Tungstosulfonic acid as an efficient solid acid catalyst for acylal synthesis for the protection of the aldehydic carbonyl group

Article abstract of DOI:10.1039/c5nj02697k

Tungstosulfonic acid (TSA) has been found to be an efficient solid acid catalyst for the protection of aldehydic carbonyl groups by geminal diacetate (acylal) formation following the nucleophilic addition of acetic anhydride under neat conditions as well as in a solvent. The TSA catalyst is fully characterized by infrared spectroscopy, wide-angle X-ray scattering analysis, and scanning electron microscopy with energy dispersive X-ray spectroscopy. The deprotection of acylals to corresponding aldehydes has also been investigated under the similar conditions. The catalyst can be reused seven times without a significant loss of activity. In addition, no chromatographic separations are needed to obtain the desired products. This method is a green approach for the chemoselective protection of aldehydes in the presence of ketones.

Full text of DOI:10.1039/c5nj02697k

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Tungstosulfonic acid as an efficient solid acid
catalyst for acylal synthesis for the protection of
the aldehydic carbonyl group†
Cite this:DOI: 10.1039/c5nj02697k
Reddi Mohan Naidu Kalla, Mi Ri Kim, Yu Na Kim and Il Kim*
Tungstosulfonic acid (TSA) has been found to be an efficient solid acid catalyst for the protection of
aldehydic carbonyl groups by geminal diacetate (acylal) formation following the nucleophilic addition of
acetic anhydride under neat conditions as well as in a solvent. The TSA catalyst is fully characterized by
infrared spectroscopy, wide-angle X-ray scattering analysis, and scanning electron microscopy with
energy dispersive X-ray spectroscopy. The deprotection of acylals to corresponding aldehydes has also
been investigated under the similar conditions. The catalyst can be reused seven times without a
significant loss of activity. In addition, no chromatographic separations are needed to obtain the desired
products. This method is a green approach for the chemoselective protection of aldehydes in the
presence of ketones.
Received (in Montpellier, France)
2nd October 2015,
Accepted 10th November 2015
DOI: 10.1039/c5nj02697k
www.rsc.org/njc
acid catalysts and the chemical structures of tungstic acid (TA)
and TSA are shown in Fig. 1.
1. Introduction
Heterogeneous solid acid (HSA) catalysts have a variety of
Selective protection of aldehydic carbonyl groups by conversion
advantages over liquid acid catalysts and have received extensive to their corresponding acylals is an important component of
attention in synthetic organic chemistry as a result of their multistep organic syntheses. A crucial property of the acylals
financial and environmental benefits, which include simple formed in this process is their stability in neutral and basic
product separation, possible recycling, and reduced liberation media.4 Reagents available for the protection of aldehydic
of toxic residues into the atmosphere.1 The ability to deploy HSA carbonyl groups include ethanedithiol,5 alcohols,6 2-mercapto-
catalysts under neat experimental conditions is an important ethanol,7 acetic anhydride,8 and trialkyl orthoformate.9 Among
benefit in industrial chemistry. Sulfonic-acid-supported hetero- all of them acetic anhydride is easy to handle and avoids the
geneous catalysts drive difficult organic transformations faster offensive odour. Typically, the formation of acylals is promoted
and employ mild reaction conditions. These catalysts enable by strong protic acids such as NH2SO3H,10 KHSO4,11 and
feasible and cost-effective synthetic procedures. Because solid H2SO412,13 and Lewis acids such as ZrCl4,14 AlCl3,15 and Bi(OTf )3.16
catalysts can be separated from reaction mixtures by simple From economic and environmental points of view the use of
filtration, they can be reused a number of times, which reduces heterogeneous catalysts such as HClO4ÁSiO2,17 MCM-41-SO3H,18
the risk of discharging poisonous reaction residues into the and zeolite bet supported sulfonic acid (BEA–SO3H)19 has also
environment compared with conventional homogeneous catalysts. been reported. However, Lewis acids are susceptible to moisture,
In recent years there has been considerable research activity in and the other catalysts exhibit disadvantages that may include
the use of sulfonic-acid-supported catalysts in synthetic organic the requirement of a long reaction time, high catalyst loading,
reactions. Sulfonic-acid-supported catalysts have attracted attention high temperature, and microwave or ultrasound stimulation.10
because of their many advantages, which include high thermal Therefore, the development of an economical protocol employing
stability, low toxicity, high efficiency, good selectivity, low expense, an easily accessible low toxicity solid acid catalyst and the ability
reusability, and ease of separation of the catalyst from the reaction
mixture.2,3 Tungstosulfonic acid (TSA) is a class of heterogeneous
BK21 PLUS Centre for Advanced Chemical Technology,
Department of Polymer Science and Engineering, Pusan National University,
Busan 609-735, Republic of Korea. E-mail: ilkim@pusan.ac.kr
† Electronic supplementary information (ESI) available: 1H and 13C NMR Spectras
Fig. 1 The chemical structures of TA and TSA.
for the new compounds. See DOI: 10.1039/c5nj02697k
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to proceed under neat conditions is greatly preferred for the
synthesis of acylals. Synthetic heterocyclic compounds are most
important in the fields of organic and medicinal chemistry
because of their broad range of pharmacological applications.
In various research laboratories and chemical industries
enormous quantities of organic solvents are used and are
wasted all over the world. The development of neat (solvent-
free) conditions can play an increasingly vital role in synthetic
organic chemistry, from not only a practical but also an
ecological point of view.20 The most significant goals of ‘‘green
chemistry’’ include atom economy, prevention of waste, use of
renewable feedstock, use of catalytic reagents, reduction of
expenses, easy workup and fast reaction rates.21 Furthermore,
the reduction of by-products and the reduction of evaluated
toxic gas during the reaction are also an important factor in
green chemistry. The most important goals of neat chemistry
are to reduce the use of toxic organic solvents, toxic reagents,
and laborious work-up procedures associated with the synthesis
of various organic compounds.22–29
To the best of our knowledge in the open literature there
have been no reports on the tungstosulfonic acid (TSA) catalysed
synthesis of acylals. Considering this green chemistry in mind
we report herein the use of TSA as a catalyst for the conversion of
aldehydes to acylals using acetic anhydride as a protecting agent,
which is one of the efficient ways of protecting the aldehyde
group. The TSA catalysed reaction was found to be an environ-
mentally benign, solvent-free, inexpensive, non-volatile and non-
corrosive process. In addition the heterogeneous TSA catalyst
was easy to prepare and recycle.30
Scheme 1 Synthesis of a series of acylals (1–25).
and SiO2ÁSO3H34 under neat conditions. The results are summarized
in Table 1. All catalysts gave acceptable yields except STA. In
addition, we attempted the reaction using tungstic acid as a catalyst,
but no desired product was formed after 24 h. The reaction was also
carried out using ClSO3H as a catalyst; however, the yield was low
and the separation of the catalyst from the reaction mixture was
difficult. Subsequently we thought that the low yields could be
improved by combining TA and ClSO3H to form tungstosulfonic
acid, which could be applied to the synthesis of acylals and would be
easily separated from the reaction mixture. Pleasantly, the reactions
proceeded efficiently in high yields. The synergistic properties of TSA
resulted in good yields compared to those of TA or ClSO3H alone.
To compare the effectiveness of neat versus solvent reaction
conditions for the synthesis of 1 was performed using TSA as a
catalyst in different solvents (Table 2). When the reaction was
conducted in protic solvents such as isopropanol (IPA), acetic
acid (AcOH), methanol (MeOH), ethanol (EtOH), or water (H2O),
the reaction proceeded slowly and provided reduced product
yields (Table 2, entries 2–6). However, when aprotic solvents
such as toluene, 1,4-dioxane, chloroform (CHCl3), or dichloro-
methane (CH2Cl2) were used, the reaction proceeded faster and
resulted in higher product yields (Table 2, entries 7–10).
2. Results and discussion
In this work 25 acylals were synthesized by using the environ-
mentally friendly TSA catalyst under neat conditions. Among
them six compounds, 7, 8, 9, 14, 15 and 21, are new compounds.
The method offers many advantages over other literature procedures
in terms of yield, ease of preparation, and recyclability of the catalyst.
Moreover, we studied the deprotection of acylals under solvent-free
conditions. The deprotection of acylals to their corresponding
aldehydes proceeds in good yields in the presence of 2.5 mol%
of TSA.
To establish the optimum catalyst level of TSA the model
reaction was carried out using 1, 1.5, 2, 2.5, and 3 mol% of neat
Table 1 Effect of various catalysts on the synthesis of compound 1 under
neat conditionsa
Entry Catalyst
Catalyst amount (mol%) Time (h) Yieldb (%)
2.1. Chemistry
1
2
3
4
5
6
7
8
Catalyst free
STA31
SiO2ÁB(OH)233
KHSO4ÁSiO2
SiO2ÁSO3H34
TA
ClSO3H
TSA
TSA
—
7
5
5
5
5
1
1
1.5
2
24
2
0.3
0.5
0.6
24
0.1
0.5
0.1
0.1
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35
75
78
88
nrc
75
84
91
96
99
99
In general the protection of aldehydes is very important one
during multistep synthesis. Furthermore, the protection of
aldehydes by reaction with acetic anhydride is impossible to
proceed without the use of a catalyst. The preparation of acylals
usually requires high catalyst loadings, long reaction times, and
exotic reagents to promote the formation of the desired product.
To avoid these problems we performed acylal formation reaction
in the presence of TSA that is inexpensive, easy to prepare, and
recyclable under mild and neat reaction conditions (Scheme 1).
As a first step we investigated acylal synthesis using several
inexpensive and easily prepared solid-supported acid catalysts
including silicatungstic acid (STA),31 SiO2ÁB(OH)2,32 KHSO4ÁSiO2,33
32
9
10
11
12
TSA
TSA
TSA
2.5
3
0.03
0.03
a
Reaction conditions: p-methyl benzaldehyde = 1 mmol, acetic anhydride =
1 mmol, and TSA = 2.5 mol%. b Isolated yield measured gravimetrically.
c
No reaction.
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Table 2 Effects of various solvents on the synthesis of compound 1a
(after stirring for a few minutes) indicating the completion of the
reaction. Exceptions to this rule are the 4-ethoxy-and 4-isopropyl-
benzaldehyde derivatives (7 and 19), in which case liquids are
obtained as indicated by thin layer chromatography (TLC).
Aliphatic aldehydes (24 and 25) also formed liquids and were
identified by TLC. In the case of p-dimethylamino salicylaldehyde
and p-(N,N-dimethylamino)benzaldehyde TSA was notable to
catalyse the conversion to the corresponding acylals (17 and 18).
No reaction was observed for acetophenone at room temperature
after 24 h as well as at 60 1C after 12 h. No new spot was observed by
TLC, and no corresponding protons were observed in the NMR
spectrum. Encouraged by this result, we conducted a competitive
reaction involving the acylation of p-methyl benzaldehyde in the
presence of acetophenone under our standard reaction conditions.
We found that p-methyl benzaldehyde was converted to the
corresponding acylal, while acetophenone remained unreacted
(Scheme 2). This examination indicates that aldehydes are more
reactive than ketones most probably due to higher electrophilicity
and less steric hindrance of aldehydes than ketones.
Entry
Solvent
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
9
Solvent-free
IPA
AcOH
MeOH
EtOH
H2O
Toluene
1,4-Dioxane
CHCl3
2
40
45
56
60
75
35
25
23
18
99
62
64
50
65
60
86
90
89
91
10
CH2Cl2
a
Reaction conditions: p-methyl benzaldehyde = 1 mmol, acetic anhydride =
1 mmol, and TSA = 2.5 mol% at room temperature.
TSA at room-temperature (r.t). The product yields were 86%,
91%, 96%, 99%, and 99%, respectively (Table 1, entries 8–12).
Increasing the amount of catalyst beyond 2.5 mol% offered no
further enhancement of the reaction.
We next explored the general applicability of the reaction
conditions employing a catalytic amount of TSA in the synthesis
of acylals from various aromatic, heteroaromatic, and aliphatic
aldehydes (Table 3). Results were obtained within 2–9 min. We
found the reaction to be well-suited to compounds containing
halide, nitro, cyano, methoxy, and ethoxy functionalities. In
the case of hydroxy benzaldehyde and salicylaldehydes the
corresponding triacetates were formed (13–16). It is possible to
monitor the protection reaction of aldehydes using acetic anhydride
visually. In case of aromatic aldehydes a clear solution is observed
upon mixing of the aldehyde and anhydride; addition of the
catalyst to the reaction mixture results in the formation of a solid
In addition to the synthetic process we investigated the
possible deprotection of product acylals within the same catalytic
system by adding water. For this purpose the reaction system
was monitored for 2 h after forming acylal 1 from p-methyl
benzaldehyde without changing conditions. Conversion of the
reaction system from solid to oily liquid in water suggested that
the product acylal is deportected (Scheme 3). The resulting
mixture was examined by NMR spectroscopy without purification.
1
A H NMR spectrum of the resulting mixture before purification
shows a singlet at d 9.91 ppm which is corresponding to an
aldehydic proton. In addition there were no peaks between d 80
and 95 ppm in the 13C NMR spectrum, indicating the absence
of Ar–CH carbon. The new peak at around d 178 ppm clearly
indicates the carbonyl carbon. All of these results show that
aceticanhydride is converted to acetic acid during the deprotec-
tion reaction (Fig. 2).
Table 3 Solvent-free TSA-catalyzed acetylation of various aldehydes with
acetic anhydride at room temperaturea
Entry R in R-CHO
Yield (%) Time (min) m.p. (1C)
1
2
3
4
5
6
7
8
4-Me-C6H4
4-NO2-C6H4
C6H5
4-OMe-C6H4
3,5-OMe-C6H3
3,4,5-OMe-C6H2
4-OEt-C6H4
2-F-4-Br-C6H3
2-Cl-6-F-C6H3
2-Cl-C6H4
99
97
96
95
93
95
96
97
94
97
99
98
93
97
96
96
0
2
5
4
6
8
7
5
5
4
3
2
3
8
5
4
5
10 h
10 h
4
5
3
6
8
8
7
63–65
124–125
43–44
80–82
93–95
111–113
Oil
The performance of TSA compared to that of other recently
reported heterogeneous catalysts for the acylation of aldehydes is
summarized in Table 4. In 2013 Zareyee35 reported the formation of
50–52
92–94
56–57
78–79
81–82
93–94
92–94
65–66
72–74
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9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
2-Br-C6H4
4-Br-C6H4
4-OH-C6H4
2-OH-5-Br-C6H3
2-OH-3-Cl-C6H3
2-OH-3,5-Cl-C6H2
2-OH-4-(CH3)2-N-C6H3
4-(CH3)2-N-C6H4
4-iPr-C6H4
C14H9 (Anthrecene)
C14H9 (Pyrene)
2-Furfural(C4H3O)
Scheme 2 Competitive acylal formation from p-methyl benzaldehyde in
the presence of acetophenone.
0
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Oil
200–202
66–68
51–52
50–52
Oil
95
97
98
98
5-Me-2-Furfural(C4H2O) 96
CH(CH3)2
C5H13
64
63
Oil
a
Scheme 3 TSA-catalyzed cleavage of acylal 1 to p-methyl benzaldehyde
Reaction conditions: p-methyl benzaldehyde = 1 mmol and acetic
in the presence of water.
anhydride = 1 mmol.
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above, TSA as described herein is superior for the high yield
synthesis of acylals, because it requires neither harsh reaction
conditions, additional energy input (i.e., microwave or ultra-
sonication), nor laborious work-up procedures.
Reusability of a catalyst is crucial for large-scale operations
and from an industrial point of view. Therefore, the reusability
of TSA was examined in the synthesis of 1 formed by the
reaction of acetic anhydride with p-methyl benzaldehyde. The
catalyst was effortlessly recovered by adding chloroform to the
reaction mixture. Insoluble TSA was separated by simple filtra-
tion, washed twice with chloroform (20 mL), and dried under
vacuum at 100 1C. The catalyst displayed good reusability after
7 runs (Fig. 3).
Based on the obtained results, the reaction mechanism
might be proposed for the protection of aldehydes with acetic
anhydride in the presence of TSA (Scheme 4). At first p-methyl
benzaldehyde reacts with acidic hydrogen from TSA to form an
intermediate benzylideneoxonium ion which reacts with acetic
anhydride to form an oxonium ion. This oxonium ion under-
goes an intramolecular rearrangement and the proton is rear-
ranged to TSA to form targeted acylals.
The structures of all the compounds were confirmed by IR,
1H and 13C NMR spectroscopies. The IR spectra of compounds
Fig. 2 (A) 1H NMR and (B) 13C NMR spectra of a solution mixture after 2 h
of reaction.
acylals using a nanosilica material (SBA-15-Ph-PrSO3H); the reaction
rate was high, and acetic anhydride was used in excess. Tourani
et al.,18 reported the synthesis of acylals using MCM-41-SO3H,
wherein the heterogeneous catalyst loading was high; the product
yield was low compared to that of TSA. Kannasani et al.36 used
NaHSO4–SiO2 as a supported catalyst at high loading with a
fourfold excess of acetic anhydride; column chromatography was
used for the separation of the acylals. In 2007 Hajipour et al.,37
employed P2O5/Al2O3 as a catalyst for the protection of aldehydes
with acetic anhydride; this procedure required a long time.
Compared to all the heterogeneous acid catalysts mentioned
Fig. 3 Effect of recycling of TSA on the yield of acylal 1.
Table 4 Comparison of various catalysts used for the synthesis of acylal
1a
Time
Entry Catalyst (mg)
Solvent (min) Yield (%) Ref.
1
2
3
4
5
SBA-15Ph-pr-SO3H (1)
MCM-41-SO3H (10)
NaHSO4–SiO2 (25%/wt) Neat
P2O5/Al2O3 (15 mol%) Neat
Neat
Neat
5
3
15
45
2
100
95
94
86
99
31
18
32
33
TSA (2.5 mol%)
Neat
This work
a
Scheme 4 The plausible reaction mechanism for the formation of acylals
Reaction conditions: p-methyl benzaldehyde = 1 mmol and acetic
in presence of TSA.
anhydride = 1 mmol.
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1
1–25 showed the expected regions. In the H NMR spectrum, The chloroform filtrate was evaporated under reduced pressure
the Ar-CH proton signal appeared as a singlet in the region of d and the solid obtained was washed using petroleum ether
9.22–7.56 ppm. The remaining proton signals were observed in (20 mL) three times. Recrystallization from dichloromethane
the expected regions. In the 13C NMR spectra, the Ar-CH carbon afforded the resulting acylal, 1. All known products afforded
signal appeared at d 89.5–83.6 ppm confirms the formation of spectral and physical data consistent with those reported in the
acylals and all known products were identical with those literature. New products were characterized by their IR,
reported in the literature.31 The detailed descriptions of the 1H NMR, and 13C NMR spectra. Detailed descriptions for all
spectral data for all compounds (1–25) are given in the experi- these compounds are given below.
mental section.
4.3. Spectral characterization
4.3.1. p-Tolylmethylenediacetate (1). 99% yield in 2 min
reaction time; solid; H NMR (400 MHz, CDCl3): d (ppm) 7.64
1
3. Conclusions
(s, 1H, Ar–CH), 7.39 (d, J = 7.99 Hz, 2H, Ar–H) 7.19 (d, J =
A straightforward, effective and green procedure for the synthesis of
acylals catalysed by heterogeneous tungstosulfonic solid acid under
neat conditions has been described. This low-cost method has a
number of advantages including use of readily available chemicals,
high yields, neat reaction conditions (solvent-free), and easy work-
up procedures. The procedure provides chemists with a fast and
effective method for preparing diversely substituted acylals. The
TSA catalyst has been fully characterized by FTIR, XRD, and SEM-
EDX to confirm the sulfonation of tungstic acid.
7.99 Hz, 2H, Ar–H), 2.35 (s, 3H, –CH3), 2.09 (s, 6H, –CH3); 13C
NMR (100 MHz, CDCl3): d (ppm) 168.7, 139.7, 132.6, 129.8,
126.5, 89.8, 21.3, 20.8; FTIR (KBr): n = 3428, 1678, 1575,
1418,1319, 754 cmÀ1
.
4.3.2. (4-Nitrophenyl)methylenediacetate (2). 97% yield in
5 min reaction time; solid; 1H NMR (400 MHz, CDCl3): d (ppm)
8.24 (d, J = 8.78 Hz, 2H, Ar–H),7.70 (s, 1H, Ar–CH), 7.67 (d, J = 8.
84 Hz, 2H, Ar–H), 2.13 (s, 6H, –CH3); 13C NMR (100 MHz,
CDCl3): d (ppm) 168.5, 148.6, 141.8, 127.8, 123.8, 88.3, 20.7;
FTIR (KBr): n = 3495, 3124, 1762, 1529, 1431, 1251, 856 cmÀ1
.
4.3.3. Phenylmethylenediacetate (3). 96% yield in 4 min
reaction time; solid; H NMR (400 MHz, CDCl3): d (ppm) 7.66
4. Experimental
4.1. General
1
(s, 1H, Ar–CH), 7.48–7.32 (m, 5H, Ar–H), 2.02 (s, 6H, –CH3);
13C NMR (100 MHz, CDCl3): d (ppm) 168.6, 135.5, 129.6,
128.5, 126.6, 89.6, 20.6; FTIR (KBr): n = 3434, 1690, 1590,
The various substituted aldehydes were purchased from Sigma
Aldrich Co. (St. Louis, MO, USA), tungstic acid (TA) and chloro
sulfonic acid (Yakuri Pure Chemical Co., Japan). All experiments
were carried out under solvent-free conditions. Analytical thin layer
chromatography (TLC) was carried out in an ethyl acetate/n-hexane
(8/2) mixture on pre-coated silica gel plates (Merck Chem.,
Germany) and developed by use of iodine. Fourier transform
infrared (FT-IR) spectra were recorded on a Shimadzu IR Prestige
21 spectrometer at room temperature. The samples were analyzed
as KBr discs in the range of 3500–500 cmÀ1. The 1H NMR
(400 MHz) and 13C NMR (100 MHz) spectra were recorded on a
Varian INOVA 400 NMR spectrometer at room temperature.
Chemical shift values are reported relative to tetramethylsilane
(TMS, Me4Si). The data are presented as follows: chemical shift
(ppm), multiplicity (s = singlet, d = doublet, m = multiplet), and
coupling constant, J (Hz). The XRD analysis was performed by
use of an automatic Philips powder diffractometer with nickel-
filtered Cu Ka radiation. The diffraction pattern was collected
in the 2y range of 0–801 in steps of 0.021 with counting times of
2 s stepÀ1. The microstructures of the samples and the energy
dispersive X-ray spectra (EDX) were investigated by use of an
S-3000 scanning electron microscope (SEM; Hitachi, Japan).
1438, 1046 cmÀ1
.
4.3.4. (4-Methoxyphenyl)methylenediacetate (4). 95% yield
in 8 min reaction time; solid; 1H NMR (400 MHz, CDCl3): d
(ppm) 7.61 (s, 1H, Ar–CH), 7.44 (d, J = 8.73 Hz, 2H, Ar–H), 6.90
(d, J = 8.84 Hz, 2H, Ar–H), 3.80 (s, 3H, –OCH3), 2.09 (s, 6H,
–CH3); 13C NMR (100 MHz, CDCl3): d (ppm) 168.7, 160.6, 131.9,
128.2, 113.9, 89.7, 55.3, 20.9; FTIR (KBr): n = 3431, 3099, 1703,
1405, 1250 cmÀ1
.
4.3.5. (3,5-Dimethoxyphenyl)methylenediacetate (5). 93%
yield in 8 min reaction time; solid; 1H NMR (400 MHz, CDCl3):
d (ppm) 7.58 (s, 1H, Ar–CH), 6.64 (d, J = 2.32 Hz, 2H, Ar–H), 6.46
(t, J = 2.31 Hz, 1H, Ar–H), 3.78 (s, 6H,–OCH3) 2.10 (s, 6H, –CH3);
13C NMR (100 MHz, CDCl3): d (ppm) 168.8, 160.9, 137.5, 107.1,
104.6, 101.6, 89.4, 55.4, 20.8; FTIR (KBr): n = 3428, 2975, 1678,
1575, 1319, 754 cmÀ1
.
4.3.6. (3,4,5-Trimethoxyphenyl)methylenediacetate (6). 95%
yield in 7 min reaction time; solid; 1H NMR (400 MHz, CDCl3): d
(ppm) 7.57 (s, 1H, Ar–CH), 6.73 (s, 2H, Ar–H), 3.86 (s, 9H,–
(OCH3)3), 2.11 (s, 6H, –CH3); 13C NMR (100 MHz, CDCl3): d (ppm)
168.7, 153.3, 139.0, 130.8, 103.8, 89.7, 60.7, 56.1, 20.8; FTIR
(KBr): n = 3435, 2941, 1687, 1587, 1330 cmÀ1
4.3.7. (4-Ethoxyphenyl)methylenediacetate (7). 96% yield
.
4.2. General procedure for the synthesis of acylals 1–25
In a 50 mL round bottom flask TSA (2.5 mol%) was added to a in 5 min reaction time; Liquid; 1H NMR (400 MHz, CDCl3):
mixture of p-methyl benzaldehyde (1 mmol) and acetic anhydride d (ppm) 7.59 (s, 1H, Ar–CH), 7.41 (d, J = 8.8 Hz, 2H, Ar–H), 6.88
(1 mmol). The reaction mixture was stirred at room temperature, (d, J = 8.8 Hz, 2H, Ar–H), 4.13–3.97 (m, 2H, –OCH2), 2.08 (s, 6H,
becoming solid within 2 min. Chloroform was added, and the –CH3), 1.39 (t, J = 7.0 Hz, 3H, –CH3); 13C NMR (100 MHz,
insoluble catalyst was separated by simple filtration, washed CDCl3): d (ppm) 168.8, 159.9, 128.0, 127.5, 114.4, 89.7, 63.5,
twice with chloroform, and dried at 100 1C for 2 h for reuse. 20.8, 14.7; FTIR (neat): n = 3369, 2982, 1678, 1312, 1042 cmÀ1
.
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4.3.8. (4-Bromo-2-fluorophenyl)methylenediacetate (8). 97% 131.1, 129.1, 126.4, 109.9, 84.3, 20.6, 20.2; FTIR (KBr): n = 3431,
yield in 5 min reaction time; solid; 1H NMR (400 MHz, CDCl3): d 2875, 1672, 1274, 829,700 cmÀ1
(ppm) 7.81 (s, 1H, Ar–CH), 7.40–7.26 (m, 3H, Ar–H), 2.10 (s, 6H, 4.3.17. (4-(Dimethylamino)-2-hydroxyphenyl)methylene-
–CH3); 13C NMR (100 MHz, CDCl3): d (ppm) 168.2, 161.2, 129.2, diacetate (17). Corresponding acylals not formed.
.
127.6, 124.3, 122.3, 119.5, 85.0, 20.6; FTIR (KBr): n = 3462, 1762,
1604, 1373, 1127, 772, 632 cmÀ1
4.3.9. (4-Chloro-6-fluorophenyl)methylenediacetate (9). 94%
4.3.18. (4-(Dimethylamino)phenyl)methylenediacetate (18).
Corresponding acylals not formed.
.
4.3.19. (4-(Isopropyl phenyl)methylenediacetate (19). 95%
yield in 4 min reaction time; solid; 1H NMR (400 MHz, CDCl3): d yield in 4 min reaction time; Liquid; 1H NMR (400 MHz, CDCl3):
(ppm) 8.09 (s, 1H, Ar–CH), 7.29–6.99 (m, 3H, Ar–H), 2.10 (s, 6H, d (ppm) 7.80 (s, 1H, Ar–CH), 7.40 (d, J = 7.4 Hz, 2H, Ar–H), 7.37
–CH3); 13C NMR (100 MHz, CDCl3): d (ppm) 168.5, 162.9, 134.5, (d, J = 7.4 Hz, 2H, Ar–H), 3.19–2.98 (m, 1H,–CH), 2.09 (s, 6H,
131.5, 125.9, 121.3, 115.1, 86.0, 20.6; FTIR (KBr): n = 3434, –CH3), 1.75 (d, J = 6.4 Hz, 6H,–CH3),); 13C NMR (100 MHz,
2988,1690, 1408, 1315, 1046, 814, 714 cmÀ1
.
CDCl3): d (ppm) 168.4, 148.2, 127.1, 122.4, 85.2, 32.4, 21.5, 20.2;
4.3.10. (2-Chlorophenyl)methylenediacetate (10). 97% yield FTIR (neat): n = 2342, 1785, 1648, 1136, 1032 cmÀ1
.
in 3 min reaction time; solid; 1H NMR (400 MHz, CDCl3): d
4.3.20. Anthrene-9-ylmethylenediacetate (20). 97% yield in
(ppm) 7.96 (s, 1H, Ar–CH), 7.56–7.30 (m, 4H, Ar–H), 2.13 (s, 6H, 5 min reaction time; solid; 1H NMR (400 MHz, CDCl3): d (ppm)
–CH3); 13C NMR (100 MHz, CDCl3): d (ppm) 168.3, 133.2, 130.8, 9.22 (s, 1H, Ar–CH), 8.68 (d, J = 8.9 Hz, 2H, Ar–H), 8.51 (s, 1H,
129.9, 127.6, 126.9, 87.1, 20.7; FTIR (KBr): n = 3434, 2968, 1690, Ar–H), 8.01 (d, J = 8.9 Hz, 2H, Ar–H), 7.60–7.46 (m, 4H, Ar–H),
1409, 1267, 744, 558 cmÀ1
.
2.10 (s, 6H, –CH3); 13C NMR (100 MHz, CDCl3): d (ppm) 168.9,
4.3.11. (2-Bromophenyl)methylenediacetate (11). 99% yield in 131.3, 130.5, 129.9, 128.9, 126.6, 125.6, 125.3, 125.0, 87.4, 20.8;
2 min reaction time; solid; 1H NMR (400 MHz, CDCl3): d (ppm) 7.89 FTIR (KBr): n = 3462, 1762, 1373, 1245, 942, 590 cmÀ1
.
(s, 1H, Ar–CH), 7.58–7.52 (m, 2H, Ar–H), 7.37–7.33 (m, 1H, Ar–H),
4.3.21. Pyren-1-ylmethylenediacetate (21). 98% yield in
7.27–7.23 (m, 1H, Ar–H), 2.13 (s, 6H, –CH3); 13C NMR (100 MHz, 3 min reaction time; solid; 1H NMR (400 MHz, CDCl3):
CDCl3): d (ppm) 168.3, 134.8, 133.1, 131.0,127.8, 127.5, 122.5, 89.1, d (ppm) 8.56 (s, 1H, Ar–CH), 8.54–8.00 (m, 9H, Ar–H), 2.16
20.7; FTIR (KBr): n = 3477, 3053, 1759, 1373, 687, 553 cmÀ1
.
(s, 6H, –CH3); 13C NMR (100 MHz, CDCl3): d (ppm) 168.8, 132.4,
4.3.12. (4-Bromophenyl)methylenediacetate (12). 98% yield 131.1, 130.4, 128.6, 128.5, 128.3, 128.0, 127.1, 126.1, 125.7,
in 3 min reaction time; solid; 1H NMR (400 MHz, CDCl3): d 125.6, 125.2, 124.8, 124.5, 122.9, 89.5, 20.9, 89.5, 20.9; FTIR
(ppm) 7.60 (s, 1H, Ar–CH), 7.52 (d, J = 8.55 Hz, 2H, Ar–H), 7.37 (KBr): n = 3431, 3036, 1675, 1373, 834, 709 cmÀ1
.
(d, J = 8.23 Hz, 2H, Ar–H), 2.10 (s, 6H, –CH3); 13C NMR (100 MHz,
CDCl3): d (ppm) 168.6, 134.5, 131.8, 128.4, 123.9, 89.1, 20.8; FTIR 6 min reaction time; solid; 1H NMR (400 MHz, CDCl3): d
(KBr): n = 3473, 3093, 1756, 1690, 1372, 756, 601 cmÀ1
(ppm) 7.69 (s, 1H, Ar–CH), 7.43 (t, J = 0.8 Hz, 1H, Ar–H), 6.49
4.3.22. Furan-2yl-methylenediacetate (22). 98% yield in
.
4.3.13. (4-Hydroxyphenyl)methylenediacetate (13). 93% yield (d, J = 1.2 Hz, 1H, Ar–H), 6.37–6.36 (m, 1H, Ar–H), 2.10 (s, 6H,
in 8 min reaction time; solid; 1H NMR (400 MHz, CDCl3): d –CH3); 13C NMR (100 MHz, CDCl3): d (ppm) 168.4, 147.8, 143.6,
(ppm) 7.65 (s, 1H, Ar–CH), 7.51 (d, J = 8.68 Hz, 2H, Ar–H), 7.10 110.3, 109.7, 83.5, 20.7; FTIR (KBr): n = 3347, 3129, 2213, 1723,
(d, J = 8.58 Hz, 2H, Ar–H), 2.28 (s, 3H, –CH3), 2.1 (s, 6H, –CH3); 13
NMR (100 MHz, CDCl3): d (ppm) 169.2, 168.6, 151.5, 133.1, 128.0,
121.8,89.2, 21.1, 20.8; FTIR (KBr): n = 3253, 2829, 1673, 1446, 1384, yield in 8 min reaction time; solid; 1H NMR (400 MHz, CDCl3):
835, 605 cmÀ1
d (ppm) 7.582 (s, 1H, Ar–CH), 7.09 (d, J = 3.6 Hz, 1H, Ar–H), 6.42
4.3.14. (5-Bromo-2-hydroxyphenyl)methylenediacetate (14). (d, J = 3.2 Hz, 1H, Ar–H), 2.32 (s, 3H,–CH3) 2.08 (s, 6H, –CH3); 13
97% yield in 5 min reaction time; solid; 1H NMR (400 MHz, NMR (100 MHz, CDCl3): d (ppm) 168.6, 152.2, 144.8, 110.2, 107.3,
CDCl3): d (ppm) 7.83 (s, 1H, Ar–CH), 7.68 (d, J = 8.8 Hz, 1H, Ar–H) 83.8, 20.1, 14.2; FTIR (KBr): n = 3089, 1644, 1482, 1341, 685 cmÀ1
C
1029, 800, 681 cmÀ1
.
4.3.23. (5-Methylfuran-2yl)methylenediacetate (23). 96%
.
C
.
7.52–7.39 (m, 1H, Ar–H) 7.09 (d, J = 8.8 Hz, 1H, Ar–H), 2.29 (s, 3H,
4.3.24. 2-Methylpropane-1,1-diyl diacetate (24). 64% yield
1
–CH3), 2.06 (s, 6H, –CH3); 13C NMR (100 MHz, CDCl3): d (ppm) in 8 min reaction time; Liquid; H NMR (400 MHz, CDCl3): d
168.5, 168.0, 146.5, 133.4, 130.5, 128.7, 123.7, 109.2, 84.5, 20.8, (ppm) 6.62 (d, J = 5.6 Hz, 1H,–CH), 2.09 (s, 6H,–CH3), 1.19 (m,
20.5; FTIR (KBr): n = 2242, 1825, 1648, 1356, 1152 cmÀ1
.
1H, –CH), 0.72 (d, J = 8.6 Hz, 6H,–CH3); FTIR (neat): n = 2862,
4.3.15. (3-Chloro-2-hydroxyphenyl)methylenediacetate (15). 1465, 1392, 1241, 725 cmÀ1
96% yield in 4 min reaction time; solid; 1H NMR (400 MHz,
.
4.3.25. Hexane-1,1-diyl diacetate (25). 63% yield in 7 min
CDCl3): d (ppm) 7.83 (s, 1H, Ar–CH), 7.53–7.46 (m, 3H, Ar–H), reaction time; Liquid; 1H NMR (400 MHz, CDCl3): d (ppm) 6.11
2.36 (s, 3H,–CH3), 2.08 (s, 6H, –CH3); 13C NMR (100 MHz, (t, J = 5.6 Hz 1H, –CH), 2.08 (s, 6H, –CH3), 1.89–1.09 (m,
CDCl3): d (ppm) 168.2, 145.1, 131.4, 130.3, 128.2, 126.9, 126.2, 8H,(CH2)4), 0.79 (t, J = 6.2 Hz, 3H, –CH3); FTIR (neat): n =
85.2, 20.6, 20.3; FTIR (KBr): n = 3473, 2999, 1748, 1487, 1219, 2874, 1826, 1452, 1261,1245, 1120, 676 cmÀ1
.
755 cmÀ1
.
4.3.16. (3,5-Dichloro-2-hydroxyphenyl)methylenediacetate (16).
96% yield in 5 min reaction time; solid; 1H NMR (400 MHz, CDCl3):
d (ppm) 7.79 (s, 1H, Ar–CH), 7.50 (d, J = 2.4 Hz, 1H, Ar–H),7.47
Acknowledgements
(d, J = 2.4 Hz, 1H, Ar–H), 2.35 (s, 3H,–CH3), 2.09 (s, 6H, –CH3); This work was supported by the Fusion Research Program for
13C NMR (100 MHz, CDCl3): d (ppm) 168.0, 143.7, 132.1, 131.4, Green Technologies through the National Research Foundation
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Paper
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of Korea funded by the Ministry of Science, ICT and Future
Planning (2012M3C1A1054502) and the Basic Science Research
Program through the National Research Foundation of Korea
(2015R1D1A1A09057372). The authors also thank the BK21
PLUS Program for partial financial support.
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