A mild, rapid and highly regioselective ring-opening of epoxides and aziridines with acetic anhydride under solvent-free conditions using ammonium-12-molybdophosphate

Article abstract of DOI:10.1016/j.tetlet.2006.07.055

A highly regioselective ring opening of epoxides and aziridines can be carried out efficiently with acetic anhydride to form the acetates of the corresponding 1,2-diols and 2-amino-alcohols, respectively, using ammonium-12-molybdophosphate (AMP) as a heterogeneous catalyst, at room temperature, in the absence of solvent.

Full text of DOI:10.1016/j.tetlet.2006.07.055

Tetrahedron Letters 47 (2006) 6865–6868
A mild, rapid and highly regioselective ring-opening of epoxides
and aziridines with acetic anhydride under solvent-free
conditions using ammonium-12-molybdophosphateI
Biswanath Das,* V. Saidi Reddy and Fouzia Tehseen
Organic Chemistry Division-1, Indian Institute of Chemical Technology, Hyderabad 50007, India
Received 8 May 2006; revised 6 July 2006; accepted 13 July 2006
Available online 4 August 2006
Abstract—A highly regioselective ring opening of epoxides and aziridines can be carried out efficiently with acetic anhydride to form
the acetates of the corresponding 1,2-diols and 2-amino-alcohols, respectively, using ammonium-12-molybdophosphate (AMP) as a
heterogeneous catalyst, at room temperature, in the absence of solvent.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Epoxides1 and aziridines2 are important precursors
Ac2O
OAc
in organic syntheses. They are capable of reacting with
various nucleophiles to afford 1,2-difunctional products.3
Thus they can be utilized for the preparation of 1,2-diols
and 2-amino-alcohols, which possess valuable synthetic
utilities.4 Earlier, di-O-acetyl-1,2-diols and O-acetyl-2-
amino alcohols were prepared directly from epoxides
and aziridines, respectively, by treatment with Ac2O in
AMP
O
OAc
r.t., 1 h
R
R
Ac2O
NHTs
OAc
AMP
NTs
+
r.t., 1 h
R
the presence of tributylphosphine as
a
catalyst.4
R
OAc
NHTs
R
However, this reaction was conducted under reflux
and reaction times were high (12–48 h). The regioselec-
tivity of the ring opening of 2-phenyl-N-tosyl aziridines
was also not impressive.4 In continuation of our work5
on the development of useful synthetic methodologies,
we now report that ammonium-12-molybdophosphate
(AMP), (NH4)3[PMo12O40]6 can efficiently be applied
for cleavage of epoxides and aziridines with Ac2O to
produce the acetate esters of 1,2-diols and 2-amino-alco-
hols, respectively (Scheme 1).
Scheme 1.
and the products were formed in excellent yields. An
epoxide derived from trisubstituted alkene, such as 1f,
also afforded the desired product, 2f smoothly.5d This
chiral epoxide furnished the product with inversion of
configuration by ring cleavage in an anti manner involv-
ing an SN2 process.3c
The ring opening of epoxides with Ac2O by internal or
external attack of the nucleophile afforded similar prod-
ucts. However, the conversion of aziridines took place
with high regioselectivity. N-Tosyl-2-aryl aziridines
yielded products formed by cleavage at the benzylic po-
sition while N-tosyl-2-alkyl aziridines afforded products
formed by opening at the terminal position. The cleav-
age of symmetrical bicyclic epoxides and N-tosyl aziri-
dines with Ac2O formed trans products. The structures
and stereochemistry of the acetates were established
from their analytical and spectral (1H NMR and MS)
data.
Several epoxides and N-tosyl aziridines underwent ring-
opening easily with Ac2O in the presence of AMP at
room temperature (Table 1). No solvent was required
for the reaction.The conversion was complete in 1 h
Keywords: Epoxide; Aziridine; Acetic anhydride; Ammonium-12-
molybdophosphate; Regioselectivity.
q Part 95 in the series, ‘Studies on novel synthetic methodologies’;
IICT Communication No. 060704.
*
Corresponding author. Tel./fax: +91 40 27160512; e-mail:
biswanathdas@yahoo.com
0040-4039/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.07.055

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B. Das et al. / Tetrahedron Letters 47 (2006) 6865–6868
Table 1. Ring-opening of epoxides and aziridines with acetic anhydride using AMPa
Entry
a
Epoxide/aziridine 1
Product 2
OAc
Isolated yield (%)
O
98
OAc
O
OAc
OAc
O
O
b
96
OAc
O
O
O
OAc
c
94
96
Cl
Cl
OAc
O
O
O
OAc
d
O
Me
MeO
Cl
OAc
O
e
92
Cl
OAc
OAc
O
AcO
O
O
f
91
93
OAc
g
O
OAc
OAc
h
93
O
OAc
OAc
NTs
NHTs
i
j
98
96
OAc
NTs
NHTs
OAc
92b
93b
92b
NTs
k
l
NHTs
OAc
NTs
NHTs
NHTs
NTs
m
OAc
( )
( )
10
10

B. Das et al. / Tetrahedron Letters 47 (2006) 6865–6868
6867
Table 1 (continued)
Entry
Epoxide/aziridine 1
Product 2
NHTs
Isolated yield (%)
94
n
NTs
OAc
NHTs
o
93
NTs
OAc
a The structures of the products were established from their spectral (1H NMR and MS) and analytical data.
b The other regioisomer (ꢀ5%) was also obtained.
In recent years, heteropoly acids and their salts have
gained much importance due to their interesting cata-
lytic activity and ability to carry out reactions in a clean
manner.7 The synthetic utilities of these catalysts has not
yet been fully discovered. The present catalyst, AMP
(the ammonium salt of a heteropoly acid), has been
found to be highly efficient for the ring opening of both
epoxides and aziridines with Ac2O at room temperature.
In the absence of this catalyst, only trace amounts of
products were obtained even after 2 h. The catalyst
operates under heterogeneous conditions and can conve-
niently be handled and separated from the reaction mix-
ture by simple filtration.
(3H, s), 2.03 (3H, s); FABMS: m/z 311 [M+H]+Å. Anal.
Calcd for C16H22O6: C, 61.94; H, 7.10. Found: C, 61.83;
H, 7.17.
Compound 2h: 1H NMR (CDCl3, 200 MHz): d 4.38
(2H, dd, J = 7.3, 2.9 Hz), 2.02 (6H, s), 1.39–1.34 (2H,
m), 1.22–1.14 (6H, m); FABMS: m/z 201 [M+H]+Å.
Anal. Calcd for C10H16O4: C, 60.00; H, 8.00. Found:
C, 60.24; H, 8.17.
Compound 2j: 1H NMR (CDCl3, 200 MHz): d 7.72 (2H,
d, J = 8.0 Hz), 7.28 (2H, d, J = 8.0 Hz), 7.20–7.03 (4H,
m), 5.65 (1H, t, J = 6.0 Hz), 5.32 (1H, t, J = 6.0 Hz),
3.27 (2H, t, J = 6.0 Hz), 2.47 (3H, s), 2.32 (3H, s), 2.01
(3H, s); FABMS: m/z 348 [M+H]+Å. Anal. Calcd for
C18H21NO4S: C, 62.25; H, 6.05; N, 4.03. Found: C,
62.38; H, 6.12; N, 4.11.
In conclusion, we have developed a mild and efficient
method for the preparation of acetate esters of 1,2-diols
and 2-amino-alcohols by ring opening of epoxides and
aziridines, respectively, with Ac2O using AMP as a het-
erogeneous catalyst. The high yields, short reaction
times and excellent regio- and stereoselectivities are
advantages of the present protocol.
Compound 2k: 1H NMR (CDCl3, 200 MHz): d 7.75
(2H, d, J = 8.0 Hz), 7.30 (2H, d, J = 8.0 Hz), 5.11
(1H, d, J = 6.0 Hz), 4.28–4.20 (2H, m), 3.22 (1H, m),
2.41 (3H, m), 1.96 (3H, s), 1.59–1.42 (2H, m),
1.31–1.11 (4H, m), 0.82 (3H, t, J = 8.0 Hz); FABMS:
m/z 314 [M+H]+Å. Anal. Calcd for C15H23NO4S: C,
57.51; H, 7.35; N, 4.47. Found: C, 57.65; H, 7.42; N,
4.52.
General experimental procedure: To a mixture of epoxide
(or N-tosyl aziridine) (1 mmol) and Ac2O (1.2 mmol),
AMP (10 mol %) was added. The mixture was stirred
at room temperature for 1 h. TLC indicated the comple-
tion of the reaction. Water–EtOAc (1:1) (10 ml) was
added and the mixture was shaken and filtered. The
organic portion was separated from the filtrate and the
aqueous portion was extracted twice with EtOAc
(2 · 5 ml). The combined organic portions were concen-
trated and subjected to column chromatography (silica
gel, hexane–EtOAc) to afford the ester.
Compound 2o: 1H NMR (CDCl3, 200 MHz): d 7.76
(2H, d, J = 8.0 Hz), 7.28 (2H, d, J = 8.0 Hz), 5.79
(1H, d, J = 6.8 Hz), 4.83 (1H, ddd, J = 9.0, 7.6,
4.0 Hz), 3.42 (1H, m), 2.41 (3H, s), 2.10–1.88
(2H, m), 1.85 (3H, s), 1.72–1.38 (6H, m); FABMS:
m/z 312 [M+H]+.. Anal. Calcd for C15H21NO4S: C,
57.88; H, 6.75; N, 4.50. Found: C, 57.96; H, 6.82; N,
4.58.
The spectral and analytical data of some representative
acetates are given below:
1
Acknowledgement
Compound 2a: H NMR (CDCl3, 200 MHz): d 7.42–
7.28 (5H, m), 6.01 (1H, dd, J = 7.8, 4.3 Hz), 4.33 (1H,
dd, J = 12.0, 4.3 Hz), 4.21 (1H, dd, J = 12.0, 7.8 Hz),
2.02 (3H, s), 2.05 (3H, s); FABMS: m/z 223 [M+H]+Å.
Anal. Calcd for C12H14O4: C, 64.86; H, 6.31. Found:
C, 64.72; H, 6.38.
The authors thank CSIR and UGC, New Delhi, for
financial assistance.
References and notes
Compound 2d: 1H NMR (CDCl3, 200 MHz): d 7.08
(2H, d, J = 8.0 Hz) 6.79 (2H, d, J = 8.0 Hz), 5.30 (1H,
m), 4.41 (1H, dd, J = 12.0, 3.8 Hz), 4.25 (1H, dd,
J = 12.0, 6.0 Hz), 4.06 (2H, d, J = 5.3 Hz), 3.51 (2H, t,
J = 7.0 Hz), 3.30 (3H, s), 2.76 (2H, t, J = 7.0 Hz), 2.08
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