One-pot catalytic conversion of epoxides to 1,2-diacetates with hydride transferring agents in acetic anhydride

Article abstract of DOI:10.1080/00397911003629515

Direct transformation of structurally different epoxides to the corresponding 1,2-diacetates was studied with catalytic amounts of NaBH ₄, LiAlH₄, CaH₂, and NaH. The reactions were carried out in refluxing acetic anhydride within 1.5-2.5h to give vic-diacetates in good to excellent yields. Conversion of R-(+)-styrene oxide to S-(+)-1,2-diacetoxy-1-phenylethane was carried out with good yield and stereospecificity with the NaBH₄/Ac₂O system at 0°C.

Full text of DOI:10.1080/00397911003629515

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One-Pot Catalytic Conversion of
Epoxides to 1,2-Diacetates with Hydride
Transferring Agents in Acetic Anhydride
a
a
Behzad Zeynizadeh & Leila Sadighnia
a
Faculty of Science, Department of Chemistry, Urmia University,
Urmia, Iran
Published online: 31 Jan 2011.
To cite this article: Behzad Zeynizadeh & Leila Sadighnia (2011) One-Pot Catalytic Conversion
of Epoxides to 1,2-Diacetates with Hydride Transferring Agents in Acetic Anhydride, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
41:5, 637-644
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1
Synthetic Communications , 41: 637–644, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911003629515
ONE-POT CATALYTIC CONVERSION OF EPOXIDES
TO 1,2-DIACETATES WITH HYDRIDE TRANSFERRING
AGENTS IN ACETIC ANHYDRIDE
Behzad Zeynizadeh and Leila Sadighnia
Faculty of Science, Department of Chemistry, Urmia University, Urmia, Iran
Abstract Direct transformation of structurally different epoxides to the corresponding
1,2-diacetates was studied with catalytic amounts of NaBH , LiAlH , CaH , and
4 4 2
NaH. The reactions were carried out in refluxing acetic anhydride within 1.5–2.5 h to
give vic-diacetates in good to excellent yields. Conversion of R-(þ)-styrene oxide to
S-(þ)-1,2-diacetoxy-1-phenylethane was carried out with good yield and stereospecifi-
ꢀ
city with the NaBH
4
/Ac
2
O system at 0 C.
2 4 4
Keywords CaH ; 1,2-diacetate; epoxide; LiAlH ; NaBH ; NaH
The ring strain and polarization of carbon–oxygen bonds make epoxides important
[
1–3]
and versatile synthetic intermediates in organic synthesis.
Nucleophilic ring
opening of epoxides with water to give the corresponding 1,2-diols is one of the most
useful reactions, and the subsequent acetylation of alcohols provides an efficient
means for the protection of hydroxyl groups and preparation of 1,2-diacetoxy
[
4]
esters. Therefore, direct transformation of epoxides into the corresponding 1,2-
diacetates is an important reaction. The literature review shows that this transform-
ation has been achieved with the reaction of epoxides and acetic anhydride in
[
2
[8]
5]
[6]
the presence of HCl, ZnCl , (n-Bu) NOAc, 1,8-diazabicyclo[5.4.0]-undec-7-ene
4
[7]
[9]
[10]
(
DBU)–LiCl, BF ꢁ Et O, R POAc, tertiary amine–carboxylic acid,
HY
(TBA) PFeW O ꢁ
3
[12]
2
4
[13]
[
11]
[14]
zeolite,
H O,
2
Bu P,
3
LiClO4
Er(OTf) ,
3
(NH ) (PMo O ) ,
4 3
12 40 6
[17]
4
11 39
[
15]
[16]
3 and phosphomolybdic acid.
protocols suffer from using unavailable, expensive, or hazardous reagents, strongly
However, most of the reported
Received November 13, 2009.
Address correspondence to Behzad Zeynizadeh, Faculty of Science, Department of Chemistry,
Urmia University, Urmia 57159-165, Iran. E-mail: bzeynizadeh@gmail.com
6
37

638
B. ZEYNIZADEH AND L. SADIGHNIA
Scheme 1. Conversion of epoxides to 1,2-diacetates with hydride transferring agents.
acidic=basic reaction conditions, extended reaction times, and limitation to use a
wide range of epoxides. So, the development and introduction of convenient
methods using cheap and commercially available reagents is of practical interest
and is still in demand.
In this context, we report a catalytic method for one-pot conversion of
structurally different epoxides to the corresponding 1,2-diacetates with hydride
transferring agents such as NaBH , LiAlH , CaH and NaH in refluxing acetic
4
4
2,
anhydride (Scheme 1).
Continuation of our research program in the nucleophilic ring opening of
epoxides and reduction of functional groups with NaBH encouraged us to study
4
the capability of sodium borohydride for hydridic ring opening of epoxides. A pre-
liminary experiment showed that the reaction of styrene oxide (1 mmol) as a model
compound with NaBH (1 mmol) in CH Cl , tetrahydrofuran (THF), CH CN, and
4
2
2
3
i-PrOH failed to form any product. However, the reaction in refluxing acetic anhy-
dride unexpectedly produced 1,2-diacetoxy-1-phenylethane in 96% yield within
2
lytic amounts of NaBH (0.2 mmol) within 1.5 h. In addition, with 0.15 or 0.1 mmol
5 min. More experiments showed that the reaction can be also carried out with cata-
4
of NaBH , the reaction took a long time or did not complete after 5 h, respectively
4
(Table 1). Encouraged by the result, the usefulness of this synthetic method was stud-
ied more with the reaction of structurally different epoxides under the optimized
conditions (Table 1, entry 6). The results of this investigation are summarized in
Table 2. All reactions were carried out perfectly in good to excellent yields within
1
.5–2.5 h.
We also observed that conversion of R-(þ)-styrene oxide to S-(þ)-1,2-
diacetoxy-1-phenylethane was carried out with good yield and stereospecificity
(
Scheme 2). When we reacted optically active R-(þ)-styrene oxide with 0.2 molar
ꢀ
equivalents of NaBH at 0 C in acetic anhydride, S-(þ)-1,2-diacetoxy-1-pheny-
4
lethane was obtained in 95% yield and 92% optical purity. The optical purity of
Table 1. Conversion of styrene oxide to 1,2-diacetoxy-1-phenylethane under different conditions
Entry
Molar ratio epoxide=NaBH
4
Condition
Time (h)
Conversion (%)
1
2
3
4
5
6
7
8
1:2
1:2
CH
2
Cl
2
(2 mL), room temp.
3
2
0
0
THF (2 mL), reflux
CH CN (2 mL), reflux
i-PrOH (2 mL), reflux
1:2
1:2
3
2
0
2
0
1:1
Ac
Ac
Ac
Ac
2
2
2
2
O (1 mL), reflux
O (1 mL), reflux
O (1 mL), reflux
O (1 mL), reflux
0.42
1.5
3
100
100
100
65
1:0.2
1:0.15
1:0.1
5

CONVERSION OF EPOXIDES TO 1,2-DIACETATES
639
a
Table 2. One-pot conversion of epoxides to the corresponding 1,2-diacetates with NaBH
4
b
Entry
1
Epoxide (a)
Product (b)
Time (h) Yield (%)
Ref.
1.5
2
96
98
97
9, 11, 17
11, 17
17
2
3
2
4
5
2
2
96
98
17
17
6
7
1.5
2
95
95
9, 11, 17
17
8
2.5
94
11, 17
a
All reactions were carried out in the presence of NaBH
Yields refer to isolated pure products.
4
(0.2 eq) in refluxing Ac
2
O (1 mL).
b
D
ꢀ
the product was determined by comparison of its specific rotation ([a] ¼ þ58.6 in
CHCl , c 3.44) with the reported data for S-(þ)-1,2-diacetoxy-1-phenylethane
3
D
ꢀ
[18]
(
[a] ¼ þ46.5 in CHCl , c 3.44), which is considered to be 73% optically pure.
3
The effect of other hydride transferring agents on this transformation was
examined with direct conversion of styrene and cyclohexene oxides to the corre-
sponding vic-diacetates by 0.2 molar equivalents of LiAlH , CaH , and NaH in
4
2
Scheme 2. Conversion of optically active R-(þ)-styrene oxide to S-(þ)-1,2-diacetoxy-1-phenylethane with
NaBH =Ac O system.
4
2

640
B. ZEYNIZADEH AND L. SADIGHNIA
Table 3. Conversion of styrene and cyclohexene oxides to the corresponding 1,2-diacetates with LiAlH
a
CaH , and NaH
2
4
,
LiAlH
4
CaH
2
NaH
b
b
Time (h) Yield (%) Time (h) Yield (%) Time (h) Yield (%)
b
Entry Epoxide
Product
1
1.7
1.6
95
96
1.8
1.7
96
93
1.8
1.7
94
93
2
a
All reactions were carried out with 0.2 eq hydride reagents in refluxing Ac
Yields refer to isolated pure products.
2
O (1 mL).
b
refluxing acetic anhydride. All reactions were carried out efficiently within 1.6–1.8 h
and showed the same efficiency and catalytic activity as NaBH (Table 3).
4
The merit of this synthetic method was featured by comparison of our results
[12]
[11]
[13]
with those of reported for HY zeolite,
Bu P,
3
and Er(OTf)3
(Table 4). The
current protocol shows high to comparable efficiency relative to other protocols.
Although we never investigated a complete mechanistic pathway on this
transformation, a tentative explanation is depicted in Scheme 3. We think that the
catalytic loop of this mechanism includes these steps: (i) complexation of the epoxide
ring with sodium (Li or Ca) cation produces A species, (ii) the reaction of A with the
generated anion acetate forms alkoxy acetate B, and finally (iii) the reaction of
alkoxy acetate B with acetic anhydride produces 1,2-diacetate C.
In conclusion, we have shown that the catalytic amounts of NaBH promoted
4
direct conversion of structurally different epoxides to the corresponding 1,2-diacetates.
Table 4. Comparison of the effect of catalysts for conversion of epoxides to their 1,2-diacetates
a
Entry
Epoxide
Catalyst
NaBH
HY Zeolite
Amount (mmol)
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
4
0.2
50 mg
0.1
1.5
12
96
90
98
[11]
[
12]
b
Bu
3
P
24
2
[
13]
c
Er(OTf)
NaBH
[11]
HY Zeolite
3
0.001
0.2
0
4
1.5
10
95
85
92
93
94
95
96
––
50 mg
0.1
[
12]
b
Bu
3
P
24
3
[13]
Er(OTf)
NaBH
[11]
HY Zeolite
3
0.001
0.2
4
2.5
10
10
11
12
50 mg
0.1
––
[
12]
b
Bu
3
P
Er(OTf)
24
––
[13]
3
a
b
Amount of catalyst per 1 mmol of epoxide.
Reaction time was not reported, however, 24 h was the reported time for ring openning–acetolysis of
N-tosylaziridines.
c
No reaction occured on aromatic epoxides.

CONVERSION OF EPOXIDES TO 1,2-DIACETATES
641
Scheme 3. Catalytic cycle of conversion of epoxides to 1,2-diacetates with hydride transferring agents in
Ac O.
2
The reactions were carried out efficiently in refluxing Ac O within 1.5–2.5 h. Conver-
2
sion of R-(þ)-styrene oxide to S-(þ)-1,2-diacetoxy-1-phenylethane was carried out in
ꢀ
good yield and stereospecificity with a NaBH =Ac O system at 0 C. LiAlH , CaH ,
4
4
2
2
and NaH with the same efficiency and catalytic activity as NaBH converted styrene
4
and cyclohexene oxides to the corresponding 1,2-diacetates. We believe that in view of
the low cost and easy availability of the reagents, catalytic nature of the protocol, and
the perfect efficiency, this method could be considered a synthetically useful addition
to the present methodologies.
EXPERIMENTAL
All reagents and substrates were purchased from commercial sources with
the best quality and were used without further purification. The products were
1
13
characterized by their H= C NMR and infrared (IR) spectra, which were
recorded on 300-MHz Bruker Avance and Thermo Nicolet Nexus 670 Fourier
transform (FT)–IR spectrometers, respectively. All yields refer to isolated pure
products. Thin-layer chromatography (TLC) was applied for the purity determi-
nation of the substrates, products, and reaction monitoring over silica-gel 60 F254
aluminum sheet.
Typical Procedure for Conversion of Epoxides to 1,2-Diacetates
with NaBH4
In a round-bottomed flask (10 mL) equipped with magnetic stirrer and
condenser, a solution of styrene oxide (0.12 g, 1 mmol) in acetic anhydride (1 mL)
was prepared. NaBH (0.008 g, 0.2 mmol) was then added, and the reaction mixture
4
was stirred for 1.5 h under reflux conditions. After completion of the reaction, an

642
B. ZEYNIZADEH AND L. SADIGHNIA
aqueous solution of NaHCO (5%, 5 mL) was added, and the mixture was stirred for
3
an additional 5 min. The mixture was extracted with Et O (3 ꢂ 8 mL) and then dried
2
over anhydrous sodium sulfate. Evaporation of the solvent and short-column chro-
matography of the resulting crude material over silica gel (n-hexane–EtOAc: 5=2)
afforded liquid 1,2-diacetoxy-1-phenylethane (0.215 g, 96%, Table 2).
Spectra Data of Compounds (1–8)b
1
,2-Diacetoxy-1-phenylethane (1b). H NMR (CDCl3, 300 MHz)
1
.40–7.31 (m, 5H), 6.02 (dd, J 4.2, 7.8 Hz, 1H), 4.39–4.25 (m, 2H), 2.10 (s, 3H),
d
7
2
1
1
1
3
.06 (s, 3H); C NMR (CDCl , 75.5 MHz) d 170.64, 170.05, 136.50, 128.64,
3
ꢃ1
28.63, 126.70, 73.32, 66.09, 21.10, 20.78; IR (nmax=cm , neat) 3034, 2954, 1743,
455, 1435, 1371, 1223, 1047.
1
1
,2-Diacetoxy-3-phenoxypropane (2b). H NMR (CDCl , 300 MHz) d
3
7
1
.32–7.25 (m, 2H), 6.99–6.89 (m, 3H), 5.41–5.34 (m, 1H), 4.43 (dd, J 3.9, 12 Hz,
H), 4.29 (dd, J 6, 12 Hz, 1H), 4.11 (d, J 5.1 Hz, 2H), 2.09 (s, 3H), 2.06 (s, 3H);
1
3
C NMR (CDCl , 75.5 MHz) d 170.57, 170.26, 158.27, 129.53, 121.36, 114.59,
3
ꢃ1
6
1
9.76, 65.96, 62.54, 20.92, 20.70; IR (nmax=cm , neat) 3041, 2957, 1746, 1600,
588, 1497, 1371, 1228, 1050.
1
1
,2-Diacetoxy-3-allyloxypropane (3b). H NMR (CDCl , 300 MHz) d
3
5
5
4
.92–5.76 (m, 1H), 5.27 (dd, J 1.5, 17.4 Hz, 2H), 5.21 (dd, J 3, 17.4, 1H),
.20–5.12 (m, 1H), 4.32 (dd, J 3.9, 12 Hz, 1H), 4.15 (dd, J 6.3, 12 Hz, 1H),
1
.05–3.91 (m, 2H), 3.55 (d, J 5.1 Hz, 2H), 2.07 (s, 3H), 2.03 (s, 3H); C NMR
3
(
2
CDCl , 75.5 MHz) d 170.58, 170.26, 134.13, 117.33, 72.19, 70.21, 68.07, 62.80,
0.94, 20.67; IR (nmax=cm , neat) 2957, 2868, 1743, 1433, 1372, 1225, 1092, 1048.
3
ꢃ1
1
1
,2-Diacetoxy-3-isopropoxypropane (4b). H NMR (CDCl , 300 MHz) d
3
5
3
7
.15–4.96 (m, 1H), 4.28 (dd, J 3.6, 12 Hz, 1H), 4.12 (dd, J 3, 12 Hz, 1H),
1
.58–3.40 (m, 3H), 2.05 (s, 3H), 2.04 (s, 3H), 1.09 (d, J 6 Hz, 6H); C NMR (CDCl3,
3
5.5 MHz) d 170.68, 170.34, 72.32, 70.59, 66.12, 63.00, 21.91, 21.84, 21.00, 20.74; IR
ꢃ1
(
nmax=cm , neat) 2918, 2849, 1743, 1463, 1371, 1229, 1118, 1047.
1
(
2,3-Diacetoxypropyl) Methacrylate (5b). H NMR (CDCl , 300 MHz) d
3
6
.10–6.04 (m, 1H), 5.55–5.54 (m, 1H), 5.30–5.16 (m, 1H), 4.33–4.05 (m, 4H), 2.02
1
3
(s, 3H), 2.00 (s, 3H), 1.87 (s, 3H); C NMR (CDCl , 75.5 MHz) d 170.41, 170.03,
3
ꢃ1
1
2
66.66, 135.65, 126.37, 69.28, 62.39, 62.23, 20.76, 20.57, 18.13; IR (nmax=cm , neat)
988, 2880, 1720, 1638, 1453, 1372, 1320, 1296, 1166, 1077, 1055.
1
1
,2-Diacetoxycyclohexane (6b). H NMR (CDCl , 300 MHz) d 4.79–4.5
3
(
m, 2H), 1.97–1.93 (m, 2H), 1.94 (s, 3H), 1.93 (s, 3H), 1.69–1.62 (m, 2H),
1
3
1
2
1
.36–1.16 (m, 4H); C NMR (CDCl , 75.5 MHz) d 170.37, 170.22, 73.49, 30.16,
3
ꢃ1
9.94, 23.25, 23.11, 21.17, 21.14; IR (nmax=cm , neat) 2942, 2866, 1739, 1452,
368, 1251, 1042.
1
1
,2-Diacetoxy-3-butoxypropane (7b). H NMR (CDCl , 300 MHz) d
3
5
(
1
.20–5.12 (m, 1H), 4.31 (dd, J 3.7, 11.9 Hz, 1H), 4.13 (dd, J 6.3, 12 Hz, 1H), 3.52
d, J 5.4 Hz, 2H), 3.47–3.35 (m, 2H), 2.06 (s, 3H), 2.04 (s, 3H), 1.58–1.45 (m, 2H),
.40–1.26 (m, 2H), 0.88 (t, J 7.3 Hz, 3H); C NMR (CDCl , 75.5 MHz) d 170.73,
3
1
3

CONVERSION OF EPOXIDES TO 1,2-DIACETATES
643
ꢃ1
170.39, 71.43, 70.32, 68.83, 62.98, 31.56, 21.05, 20.78, 19.18, 13.85; IR (nmax=cm
neat) 2959, 2935, 2871, 1743, 1465, 1378, 1238, 1109.
,
1
1
,2-Diacetoxy-3-chloropropane (8b). H NMR (CDCl , 300 MHz) d
3
5
.25–5.13 (m, 1H), 4.37–4.1 (m, 2H), 3.75–3.55 (m, 2H), 2.09 (s, 3H), 2.07 (s, 3H);
C NMR (CDCl , 75.5 MHz) d 170.49, 170.41, 70.39, 62.36, 42.10, 20.86, 20.79;
1
3
3
ꢃ1
IR (nmax=cm , neat) 2963, 1744, 1436, 1371, 1221, 1046.
ACKNOWLEDGMENT
We acknowledge the financial support of this work by the Research Council of
Urmia University.
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