Preparation and deprotection of 1,1-diacetates (acylals) using zirconium sulfophenyl phosphonate as catalyst

Article abstract of DOI:10.1016/S0040-4039(02)00369-6

Layered zirconium sulfophenyl phosphonate was found to be an efficient heterogeneous catalyst for the preparation and deprotection of 1,1-diacetates.

Full text of DOI:10.1016/S0040-4039(02)00369-6

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 2709–2711
Preparation and deprotection of 1,1-diacetates (acylals) using
zirconium sulfophenyl phosphonate as catalyst
a,
a
a
a
Massimo Curini, * Francesco Epifano, Maria Carla Marcotullio, Ornelio Rosati and
b
Morena Nocchetti
a
Dipartimento di Chimica e Tecnologia del Farmaco, Sezione di Chimica Organica, Facolt a` di Farmacia, Universit a` degli Studi,
Via del Liceo, I-06123 Perugia, Italy
b
Dipartimento di Chimica, Universit a` degli Studi, Via del Liceo, I-06123 Perugia, Italy
Received 7 February 2002; revised 13 February 2002; accepted 22 February 2002
Abstract—Layered zirconium sulfophenyl phosphonate was found to be an efficient heterogeneous catalyst for the preparation
and deprotection of 1,1-diacetates. © 2002 Elsevier Science Ltd. All rights reserved.
1
Acylals are synthetically useful protecting groups for
carbonyl compounds due to their stability and also
important building blocks for the synthesis of dienes in
ene sulfonic resin, does not show marked swelling
phenomena in the presence of apolar or slightly polar
solvents and possesses a good thermal resistance.
2
Diels–Alder reaction.
Herein we report a simple and efficient method for the
preparation and deprotection of 1,1-diacetates from
aldehydes using zirconium sulfophenyl phosphonate as
catalyst (Scheme 1).
Usually the preparations of acylals were carried out
3
4
using several catalysts such as protic or Lewis acid,
5
6
iodine, NBS. The reported methods entail the prob-
lems of yield, long reaction time, corrosivity and
difficult work-up. More recently the use of bismuth
7
8
triflate and lithium tetrafluoroborate as catalysts has
been reported. Several reports are available using het-
9
erogeneous catalyst such as zeolites, sulfated zirco-
nia, montmorillonite clay, expansive graphite and
zeolite HSZ-360. However, none of the above men-
tioned catalysts is claimed to give protection as well as
deprotection except expansive graphite and HSZ-
1
0
11
12
1
3
Scheme 1.
12
1
3
As shown in Table 1 different aromatic aldehydes are
converted to the corresponding 1,1-diacetates in solvent
free conditions using acetic anhydride as acylating
agent in the presence of zirconium sulfophenyl phos-
phonate at room temperature in high yield and short
reaction time (entries 1–8). Aliphatic as well as a,b-
unsaturated aldehydes react in the same conditions
leading acylals in good yield (entries 9–12).
360.
We have recently reported that layered zirconium sul-
fophenyl phosphonate bearing strongly acidic C H –
6
4
SO H groups anchored to inorganic layers is an
3
excellent heterogeneous catalyst for acid-catalyzed reac-
1
4
tions. The acid strength (Ho) of the catalyst should lie
between pK values of −5.6 and −8.2 and it is similar to
a
that of hydrogen montmorillonite but higher than that
of Amberlyst 15. The strongly acidic catalyst compares
favorably with the more common styrene–divinylbenz-
It is worth noting that ketones were acetilated under
these conditions in very poor yield (entry 13), or did
not react at all (entry 14), hence the above method
represents a selective preparation of acylals of alde-
hydes in the presence of ketones.
Keywords: 1,1-diacetates (acylals); aldehydes; protection; deprotec-
tion; zirconium sulfophenyl phosphonate.
*
Corresponding author. Tel.: +39-075-5855106; fax: +39-075-
855116; e-mail: curmax@unipg.it
In a separate experiment an equimolar mixture of
cyclohexanecarbaldehyde and cyclohexanone were kept
5
0
040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)00369-6

2
710
M. Curini et al. / Tetrahedron Letters 43 (2002) 2709–2711
Table 1. Zirconium sulfophenyl phosphonate-catalyzed acylal formation and deprotection
under usual acylating conditions affording after 12 h
the corresponding acylals with 73% of total yield and a
procedure only aromatic and a,b-unsaturated acylals
have been transformed into the corresponding alde-
16:1 ratio; no other products were observed.
hydes in high yields (entries 1–8).
We next investigated the use of catalyst in deprotection
of 1,1-diacetates to the corresponding aldehydes by
treatment of 1,1-diacetates with zirconium sulfophenyl
phosphonate in commercial dioxane at 50°C; by this
When the reaction was carried out using aliphatic
acylals, we obtained poor yields (32% for entry 11) or
we recovered unreacted starting material (entries 10, 12
and 13).

M. Curini et al. / Tetrahedron Letters 43 (2002) 2709–2711
2711
The important features of this method are: mild reac-
tion condition, simple work up and recyclable nature of
U. Tetrahedron Lett. 1998, 39, 8159; (d) Curini, M.;
Epifano, F.; Marcotullio, M. C.; Rosati, O.; Costantino,
U. Synth. Commun. 1999, 541–546; (e) Curini, M.; Epi-
fano, F.; Marcotullio, M. C.; Rosati, O. Synth. Commun.
1
5
the catalyst, the preparation of which does not require
1
4a
particular skill.
2000, 1319; (f) Curini, M.; Epifano, F.; Marcotullio, M.
In conclusion we report an efficient and selective
method for the preparation of 1,1-diacetates from alde-
hydes in solvent free conditions, and a selective regener-
ation of aromatic aldehydes from the corresponding
acylals using zirconium sulfophenyl phosphonate as
catalyst.
C.; Rosati, O. Synlett 2001, 1182; (g) Curini, M.; Epi-
fano, F.; Marcotullio, M. C.; Rosati, O. Eur. J. Org.
Chem. 2001, 21, 4149.
15. The catalyst, washed with dichloromethane and dried at
160°C, can be reused for several experiments. The reac-
tion in entry 3 has been repeated three times with the
following yields: 90, 87, 88%.
6. Analytical data for 4-formylphenyl acetate. H NMR
1
1
Acknowledgements
(CDCl
and 1.2 Hz, 1H), 7.54 (t, J=8.0 Hz, 1H), 7.60 (m, 1H),
.74 (br ddd, J=7.5, 1.2 and 1.2 Hz, 1H), 9.82 (s, 1H);
3
, 200 MHz): l 2.38 (s, 3H), 7.35 (ddd J=8.0, 2.6
7
+
This work was supported by MURST ‘Progetto Chim-
ica dei Composti Organici di Interesse Biologico’, and
the CNR (Rome) is gratefully acknowledged. We thank
Professor U. Costantino for helpful discussions.
GC–MS (m/z) 93, 122, 164 (M ). Anal. calcd for
: C, 65.85; H, 4.91. Found: C, 65.82; H, 4.93.
C H O
9 8 3
17. Analytical data for selected compounds:
1
(2E)-3-Phenylprop-2-ene-1,1-diacetate: H NMR (CDCl
,
3
200 MHz): l 2.15 (s, 6H), 6.20 (dd J=15.1 and 6.8 Hz,
1
H), 6.75 (d, J=15.1 Hz, 1H), 7.25–7.65 (m, 6H); GC–
+
References
MS (m/z) 77, 104, 131, 174, 234 (M ). Anal. calcd for
C H O : C, 66.66; H, 6.02. Found: C, 66.63; H, 6.05.
13
14
4
1
1
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12 14 5
18. Typical procedure for the preparation of 1,1-diacetates: To
a stirred suspension of aldehydes (1 mmol) and zirconium
sulfophenyl phosphonate (20 mg) acetic anhydride (3
mmol) was added at room temperature with progress of
reaction monitored by GC–MS. Stirring was continued
for the appropriate time (see Table 1). The catalyst was
then filtered and washed with dichloromethane, the
organic layer was washed twice with a 5% solution of
sodium bicarbonate, dried over anhydrous sodium sulfate
and evaporated under reduced pressure. The residue was
purified by flash chromatography (eluent hexane/ethyl
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2
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4
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1
1,1-diacetates. All compounds were characterized by H
17
NMR and GC–MS.
19. Typical procedure for the deprotection of 1,1-diacetates:
To a stirred solution of 1,1-diacetate (1 mmol) in com-
mercial dioxane (1 ml) was added zirconium sulfophenyl
phosphonate (20 mg) at 50°C. Stirring was continued for
the appropriate time (see Table 1) with progress of reac-
tion monitored by GC–MS. The catalyst was then filtered
and washed with dichloromethane. The organic layer was
washed twice with 5% solution of sodium bicarbonate,
dried over sodium sulfate and evaporated under reduced
pressure. The residue was purified by flash chromatogra-
phy (eluent hexane/EtOAc 15:1) to give the correspond-
ing aldehydes.
1
1
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