolated products, being their purity better than
97% by GLC.
cThe used catalyst was recovered and reused three times yielding 96%, 94%, and 94%,
respectively.
at the phenyl ring have no considerable effect on the reaction. Likewise,
nitrophenyl ones deprotect almost quantitatively but require double the time.
All the deprotected aldehydes were identified by comparison (TLC, GLC,
and physical constants) with authentic samples. All the yields were calculated
from isolated products, and GC was used to establish their purities; being
better than 97% in all of the examples.
GENERAL PROCEDURE FOR THE DEPROTECTION OF
ALDEHYDES FROM 1,1-DIACETATES
A mixture of a 1,1-diacetate (1, 0.5 mmol), toluene (1 mL) and Wells-
Dawson catalyst (solid supported, 20% by weight; 1% mmol, ca. 20 mg)
was stirred by the indicated period of time and temperature, see Table 1.
The catalyst was then removed by filtration and washed twice with toluene
(0.5 mL each). The organic solution was washed twice with water (3 mL
each) and then it was dried over anhydrous Na2SO4. The crude products are
better than 97%, as revealed by GLC. Evaporation of the solvent under

Deprotection of Aldehydes from Acylals Using Wells-Dawson Catalysis
3913
reduced pressure and flash column chromatography of the residue on silica
gel gave the practically pure aldehyde 2.
CONCLUSIONS
The deprotection of acylals using Wells-Dawson catalyst is a clean,
general, and inexpensive reaction; their workup is very simple; and the
yields are very good to excellent. The use of these solid catalysts allows
replacement of the usual soluble inorganic acids, contributing in this way to
the reduction of wastes.
ACKNOWLEDGMENTS
The authors thank to CONICET (Argentina) and Universidad Nacional de
La Plata for financial support. HJT, GPR, and GB are members of CONICET.
REFERENCES
1. Greene, T.W.; Wuts, P.G.M. Protection for the carbonyl group. In
Protective Groups in Organic Synthesis, 2nd Ed.; John Wiley:
New York, 1991; 184.
2. Romanelli, G.P.; Thomas, H.J.; Baronetti, G.; Autino, J.C. Solvent-free
catalytic preparation of 1,1-diacetates from aldehydes using a Wells-
.
Dawson acid (H6P2W18O62 24H2O). Tetrahedron Lett. 2003, 44,
1301–1303.
3. Banks, R.E.; Miller, J.A.; Nunn, J.M.; Stanley, P.; Weakley, T.J.R.;
Ullah, Z. Diels-Alder route to potential trichothecene precursors.
J. Chem. Soc. Perkin Trans. 1 1981, 1096–1102.
4. (a) Lieberman, S.V.; Connor, R. p-Nitrobenzaldehyde. Org. Synth. 1951,
2, 441–443; (b) Tsang, S.M.; Wood, E.H.; Johnson, J.R. o-Nitrobenzalde-
hyde. Org. Synth. 1955, 3, 641–643.
5. Jin, T-.S.; Ma, Y-.R.; Zhang, Z-.H.; Li, T.-S. An efficient and facile
procedure for the deprotection of 1,1-diacetates catalysed by expansive
graphite. Synth. Commun. 1997, 27, 3379–3383 (and references cited
therein).
6. Mohammadpoor-Baltork, I.; Aliyan, H. Bismuth (III) chloride; an
efficient and selective catalyst for deprotection of 1,1-diacetates. Synth.
Commun. 1999, 29, 2741–2746.

3914
Romanelli et al.
7. Ballini, R.; Bordoni, M.; Bossica, G.; Maggi, R.; Sartori, G. Solvent free
synthesis and deprotection of 1,1-diacetates over a commercially avail-
able zeolite Y as a reusable catalyst. Tetrahedron Lett. 1998, 39,
7587–7590.
8. Aggarwal, V.K.; Fonquerna, S.; Vennall, G.P. Sc(OTf)3, an efficient
catalyst for formation and deprotection of geminal diacetates (acylals);
chemoselective protection of aldehydes in presence of ketones. Synlett
1998, 849–850.
9. Ramalingam, T.; Srinivas, R.; Subba Reddy, B.V.; Yadav, J.S. A mild and
efficient cleavage of gem-diacetates to aldehydes by CBr4. Synth.
Commun. 2001, 31, 1091–1095.
10. Baronetti, G.; Briand, L.; Sedran, U.; Thomas, H. Heteropolyacid-based
catalysis. Dawson acid for MTBE synthesis in gas phase. Appl. Catal.
A 1998, 172, 265–272.
11. Ben-Daniel, R.; Khenkin, A.M.; Neumann, R. The nickel-substituted
quasi-Wells-Dawson-type polyfluoroxometalate, [NiII(H2O)H2F6NaW17
O55]92, as a uniquely active nickel-based catalyst for the activation of
hydrogen peroxide and the epoxidation of alkenes and alkenols. Chem.
Europ. J. 2000, 6, 3722–3728.
12. Romanelli, G.P.; Autino, J.C.; Baronetti, G.; Thomas, H. Efficient
deprotection of phenol methoxymethyl ethers using a solid acid catalyst
with Wells-Dawson structure. Molecules 2001, 6, 1006–1011.
13. Romanelli, G.P.; Baronetti, G.; Thomas, H.; Autino, J.C. Efficient method
for tetrahydropyranylation/depyranylation of phenols and alcohols using
a solid acid catalyst with Wells-Dawson structure. Tetrahedron Lett.
2002, 43, 7589–7591.
14. Kengaku, T.; Matsumoto, Y.; Na, K.; Misono, M. Michael addition in
the pseudoliquid phase of heteropoly compounds. J. Mol. Catal. 1998,
134, 237–242.
Received in the USA May 13, 2004