Simple synthesis of geminal diacetates (Acylals) of aromatic aldehydes

Article abstract of DOI:10.1080/00397910500514154

The geminal diacetates of aromatic aldehydes were prepared from corresponding aldehydes by refluxing with acetic anhydride without any catalysts or even any additional solvent. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910500514154

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Simple Synthesis of Geminal Diacetates
(
Acylals) of Aromatic Aldehydes
a
a
Yurngdong Jahng & Motiur A. F. M. Rahman
a
College of Pharmacy, Yeungnam University, Gyongsan, Korea
Published online: 24 Feb 2007.
To cite this article: Yurngdong Jahng & Motiur A. F. M. Rahman (2006) Simple Synthesis of Geminal
Diacetates (Acylals) of Aromatic Aldehydes, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 36:9, 1213-1220
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Synthetic Communications , 36: 1213–1220, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500514154
Simple Synthesis of Geminal Diacetates
(Acylals) of Aromatic Aldehydes
Motiur A. F. M. Rahman and Yurngdong Jahng
College of Pharmacy, Yeungnam University, Gyongsan, Korea
Abstract: The geminal diacetates of aromatic aldehydes were prepared from corre-
sponding aldehydes by refluxing with acetic anhydride without any catalysts or even
any additional solvent.
Keywords: Aldehydes, geminal diacetate, solvent-free conditions
INTRODUCTION
Merits of geminal diacetate (acylal) as an useful protecting group for carbonyl
[1]
compounds stem from not only its stability in neutral and basic media as
[3–7]
[2]
well as toward aqueous acids but also its ease of deprotection.
Additionally, geminal diacetates are stable toward a variety of reactions.
Thus, geminal diacetates have been used as important building blocks for
[
8–13]
aldehydes and have played important roles in organic synthesis.
aration of geminal diacetates was, generally, achieved by the reaction of
Prep-
[14]
aldehyde under the catalysis of strong protic acid such as H SO ,
2
4
[
15]
[16]
[17]
H PO ,
3
perchloric acids,
and sulfonic acids,
although the yields
4
were considerably poor and the required reaction time quite long. Lewis
[
2,15]
[18]
[15]
[15]
[15]
[22]
[27]
acids such as FeCl ,
3
FeCl /SiO ,
2
SnCl2,
[25]
InCl3,
FeSO4,
[15]
CuSO ,
ZnCl2,
[21]
CoCl2,
ZnSO4,
PCl3,
3
[
19]
[20]
[15]
Zn(BF ) ,
4
BF3,
WCl6,
2
4
[
23]
[24]
[26]
.
TMSCl NaI,
.
and Zr(SO4)2 4H O/SiO
2 2
InBr3,
replaced protic acids and improved the yields substantially. Additionally,
Received in Japan July 28, 2005
Address correspondence to Yurngdong Jahng, College of Pharmacy, Yeungnam
University, Gyongsan 712-749, Korea. Tel.: 82-53-810-2821; Fax: 82-53-811-3871;
E-mail: ydjahng@yumail.ac.kr
1
213

1
214
M. A. F. M. Rahman and Y. Jahng
[
28]
[29]
[30]
[31]
P O ,
2
P O /SiO ,
I ,
2
NBS,
and various metal salts such as
[36]
5
2
5
2
[32]
[33]
[34]
AlPW O , Bi(OTf) xH O, Bi(NO ) 5H O, Cu(OTf)2, LiBF4,
[35]
.
.
1
2
40
3
2
[38]
3 3
[39]
2
[
37]
[40]
.
LiOTf, Mo/TiO2 ZrO , Se(OTf)3, Zr–sulfophenyl phosphonate,
.
and H P W O 24H O
2
[
41]
were introduced to improve yield as well as
6
2
18 62
2
[
42]
reduce reaction time. Solid acidic materials Nafion-H,
[
and HZSM-5,
tungstosilicic acid
[47]
Amberlyst-15,
43]
[44]
[45]
[46]
Y-zeolite,
P O –montmorillonite K-10,
b-zeolite,
graphite,
[49]
[
48]
[50]
Zn/Yb(OTf)3,
Fe(III)–montmorillonite,
Zn–montmorillonite,
[52]
2
5
[
51]
and PVC–FeCl complex
3
were additionally
introduced as catalysts, most of which employed solvent-free reaction con-
ditions. Nevertheless, up to this point the development of procedures for the
preparation of geminal diacetates relied on the use of rather strong acids
and toxic and/or expensive reagents, which led continuing interests to
develop an efficient procedure and/or catalyst. We herein describe a simple
and efficient procedure for the preparation of geminal diacetates.
RESULTS AND DISCUSSION
In this communication we disclose the reaction of aldehyde with acetic
anhydride to afford corresponding geminal diacetates. Reaction proceeds
without any additional catalyst, reagent, or solvent. Methyl ether and
methythio ether moieties were not influenced under the reaction condition.
Although the reaction of benzaldehyde with Ac O in acetonitrile was pre-
2
[34]
viously examined but failed to provide the corresponding 1,1-diacetate,
we successively isolated benzaldehyde-1,1-diacetate in 85% yield. Although
low yield (4%) was reported for 4-nitrobenzaldehyde even in the presence
[
22]
of a catalyst,
corresponding 1,1-diacetates in 82–93%.
all three isomers (compounds 4, 8, and 12) yielded
Although a variety of aldehydes were converted into the corresponding
geminal diacetates in good yields (Table 1), we failed to convert 2-chloro-
benzaldehyde to its 1,1-diacetae. The reason remains to be explored.
The present method is a simple and efficient procedure for the preparation
of geminal diacetates of aromatic aldehydes. In addition, this procedure does
not employ any halogenated solvents, additional additives, and/or catalysts,
which are important from the economical and environmental point of view.
In conclusion, a simple and efficient procedure for the preparation of
geminal diacetates was established. The method has advantages over pre-
viously described methods in yield, simplicity of operation, and economical
as well as environmental aspects.
EXPERIMENTAL
Melting points were determined on a Fisher-Jones melting-point apparatus
and are uncorrected. Infrared spectra were recorded using KBr pellets for
solids and neat for liquids on a Perkin-Elmer 1330 grating spectrometer.

Geminal Diacetates (Acylals)
1215
Table 1. Preparation of geminal diacetates from aldehdyes
a
a,b
Entry
R
Time (h)
Yield (%)
Mp (8C)
[
14]
1
2
3
4
5
6
7
8
9
H
2-F
1.5
3.5
4
85
82
73
85
78
75
79
93
74
65
82
82
70
71
83
43–44 (45.8
)
27
80
2-Br
2-NO2
3-F
[
[
22]
22]
6
92 (91–92
30–31
65 (65–66
)
)
2
3-Cl
3-Br
3
4
Thick liquid
[
2]
3-NO
4-F
2
5.5
2
63 (64–66
39
)
[
53]
10
11
12
13
14
15
4-Cl
4-Br
4-NO
3
84–85 (80–81
85
)
4
[
13]
2
5.5
1
121 (125–126
50
)
4-SCH
3
[
13]
4-OCH3
3,5-Di(OMe),4-OAc
1.5
3
65 (64–65
125–127
)
a
Reaction time and yields are not maximized. In most cases, the value given is from a
single experiment.
b
All yields refer to pure isolated products.
NMR spectra were obtained using a Bruker-250 spectrometer (250 MHz for
1
13
H NMR and 62.5 MHz for C NMR) and are reported as parts per million
ppm) from the internal standard of tetramethylsilane. Column chromato-
(
graphy was carried out on 60–120-mesh Merck silica gel. Chemicals and
solvents were commercial reagent grade and were used without further
purification.
General Procedure for the Preparation of Acylals
A mixture of aldehyde (1.00 mmol) and acetic anhydride (10 mL) was refluxed
for 1–6 h. The reaction was monitored by TLC. After the given reaction time,
the reaction mixture was poured into 5% aq. NaOH. The resulting mixture was
extracted with CH Cl (30 mL ꢀ 3). Combined organic layers were washed
2
2
successively with water and dried over anhydrous MgSO . The solvent was
4

1
216
M. A. F. M. Rahman and Y. Jahng
evaporated under reduced pressure to provide crude product, which was chro-
matographed on silica gel eluting with CH Cl : n-hexane (1 : 1). The early
2
2
fractions afforded the desired geminal diacetates pure enough for the
analysis. Spectral data of the unreported compounds are as follows.
1
2
-Fluorobenz-aldehyde-1,1-diacetate (2b). Mp 278C: H NMR (CDCl ,
3
2
50 MHz) d 7.88 (s, 1H), 7.53–7.47 (td, J ¼ 7.5, 1.6 Hz, 1H), 7.40–7.31
(
(
(
(
(
m, 1H), 7.18–7.12 (t, J ¼ 7.5 Hz, 1H), 7.06 (td, J ¼ 9.6, 0.8 Hz, 1H), 2.10
1
3
s, 6H).
JC-F ¼ 249.1 Hz), 131.40 (J ¼ 8.3 Hz), 127.93 (J ¼ 3.0 Hz), 124.14
C NMR (CDCl , 62.5 MHz) d 168.32 (C 55 O), 160.10
3
C-F
C-F
JC-F ¼ 4.3 Hz), 122.90 (J ¼ 12.4 Hz), 115.85 (J ¼ 20.8 Hz), 85.33
C-F
C-F
JC-F ¼ 3.8 Hz), 20.61.
1
2
-Bromobenzaldehyde-1,1-diacetate (2c). Mp 808C: H NMR (CDCl3,
2
50 MHz) d 7.88 (s, 1H), 7.55 (overlapped td, J ¼ 7.7, 1.2 Hz, 2H), 7.34
1
3
(
td, J ¼ 7.7, 2.0 Hz, 1H), 7.24 (td, J ¼ 7.6, 1.6 Hz, 1H), 2.12 (s, 6H).
C
NMR (CDCl , 62.5 MHz) d 168.32, 134.77, 133.14, 131.03, 127.80, 127.56,
3
122.45, 88.96 20.64.
1
3
2
7
6
-Fluorobenzaldehyde-1,1-diacetate (2e). Mp 30–318C: H NMR (CDCl ,
3
50 MHz) d 7.64 (s, 1H), 7.40–7.31 (m, 1H), 7.29 (t, J ¼ 1H, H2),
1
3
.26–7.20 (m, 1H), 7.11–7.03 (m, 1H), 2.11 (s, 6H). C NMR (CDCl ,
3
2.5 MHz)
d
168.55 (C 55 O), 162.60 (JC-F ¼ 245.4 Hz), 137.72
C-F C-F
(
JC-F ¼ 7.3 Hz), 130.20 (J ¼ 8.0 Hz), 122.35 (J ¼ 6.1 Hz), 116.61
C-F C-F
(
JC-F ¼ 21 Hz), 113.60 (J ¼ 22.8 Hz), 88.67 (J ¼ 1.8 Hz), 20.65.
1
3
2
0
-Bromobenzaldehyde-1,1-diacetate (2g). Thick oil: H NMR (CDCl3,
50 MHz) d 7.64 (s, J ¼ 1.5 Hz, H2), 7.60 (s, 1H), 7.50 (dd, J ¼ 7.9,
.7 Hz, H6), 7.42 (d, J ¼ 7.7 Hz, H4), 7.24 (t, J ¼ 7.8 Hz, H5), 2.10 (s, 6H).
1
3
C NMR (CDCl ) d 168.55 (C 55 O), 137.48, 132.73, 130.11, 129.64,
3
125.37, 122.48, 88.63, 20.70.
1
4
-Fluorobenzaldehyde-1,1-diacetate (2i). Mp 398C: H NMR (CDCl3,
2
50 MHz) d 7.61 (s, 1H), 7.48 (ddd, J ¼ 8.6, 5.3, 1.9 Hz, 2H), 7.04 (dm,
1
3
J ¼ 8.7 Hz, 2H), 2.08 (s, 6H). C NMR (CDCl , 62.5 MHz) d 168.60
3
(
C 55 O), 163.27 (J ¼ 247.3 Hz), 131.43 (JC-F ¼ 3.2 Hz), 128.64
C-F
(JC-F ¼ 8.6 Hz), 115.47 (JC-F ¼ 21.8 Hz), 89.04, 20.66.
1
4
2
2
1
-Bromobenzaldehyde-1,1-diacetate (2k). Mp 858C: H NMR (CDCl3,
50 MHz) d 7.60 (s, 1H), 7.52 (dm, J ¼ 8.4 Hz, 2H), 7.37 (dm, J ¼ 8.4 Hz,
1
H), 2.10 (s, 6H). C NMR (CDCl , 62.5 MHz) d 168.65 (C 55 O), 134.45,
3
3
31.78, 128.39, 123.94, 89.01, 20.80.
1
4
-Methylthiobenzaldehyde-1,1-diacetate (2m). Mp 508C: H NMR (CDCl ,
3
250 MHz) d 7.62 (s, 1H), 7.43 (d, J ¼ 8.4 Hz, 2H), 7.26 (d, J ¼ 8.3 Hz, 2H),

Geminal Diacetates (Acylals)
1217
1
.48 (s, S-CH , 3H), 2.11 (s, 6H). C NMR (CDCl , 62.5 MHz) d 168.75
3
2
3
3
(C 55 O), 140.84, 131.99, 127.14, 126.09, 89.54, 20.87, 15.41.
3
,5-Dimethoxy-4-acetoxybenzaldehyde-1,1-diacetate (2o). Mp 125–1278C:
1
H NMR (CDCl , 250 MHz) d 7.60 (s, 1H), 6.76 (s, 2H,), 3.82 (s, –OCH ꢀ 2,
3
3
1
3
6
6
2
H), 2.31 (s, –OCOCH , 3H), 2.10 (s, –COCH ꢀ 2, 6H). C NMR (CDCl ,
3
3
3
2.5 MHz) d 168.62, 168.50, 152.21, 133.59, 129.80, 103.47, 89.43, 56.20,
0.86, 20.41.
ACKNOWLEDGMENT
Support from Korean Research Foundation (Grant KRF-2004-005-E00004) is
gratefully acknowledged.
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