Rice husk supported FeCl3 nanoparticles as an efficient and reusable catalyst for the chemoselective 1,1-diacetate protection and deprotection of aldehydes

Article abstract of DOI:10.1016/j.molcata.2012.05.010

1,1-Diacetates were produced from a variety of aromatic aldehydes using rice husk supported FeCl₃ nanoparticles as a catalyst. The procedure generally resulted in good yields (98%) of aromatic aldehydes including those carrying electron donating- or withdrawing-substituents. Deprotection of the resulting 1,1-diacetates was also achieved using the same catalyst in ethanol. This new method consistently has the advantages of excellent yields and relatively short reaction times. Further, the catalyst can be reused and recovered for several times.

Full text of DOI:10.1016/j.molcata.2012.05.010

Journal of Molecular Catalysis A: Chemical 363–364 (2012) 10–17
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Rice husk supported FeCl nanoparticles as an efficient and reusable catalyst for
3
the chemoselective 1,1-diacetate protection and deprotection of aldehydes
∗
Farhad Shirini , Somayeh Akbari-Dadamahaleh, Ali Mohammad-Khah
Department of Chemistry, Faculty of Sciences, University of Guilan, Rasht, zip code: 41335, Post Box: 1914, Islamic Republic of Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
1,1-Diacetates were produced from a variety of aromatic aldehydes using rice husk supported FeCl3
nanoparticles as a catalyst. The procedure generally resulted in good yields (98%) of aromatic aldehydes
including those carrying electron donating- or withdrawing-substituents. Deprotection of the resulting
Received 4 February 2012
Received in revised form 8 May 2012
Accepted 9 May 2012
1
,1-diacetates was also achieved using the same catalyst in ethanol. This new method consistently has
Available online 18 May 2012
the advantages of excellent yields and relatively short reaction times. Further, the catalyst can be reused
and recovered for several times.
Keywords:
Rice husk supported FeCl3 nanoparticles
©
2012 Elsevier B.V. All rights reserved.
(
1
FeCl3-RiH)
,1-Diacetates
Aldehydes
Heterogeneous catalyst
Deprotection
1
. Introduction
reaction time, involvement of expensive reagents, use of additional
reagents, requirement of special effort for catalyst preparation,
need to use special apparatus, moderate yields, and side reactions.
The most serious drawback is that these methods have no global
utility and most of the products are liquid, which may contain
impurities and are difficult to be purified compared to the powder
and crystal.
Protection of aldehydes is a frequently desired exercise in
organic synthesis as it is often necessary to carry out a reaction
on a multifunctional substrate without affecting ␣-carbonyl group
[
1]. Aldehydes are often protected by acetalization through reac-
tion between aldehydes and alcohols [2] or trimethyl orthoformate
3] and by the reaction of aldehydic compound with acetic anhy-
[
Furthermore, many of these methods involve cumbersome
product isolation procedure and there are only a few reagents,
such as: CAN [8], ZrCl [26], InBr [27], and poly(4-vinylpyridinium)
dride in the presence of a Brönsted acid or Lewis acid, which act
as a catalyst. Among these methods, protection of aldehydes as
their corresponding 1,1-diacetates has attracted the attention of
many organic chemists. This attention can be attributed to their
remarkable stability to neutral and basic conditions [4], and their
applicability as building blocks for asymmetric allylic alkylation
and Diel’s Alder reaction [5,6]. Some of the reagents and catalysts
that have recently been employed for the promotion of this type
of reactions are: LiOTf [7], ceric ammonium nitrate [8], InCl3 [9],
H NSO H [10], LiBF [11], H SO4 [12], PCl3 [13], NBS [14], I2 [15],
4
3
hydrogen sulfate [28], which are applicable to both, the synthesis
of acylals as well as for their conversion to parent carbonyls. There-
fore, there is a scope to find out an alternative method, which might
be mild and catalytically efficient.
The above mentioned subjects encouraged us to prepare the rice
husk supported FeCl3 nanoparticles as a new, efficient and hetero-
geneous reagent. Our investigations clarified that this reagent is
efficiently able to catalyze the chemoselective protection of alde-
hydes as their corresponding 1,1-diacetates and deprotection of the
obtained acylals. All reactions are performed under mild reaction
conditions in short reaction times in good to high yields.
2
3
4
2
TMSCl-NaI [16], FeCl3 [17], and Bi(NO ) ·5H O [18]. Some metal
3
3
2
triflates, such as Cu(OTf)2 [19], and Sc(OTf)3 [20], in environmen-
tally harmful organic solvents (e.g., CH Cl2 [21–24], CH CN [24],
2
3
CH NO2 [25]), have also been utilized as catalysts for the prepara-
3
tion of 1,1-diacetate derivatives from the corresponding aldehydes.
Many of these methods have certain drawbacks, such as long
2. Experimental
2.1. General
∗ Corresponding author. Tel.: +98 131 3233262; fax: +98 131 3233262.
E-mail address: shirini@guilan.ac.ir (F. Shirini).
Chemicals were purchased from Fluka, Merck, Aldrich and
Southern Clay Products Chemical Companies. Yields refer to
1
381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2012.05.010

F. Shirini et al. / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 10–17
11
Fig. 1. The infrared spectra of RiH in comparison of FeCl3-RiH.
isolated products. Products were characterized by their physical
constants, comparison with authentic samples and IR and NMR
spectroscopy. The purity determination of the substrate and reac-
tion monitoring were accomplished by TLC on silica-gel polygram
SILG/UV 254 plates.
2.4. Preparation of the catalyst (FeCl -RiH)
3
The catalyst was prepared by impregnation of rice husk (RiH)
(50 g) with a solution of anhydrous FeCl (0.053 mol, 8.62 g) in ace-
3
tone. The solvent was evaporated under reduced pressure and the
◦
catalyst was heated at 120 C for 8 h to give FeCl -rice husk (58 g).
3
2.2. Instrumentation
The IR spectra were run on a Perkin-Elmer bio-spectrometer and
Bruker Vector 22. The 1H NMR (400 MHz) and C NMR (100 MHz)
were run on a Bruker AVANCEIII-400 spectrometer in CDCl3 using
TMS as an internal reference (ı in ppm). Microanalyses were per-
formed on a Perkin-Elmer 240-B microanalyzer. Melting points
were recorded on a Büchi B-545 apparatus in open capillary tubes.
The characterization of rice husk was obtained using scanning elec-
tron microscopy (SEM-Philips XL30) with field emission gun and
energy dispersive spectroscopy (EDS). Prior to placing into the
microscope, the rice husk particles were coated with gold under
vacuum (SCD 005 sputter coater, Bal-Tec, Swiss) and examined at
an acceleration voltage of 17 kV. X-ray diffractometry (XRD) dia-
grams of the samples were obtained with a diffractometer Model
XRD 6000, PHILIPS Xpert pro. The chemical composition of RHA
was analyzed using X-ray fluorescence (XRF) spectrometer (Model
Magix Pro, Philips).
13
2.3. Preparation of rice husk
Rice sample (named as Hassani) was obtained from Rasht
(
Guilan Provience) in the north of Iran. Rice husk was obtained from
a local mill, washed several times with distilled water to remove
any adhering materials and dried at room temperature for 48 h. The
dried RiH smashed and sieved (80–170 mesh size), washed with
◦
distilled water and dried at 110 C for 4 h.
The main components of the rice husk sample were determined
as follow, using the reported methods in the literature [29,30]: sil-
ica (14.2%), cellulose (27.4%), hemicelluloses (18.3%), lignin (25.8%),
inorganic residue (9.3%), and moisture (5%).
Fig. 2. SEM micrographs of untreated rice husk (mesh 80–170).

1
2
F. Shirini et al. / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 10–17
Fig. 3. SEM micrographs of FeCl3-rice husk (mesh 80–170).
2
.5. Catalyst characterization
.5.1. IR analysis
2.5.2. SEM analysis
Fiber sizes and shapes are one of the most important fac-
2
tors for composite materials. The effective surface area which
may have influence on chemical properties depends on particle
size and shape. Figs. 2 and 3 show the SEM micrographs of the
rice husk and rice husk supported FeCl3 nano-particles, respec-
tively. Fig. 2a shows layering sequences of phyllosilicate [34] and
Fig. 2b shows particle size and shape of the rice husk. There are
Fig. 1 shows the FTIR spectra of the RiH and FeCl -RiH. The
3
spectra are virtually identical. This implied that FTIR is not sen-
sitive to change in the system. In the stretching region, two peaks
at 3400–3480 cm and 2950–2970 cm are observed in both of
spectra. The broad band in the range 3430–3480 cm is due to the
stretching vibration of O H bond. This band is due to the silanol OH
groups and the adsorbed water bound to the silica surface, and the
peak at about 2900 cm is due to the C H stretching from aliphatic
saturated compounds [31]. 1600–1750 cm and 1400–1600 cm
assigned to C O stretching of hemicelluloses and lignin and C
−1
−1
−
1
−1
Table 1
XRF analysis.
−1
−1
,
C
Elements
Percentage in RiH
Percentage in FeCl3-RiH
stretching of aromatic carbon respectively [32]. The strong peaks
L.O.I.
Al2O3
SiO2
P2O5
SO3
CaO
Fe2O3
Cl
82.33
0.07
16.54
0.28
0.18
0.32
0
76.17
0.04
7.73
0.04
0.08
0.08
7.60
8.27
−1
between 1025 and 1100 cm are due to the structural siloxane
bond, Si Si. These peaks are observed in both RiH and metal
incorporated RiH. The band at 800–805 and 460–475 cm in all
spectra are due to the deformation of Si O bond. In the FeCl -RiH
O
−
1
3
−1
spectra the shoulder at 910 cm is due to the Fe
33].
O Si vibration
0.29
[

F. Shirini et al. / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 10–17
13
Table 2
Influence of the size of RiH (50 g) and the amounts of FeCl3 and FeCl3-RiH on the time and conversion of benzaldehyde to its corresponding 1,1-diacetate and deprotection
of the obtained 1,1-diacetate.
Entry
FeCl3 (g)
RiH (mesh)
Protection
Catalyst (g)
Deprotection
Catalyst (g)
Time (min)
Conversion (%)
80
Time (min)
Conversion (%)
85
1
2
3
4
5
6
7
8
9
3.93
5.24
7.56
8.62
9.87
8.62
8.62
8.62
8.62
8.62
–
80–170
80–170
80–170
80–170
80–170
50–80
170–200
80–170
80–170
80–170
–
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.01
0.015
0.03
–
60
40
30
20
20
45
20
30
30
20
90
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.02
0.06
0.1
65
95
100
100
100
100
100
80
95
100
0
40
30
90
95
20
20
30
20–25
60
100
100
100
100
50
25
80
1
1
0
1
20
90
100
0
–
2.7. XRF analysis
X-ray fluorescence (XRF) is the emission of characteristic “sec-
ondary” (or fluorescent) X-rays from a material that has been
excited by bombarding with high energy X-rays or gamma rays. XRF
technology provides one of the simplest, most accurate and most
economic analytical methods for the determination of the chemical
composition of many types of materials.
The loss on ignition (L.O.I.) of RiH and FeCl -RiH is determined
3
◦
by heating 3 g of each sample at 1000 C for 1 h in air to remove
the moisture and the coexisting unburned carbon. Table 1 shows
the percentage of the elements of RiH with silica as the major ele-
ment (∼16.54%). Other metallic elements are also present in RiH as
minor elements. The composition of rice husk supported with FeCl3
nanoparticles determined by XRF are listed in Table 1. The results
Fig. 4. XRD patterns of RiH (top) and FeCl3-RiH (down).
clearly show that the Fe content is increased in FeCl -RiH.
3
different types of fiber shape observed. Most of the particles
are round and angular. Particle size (length) distribution is not
same. All these samples show a structure mainly formed by
elongated pores (tubular). The sizes of the pores are about
2.8. General procedure for the acetylation of aldehydes
Aldehyde (1 mmol), acetic anhydride (2.5 mmol), and FeCl -rice
husk (0.02 g) were mixed at room temperature. The reaction was
monitored by TLC. After completion of the reaction ethylacetate
3
3
–10 ␮m. The micrographs reveal clearly the presence of cylindri-
cal structures, with different diameters, after metal ion sorption
Fig. 3a–d); these structures were absent on the rice bran before
(
(15 mL) was added to the reaction mixture and the catalyst was
the sorption process. Covered on the substrate, the FeCl3 of
RiH are nanoparticles with diameters of 100–900 nm (Fig. 3c).
The SEM observations prove that the rice husk supported FeCl3
nano-particles catalyst have been successfully prepared. The
presence of pellets on the rice bran particles and inside the
cylindrical structures can also be observed after metal ion sorp-
tion. The results are in accordance with the earlier report
recovered by filtration, and washed with ethylacetate (5 mL). The
organic layer was washed with a saturated solution of NaHCO3
(
3 × 15 mL) and water (2 × 10 mL). The organic phase was dried over
anhydrous MgSO , filtered and the solvent was evaporated to give
4
the pure desired compounds. The solid crude product that obtained
was purified by recrystallization from cyclohexane, or by column
chromatography on a silica gel column.
[
35].
The spectral (IR, 1H and 13C NMR) data of new compounds are
presented below:
2.6. XRD analysis
The XRD patterns of the samples are shown in Fig. 4. As indicated
by the featureless diffractometers and the appearance of a diffuse
maximum at 2ꢀ = 25.5, which is typical for amorphous silica [36],
it can be concluded that the rice husk and FeCl -rice husk (Fig. 4)
3
are completely amorphous and did not show crystalline structure.
The XRD patterns of FeCl -RiH also show a decrease in the line
3
intensities after the addition of FeCl3 to the rice husk sample.
Ac O (2.5 mmol), FeCl -RiH (0.02 g), Solvent-free, r.t.
OAc
OAc
RCHO
2
3
R
(
1 mmol)
FeCl -RiH (0.08 g), EtOH, 70 C
3
R= Ar, Alkyl
Fig. 5. Reusability of FeCl3-RiH in the conversion of benzaldehyde to its correspond-
Scheme 1. Protection of aldehydes with acetic anhydride and deprotection of 1,1-
diacetates in the presence of FeCl3-RiH.
ing 1,1-diacetates and deprotection of the obtained 1,1-diacetate (Table 2, entry
1).

1
4
F. Shirini et al. / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 10–17
Table 3
Acylation of aldehydes and deprotection of acylals in the presence of FeCl3-RiH.
a
Entry
Aldehyde
1,1-Diacetate
Protection
Time (min)
Deprotection
Time (min)
Yield (%)
Yield (%)
OAc
OAc
CHO
1
2
3
4
5
6
20
20
25
15
40
10
94
20
96
OAc
OAc
CHO
Cl
F
Cl
F
92
91
96
94
96
18
15
20
6
93
92
93
91
96
OAc
OAc
CHO
OAc
OAc
CHO
CHO
Br
NC
Br
NC
OAc
OAc
OAc
OAc
CHO
H CO
3
H CO
3
5
OAc
OAc
CHO
CHO
H C
H C
3
3
7
8
10
35
94
93
8
93
91
OAc
OAc
O N
2
O N
2
12
OAc
OAc
CHO
AcO
Cl
OHC
Cl
OAc
OAc
9
25
30
92
92
15
5
91
93
CHO
OAc
1
1
1
0
1
2
OAc
OAc
CH3
OAc
CHO
CH3
15
12
94
92
15
10
96
95
CHO
OAc
OCH3
CHO
OCH3
OAc
OAc
Cl
Cl
1
3
15
93
3
94

F. Shirini et al. / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 10–17
15
Table 3 (Continued)
Entry Aldehyde
1,1-Diacetate
Protection
Time (min)
Deprotection
Time (min)
Yield (%)
Yield (%)
OAc
OAc
CHO
CHO
NO2
NO2
1
4
35
94
15
93
OAc
OAc
CHO
Cl
AcO OAc
Cl
1
5
6
40
25
93
92
35
25
90
92
OAc
CHO
OAc
Cl
Cl
1
OAc
CHO
OAc
H CO
H CO
3
3
OCH3
OCH3
1
1
7
8
10
20
95
96
3
92
95
OAc
OAc
CHO
10
OAc
OAc
CHO
1
9
0
30
25
91
91
5
92
90
OAc
OAc
OAc
OAc
CHO
CHO
2
15
2
2
1
2
25
25
94
93
10
25
90
94
OAc
OAc
O
O
CHO
O
AcO
OAc
2
3
120
30
0
–
–
100b
–
–
2
4
OAc
CHO
O
OAc
+
+
AcO
OAc
0b
a
Yields refer to pure isolated products and the products were characterized by m.p., IR and 1H NMR.
Conversion.
b

1
6
F. Shirini et al. / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 10–17
FeCl -RiH
O
O
3
O
O
O
FeCl -RiH +
3
R
H
R
H
Intermolecular
Intramolecular
O
O
O
O
O
OAc
OAc
H
O
H
R
O
O
O
O
FeCl -RiH
FeCl -RiH
3
3
R
O
R
FeCl -RiH
FeCl -RiH
3
3
Scheme 2. Proposed mechanisms.
◦
A: Table 3, entry 9: white solid, m.p. 164–166 C; IR (KBr): 3020,
was washed with a saturated solution of NaHCO3 and dried over
2
9
2
910, 1758, 1430, 1378, 1338, 1200, 1118, 1060, 1008, 960, 940,
MgSO . The solvent was evaporated under reduced pressure. The
resultant product was passed through a short column of silica gel
(n-hexan–EtOAc, 9:1) to afford pure aldehyde.
4
−1 1
10, 852, 818, 604, 580, and 540 cm . H NMR (300 MHz, CDCl ):
3
.37 (s, 6H, 2× COCH ), 7.29 (d, 1H, J = 5.7 Hz, ArH), 7.41 (d, 1H,
3
13
J = 5.1 Hz, ArH), 8.26 (s, 1H, CH(OAc) ) ppm; C NMR (75 MHz,
2
DMSO): 167.00, 141.19, 129.82, 104.33, and 21.55 ppm.
B: Table 3, entry 10: white solid, m.p. 65–67 C; IR (KBr): 3650,
3. Results and discussion
◦
3
1
500, 3010, 2910, 1760, 1610, 1590, 1490, 1430, 1370, 1245, 1200,
In recent years, investigation on the application of silica-based
−
1
160, 1060, 1010, 970, 940, 917, 790, 760, 700, 670, and 600 cm
.
reagents in organic reactions became an important part of our
ongoing research program [37–41]. In continuation of these stud-
ies, we were interested to investigate the applicability of rice husk
RiH), as a source of amorphous silica [42], in these type of reactions.
Herein, and for the first time we report the preparation of rice husk
1
H NMR (300 MHz, DMSO-d6): ı 2.13 (s, 6H, 2× COCH ), 3.38 (s,
3
3
H, CH ), 7.02 (d, 1H, J = 7.9 Hz, ArH), 7.50 (d, 1H, J = 7.9 Hz, ArH),
3
7
.60–7.66 (m, 2H, J = 8.3, J = 7.7 Hz, ArH), 8.04 (s, 1H, CH(OAc) )
2
(
13
ppm; C NMR (75 MHz, DMSO-d6): ı 167.55, 147.74, 135.42,
1
33.82, 127.94, 125.12, 123.53, 87.83, 21.93, and 21.00 ppm.
supported FeCl3 nano-particles (FeCl -RiH) and its application in
◦
3
C: Table 3, entry 15: white solid, m.p. 96–98 C; IR (KBr): 3002,
the efficient and chemoselective conversion of aldehydes to their
corresponding 1,1-diacetates with acetic anhydride and deprotec-
tion of the obtained 1,1-diacetates. All reactions are performed
under mild reaction conditions in good to high yields.
First of all and for obtaining the optimum reaction conditions,
we studied the influence of the following factors on the protec-
tion of benzaldeyde with acetic anhydride: (i) the amounts of FeCl3
and the size of RiH sample used for the preparation of the catalyst;
2
1
920, 1752, 1430, 1362, 1340, 1240, 1200, 1158, 1106, 1060,
000, 942, 910, 808, 710, 680, 650, 600, 530, and 510 cm . 1H
−
1
NMR (300 MHz, DMSO-d6): 2.10 (s, 12H, 4× COCH ), 7.52 (d, 1H,
3
J = 7.8 Hz, ArH), 8.00 (d, 1H, J = 7.9 Hz, ArH), 8.17 (s, 1H, CH(OAc) ),
2
8
.43 (dd, 2H, J = 7.6, J = 8.2 Hz, ArH) ppm; 13C NMR (75 MHz,
DMSO-d6): 167.00, 141.19, 129.62, 128.82, 126.32, 102.33, and
2.55 ppm.
2
(ii) solvent, and (iii) temperature. The results showed that the best
results can be obtained under conditions showed in Scheme 1 using
0.02 g of the catalyst prepared from the addition of 8.62 g FeCl3 on
RiH (50 g, mesh 80–170) (Table 2, entry 4). To illustrate the effi-
ciency of the catalyst in these reactions, acylation of benzaldehyde
was also carried out in the absence of the catalyst (Table 4, entries
11). The reaction was not completed after a long reaction time. This
result indicates that the catalyst is necessary to produce the acylal
product.
2
.9. General procedure for deprotection of 1,1-diacetates
A solution of the substrate (1 mmol) in EtOH (3 mL) was stirred
as FeCl -rice husk (0.08 g) was added. The mixture was stirred and
heated at 70 C. The progress of the reaction was monitored by TLC.
After completion of the reaction, the mixture was filtered to sepa-
rate the solid catalyst. The combined filtrates were concentrated on
a rotary evaporator to remove EtOH. Water (5 mL) was added and
3
◦
Following the above reaction condition, a variety of aromatic
aldehydes are converted to the corresponding 1,1-diacetates under
solvent free conditions using acetic anhydride in the presence of
the product was extracted with Et O (3–5 mL). The organic layer
2
FeCl -RiH at room temperature in excellent yields and short reac-
tion times.
3
Table 4
Comparison of the effect of the catalysts on the acylal protection of 4-
methylbenzaldehyde.
As shown in Table 3, benzylic aldehydes, including different
substituents such as F, Cl, Br, CN, NO , CH3 and OCH3 are con-
2
Entry
Catalyst
Time (min)
Yield (%)
Ref.
verted to their corresponding acylals in good to high yields (Table 3,
entries 1–18). This method is also very useful for the protection of
aliphatic aldehydes (Table 3, entries 19 and 20). Furthermore, ␣,␤-
unsaturated aldehydes, such as cinnamaldehyde (Table 3, entry 21)
and acid sensitive aldehydes, such as furfural (Table 3, entry 22)
reacted well without any decomposition or polymerization under
the selected reaction conditions.
1
2
3
4
5
6
7
NBS
540
210
120
144
35
93
87
90
90
93
0
[43]
[14]
[44]
[44]
[45]
This work
This work
Bi(OTf)3
TBBDA
PBBS
FeCl3
RiH
90
20
FeCl3-RiH
94

F. Shirini et al. / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 10–17
17
Under the same reaction conditions acylation of ketones was
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after 2 h (Table 3, entry 23). Therefore, the method can be useful
for the chemoselective acylation of aldehydes in the presence of
ketones.
[
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◦
with ethylacetate, and then dried at 100 C prior to used and tested
[
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It was seen that the catalyst displayed very good reusability (Fig. 5).
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3
Scheme 2. On the basis of this mechanism, FeCl -RiH catalyzes
the reaction by the electrophilic activation of the aldehyde to
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3
[
[
[
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[
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1
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The advantages of FeCl -RiH over reported catalysts for the
3
acylation of p-methylbenzaldehyde are shown in Table 4. It is
noteworthy that some of the previously reported methods require
longer reaction times.
Having established the preferred reaction conditions, the depro-
tection of several representative acylals was also performed to
demonstrate the versatility and uniqueness of the present reac-
tion conditions (Table 3). Aromatic acylals were converted to the
parent aldehydes in impressive yield (Scheme 1, Table 3, entries
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1
–18). Aliphatic 1,1-diacetates also converted to their aldehydes in
[
[
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3
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4
. Conclusion
2
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from various aldehydes using FeCl -RiH as a new catalyst under
3
solvent free conditions. This catalyst is also a suitable reagent for
the regeneration of aldehydes from the related acylals in EtOH as a
solvent.
This method offers several advantages, compared to those
reported in literature, i.e., (1) mild, highly efficient catalyst activ-
ity, (2) cost efficiency of the catalyst, (3) wide substrate scope (4)
ease of product isolation/purification, (5) high yields of deprotected
products, and (6) the reusability of the catalyst, making it a use-
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2 (2011)
1
8
Acknowledgement
We are thankful to the University of Guilan Research Council for
the partial support of this work.
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