An efficient synthesis of conjugated nitro-olefins using ceric ammonium nitrate

Article abstract of DOI:10.1016/j.tetlet.2005.09.126

An efficient method for the synthesis of conjugated nitro-olefins from α,β-unsaturated acids under extremely mild conditions using ceric ammonium nitrate (CAN) at room temperature in acetonitrile in moderate to good yields is described.

Full text of DOI:10.1016/j.tetlet.2005.09.126

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 8141–8143
An efficient synthesis of conjugated nitro-olefins using
ceric ammonium nitrate
A. Sridhar Rao, P. V. Srinivas, K. Suresh Babu and J. Madhusudana Rao*
Natural Products Laboratory, Organic Chemistry Division-I, Indian Institute of Chemical Technology, Hyderabad 500 007, India
Received 5 July 2005; revised 14 September 2005; accepted 21 September 2005
Available online 7 October 2005
Abstract—An efficient method for the synthesis of conjugated nitro-olefins from a,b-unsaturated acids under extremely mild
conditions using ceric ammonium nitrate (CAN) at room temperature in acetonitrile in moderate to good yields is described.
Ó 2005 Elsevier Ltd. All rights reserved.
1. Introduction
CH=CH-COOH
CAN, CH CN
CH=CH-NO2
3
The nitro group is a powerful electron-withdrawing sub-
stituent and this property dominates the chemistry of all
molecules containing this functional group. Nitroalk-
enes are powerful dienophiles in the Diels–Alder reac-
1
-3 h, r.t
R
R
Scheme 1.
1
tion. The versatility of the nitro group makes possible
its transformations into many compounds with diverse
functionalities. Removal of a nitro group leading to
the formation of carbonyl compounds in the classical
ucts using N O as the nitrating agent in the presence of
2 4
CAN, however, the reaction was handicapped by low
yields. To further explore the usage, herein, we report
a novel method for the synthesis of nitro-alkenes from
a,b-unsaturated aromatic acids using CAN in aceto-
nitrile at room temperature (Scheme 1).
1
Nef reaction is well known. Significant biological activi-
2
ties have been reported for some nitro-olefins.
Several methods are reported in the literature for the
synthesis of nitro-olefins. All these center on the classical
Henry reaction, involving the condensation of alde-
hydes/ketones with nitroalkanes and subsequent dehy-
dration of the b-nitro alcohols. A variety of reagents
In a typical experimental procedure, a mixture of CAN
and ferulic acid (entry 2) in acetonitrile was stirred for
2 h at room temperature and the product was obtained
in 80% yield. In a similar fashion, various nitro-olefins
were synthesized and their isolated yields are tabulated
in Table 1. Substitution on the phenyl ring, especially
with electron-donating groups, improved the yields.
3
have been used for dehydration such as phthalic anhy-
4
5
dride,
dicyclohexylcarbodiimide,
methanesulfonyl
6
7
chloride, pivaloyl chloride, etc.
Synthesis of nitro-alkenes has also been achieved by
direct condensation of aldehydes/ketones with nitroalk-
anes using heterogeneous catalysts such as Envirocat
The present letter deals with the formation of the ipso-
substituted product exclusively, in moderate to good
yields at ambient temperatures. We suggest that the
change in reaction solvent to acetonitrile is responsible
for the exclusive formation of the ipso-product, without
the formation of the ring-substituted product.
8
9
EPZG and GEBC.
Ceric ammonium nitrate (CAN) has been employed as a
1
0–12
mild oxidizing agent in organic synthesis.
Peterson
1
0
et al. reported the formation of ring-substituted prod-
2. General experimental procedure
Keywords: Ceric ammonium nitrate; Acetonitrile; Cinnamic acids;
b-Nitrostyrene.
Acid (0.515 mmol) and CAN (1 mmol, 2 equiv) were
stirred in acetonitrile (10 ml) at room temperature
for 1h. The reaction was monitored by TLC. After
*
Corresponding author. Tel.: +91 040 27193166; fax: +91 040
7160512; e-mail: janaswamy@iict.res.in
2
0040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.09.126

8142
A. Sridhar Rao et al. / Tetrahedron Letters 46 (2005) 8141–8143
Table 1. Conversion of a,b-unsaturated acids in to conjugated nitro-olefins
S. No.
1
Substrate
Product
HO
Time (h)
175
Yields (%)
O
NO2
HO
OH
HO
HO
O
MeO
HO
NO2
MeO
HO
2
3
OH
OH
2
80
70
O
MeO
MeO
NO2
NO2
MeO
MeO
1.5
O
MeO
AcO
MeO
AcO
OH
4
5
6
3
60
65
70
O
O
MeO
BnO
NO2
NO2
MeO
Bno
OH
OH
3
2.5
MeO
O
MeO
O
OH
7
8
1.5
5
75
40
NO2
NO2
O
O
OH
Cl
Cl
O
NO2
9
5
40
75
OH
O
MeO
MeO
NO2
MeO
MeO
OH
10
1.5
OMe
OMe
OMe
O
OMe
NO2
OMe
1
1
1
2
OH
1.5
5
75
30
OMe
O
NO2
OH
O N
O N
2
2
completion of the reaction, the acetonitrile was removed
under vacuum and the residue dissolved in EtOAc, the
solution washed with water then dried over anhydrous
Na SO . The crude product was subjected to column
(100). Anal. Calcd for C H NO : C, 57.41; H, 5.26.
10 11 4
Found: C, 57.38: H, 5.24.
2.2. 3-Methoxy-4-acetoxy-b-nitrostyrene
2
4
chromatography over silica gel and eluted with 20%
EtOAc in hexane to obtain the pure compound. All
the products were characterized by IR, H NMR, and
mass spectroscopic methods and also by comparison
with the reported values.
1
H NMR (CDCl , 200 MHz): 2.36 (s, 3H, COCH ), 3.96
3
3
1
(s, 3H, OMe), 7.12–7.18 (m, 3H), 7.54 (d, 1H, J = 12 Hz,
olefinic), 7.98 (d, 1H, J = 12 Hz, olefinic). Mass: m/z:
237 (100).
2
.1. 2,6-Dimethoxy-b-nitrostyrene
2.3. 3-Methoxy-4-benzyloxy-b-nitrostyrene
1
1
H NMR (CDCl , 200 MHz): 3.82 (s, 3H, OMe), 3.98 (s,
H NMR (CDCl , 200 MHz): 3.80 (s, 3H, OMe), 5.20
3
3
3
H, OMe), 6.92–7.10 (m, 3H), 7.90 (d, 1H, J = 12 Hz,
(s, 2H, OCH ), 6.30 (d, 1H, J = 12 Hz, olefinic), 6.99
2
1
3
olefinic), 8.18 (d, 1H, J = 12 Hz, olefinic). C NMR
CDCl , 75 MHz): 55.8, 56.0, 112.4, 116.3, 119.1,
(s, 1H), 7.40–7.60 (m, 6H), 7.70 (d, 1H), 8.20 (d, 1H,
1
3
(
J = 12 Hz, olefinic);
C NMR (CDCl , 75 MHz):
3
3
1
19.1, 135.1, 138.6, 153.6, and 153.9. Mass: m/z: 209
153.6, 150.5, 139.8, 136.5, 131.5, 129.2, 128.5,

A. Sridhar Rao et al. / Tetrahedron Letters 46 (2005) 8141–8143
8143
1
27.2, 124.3, 114.5, 111.5, 71.0, 56.5. Mass: m/z: 285
McGowan, J. C. Nature 1946, 158, 876–877; (c) McGowan,
J. C.; Brian, P. W.; Hemming, H. G. Ann. Appl. Biol. 1948,
(
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In conclusion, we have developed a simple, novel, effi-
cient and mild methodology for the conversion of aryl
a,b-unsaturated acids into conjugated nitro-olefins using
ceric ammonium nitrate at room temperature. It is antici-
pated that this method will find wide applications in the
synthesis of bioactive nitro-alkenes.
3
3
5, 3219–3222.
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Acknowledgements
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The authors thank Dr. J. S. Yadav Director IICT, for
his constant support and encouragement. K.S.B. thanks
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