A novel method for the synthesis of α,β-unsaturated amides mediated by Samarium diiodide

Article abstract of DOI:10.1002/jccs.200500133

Promoted by Samarium diiodide (SmI₂), α,β-unsaturated amides were formed from nitrogenanions (formed in situ by the reduction of nitro compounds) and αβ-unsaturated esters. This reaction contrasts with the conjugate addition between amines and α,β-unsaturated esters promoted by samarium triiodide (SmI₃) and provides an alternative attractive way to obtain α,β-unsaturated amides using SmI ₂.

Full text of DOI:10.1002/jccs.200500133

Journal of the Chinese Chemical Society, 2005, 52, 953-955
953
A Novel Method for the Synthesis of a,b-Unsaturated Amides Mediated by
Samarium Diiodide
Chun-Lan Zhu (
College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua,
) and Xia-Xia Wang* (
)
Zhejiang, 321004, P. R. China
Promoted by Samarium diiodide (SmI2), a,b-unsaturated amides were formed from nitrogen anions
(formed in situ by the reduction of nitro compounds) and a,b-unsaturated esters. This reaction contrasts with
the conjugate addition between amines and a,b-unsaturated esters promoted by samarium triiodide (SmI3)
and provides an alternative attractive way to obtain a,b-unsaturated amides using SmI2.
Keywords: Samarium diiodide (SmI2); Nitro compounds; a,b-Unsaturated esters; a,b-Unsaturated
amides.
Scheme I
INTRODUCTION
Recently, Concellón et al.1 reported a stereoselective
R3
R1
R3
X
R1
NHR
R2
b-elimination of 2-chloro-3-hydroxyamides using samarium
diiodide (SmI2) to synthesize a,b-unsaturated amides. Here-
in we wish to describe an alternative way employing SmI2 to
prepare a,b-unsaturated amides from nitro compounds and
a,b-unsaturated esters.
2
SmI2 / THF
R
NO2
R N(SmI2)2
R2
O
r. t.
1
3
X = -COOR, -CN, -CON(CH3)2
Nitro compounds could be reduced by samarium diio-
dide (SmI2) to give the corresponding amines easily in the
presence of a proton source such as MeOH.2 Amines, as were
reported, could undergo conjugate addition with a,b-unsatu-
rated esters (nitriles) promoted by samarium triiodide (SmI3)
to yield the corresponding b-amino esters and b-amino ni-
triles in satisfactory yields.3 However, in the absence of a pro-
ton source (with dry THF as the solvent), nitro compounds
could be reduced by SmI2 to form a nitrogen anion,4a which
was a living species, and may have a different reactivity com-
pared with its parent amine. Ooi and Tayama et al. reported
that dilithium amides resulting from aromatic amines and
BuLi when treated with esters could afford a convenient and
efficient preparation of aromatic sec-amides.4b Herein we
wish to report our study on the reaction between the nitrogen
anions (formed in situ by the reduction of nitro compounds
with SmI2 in THF) and a,b-unsaturated compounds, includ-
ing a,b-unsaturated esters, a,b-unsaturated nitrile and a,b-
unsaturated amide (Scheme I).
RESULTS AND DISCUSSION
The results are summarized in Table 1. Nitrogen anions
resulting from the reduction of nitro compounds by SmI2/
THF could substitute the alkoxy group in the a,b-unsaturated
esters and give the corresponding a,b-unsaturated amides in
good yields; the conjugation addition products not isolated
(Entries 1-7, Table 1). While acrylonitrile and N,N-dimethyl
acrylamides when used as the substrates failed to afford en-
couraging results.
It can be concluded that the nitrogen anions undergo
aminolysis with the ester groups readily, while they show less
tendency to attack the electron-deficient C=C bonds than
their parent amines.3 The nitrogen anion thus formed did not
attack the CºN smoothly (entry 8, Table 1), neither did it un-
dergo amino exchange reactions to afford a new a,b-unsatu-
rated amides in reasonable yield (entry 9, Table 1).
To summarize, an alternative way for the synthesis of
* Corresponding author. E-mail: wangxxzj@163.com

954 J. Chin. Chem. Soc., Vol. 52, No. 5, 2005
Zhu and Wang
Table 1. Formation of a,b-unsaturated amides from nitro compounds and a,b-unsaturated
compounds mediated by SmI2
Entry
R
R1
R2
R3
X
Product Yield (%)a
1
2
3
4
5
6
7
8
9
C6H5
H
H
H
H
H
H
Ph
H
H
H
H
H
H
H
H
H
H
H
CH3
H
H
CH3
H
H
H
H
H
COOCH3
COOC2H5
COOC2H5
COOCH3
COOC2H5
COOC2H5
COOC2H5
CN
3a
3b
3c
3d
3e
3f
3g
3h
3i
70
76
82
73
71
68
78
2-CH3C6H4
4-CH3C6H4
4-CH3C6H4
4-ClC6H4
2-Naphthyl
CH3
b
C6H5
4-CH3C6H4
-
c
CON(CH3)2
-
a Isolated yields based on compound 1. b A very complex mixture was obtained and no efforts
were made for the isolation and characterization. c 80% of p-Tolylamine was obtained.
a,b-unsaturated amides using SmI2 was reported. With readily
available starting materials (nitro compounds and a,b-unsat-
urated esters) and mild reaction conditions (neutral, at room
temperature), the method may make a novel and useful addi-
tion to the previous methods5 for the preparation of a,b-un-
saturated amides.
gave a residue, which was purified by preparative TLC on sil-
ica gel using ethyl acetate-cyclohexane (1:4) as eluent.
2-Methyl-N-phenyl-acrylamide 3a
White solid; mp 85-87 °C (lit.6 85-85.5 °C). IR nmax
1
(KBr) 3294, 3127, 3056, 2984, 1658, 1621, 1594; H NMR
(CDCl3): d 7.50 (d, 2H, J = 8.0), 7.48 (s, br, 1H), 7.31-7.36
(m, 2H), 7.11-7.14 (m, 1H), 5.79 (s, 1H), 5.47 (s, 1H), 2.02 (s,
3H).
EXPERIMENTAL SECTION
THF was distilled from sodium-benzophenone imme-
diately prior to use. All reactions were conducted under a ni-
trogen atmosphere. Melting points are uncorrected. 1H NMR
spectra were recorded on a Bruker 400 MHz instrument as
CDCl3 solutions using TMS as internal standard. Chemical
shifts (d) are reported in ppm and coupling constants J are
given in Hz. IR spectra were recorded using KBr disks with a
Bruker Vector-22 infrared spectrometer.
N-o-Tolyl-acrylamide 3b
White solid; mp 112-114 °C (lit.7 113-114 °C). IR nmax
1
(KBr) 3219, 3112, 3026, 2921, 2852, 1655, 1627, 1604; H
NMR (CDCl3): d 7.92 (s, 1H), 7.05-7.25 (m, 4H), 6.30-6.46
(m, 2H), 5.78 (d, 1H, J = 10.0 Hz), 2.28 (s, 3H).
N-p-Tolyl-acrylamide 3c
White solid; mp 139-141 °C (lit.6 141-142 °C). IR nmax
(KBr) 3287, 3132, 3080, 2920, 2853, 1664, 1637, 1608,
1546; 1H NMR (CDCl3): d 7.46 (d, 2H, J = 8.0 Hz), 7.20 (s,
1H, br), 7.14 (d, 2H, J = 8.0 Hz), 6.20-6.45 (m, 2H), 5.75 (d,
1H, J = 10.0 Hz), 2.32 (s, 3H).
General procedure for the synthesis of a,b-unsaturated
amides (3a-3g)
The nitro compound (1 mmol) in 2 mL of dry THF was
added first by syringe to the solution of 6 mmol SmI2 in dry
THF (30 mL) at room temperature under nitrogen atmo-
sphere. After the disappearance of the characteristic blue
color of samarium diiodide (within 10 minutes), the a,b-un-
saturated esters (1.1 mmol) in 2 mL of dry THF was then
added to realize the N-acylation. After completion of the re-
action (about 1 hour, monitored by TLC), 0.1 N of hydrochlo-
ride acid (3 mL) was added and the mixture was extracted
with ether (3 ´ 20 mL). The combined extracts were washed
with saturated brine (15 mL) and dried over anhydrous so-
dium sulfate. Removal of the solvent under reduced pressure
2-Methyl-N-p-tolyl-acrylamide 3d
White solid; mp 85-87 °C (lit.6 88-88.5 °C). IR nmax
1
(KBr) 3269, 3110, 3032, 2921, 1656, 1623, 1595; H NMR
(CDCl3): d 7.44-7.47 (m, 3H), 7.14 (d, 2H, J = 8.0 Hz), 5.77
(s, 1H), 5.44 (s, 1H), 2.32 (s, 3H), 2.06 (s, 3H).
N-(4-Chloro-phenyl)-acrylamide 3e
White solid; mp 185-187 °C (lit.8 187 °C). IR nmax
(KBr) 3276, 3199, 3128, 3079, 1665, 1628, 1608, 1551; 1H
NMR (DMSO): d 10.26 (s, 1H), 7.67-7.69 (d, 2H, J = 8.8 Hz),

The Synthesis of a,b-Unsaturated Amides by SmI2
J. Chin. Chem. Soc., Vol. 52, No. 5, 2005 955
7.36-7.38 (d, 2H, J = 8.8 Hz), 6.40 (dd, 1H, J = 10, 17 Hz),
6.23-6.28 (m, 1H), 5.76 (dd, 1H, J = 10, 1.8 Hz).
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N-Naphthalen-1-yl-acrylamide 3f
Light purple solid; mp 142-143 °C (lit.7 144 °C). IR
nmax (KBr) 3265, 3031, 1658, 1626, 1546; 1H NMR (CDCl3):
d 7.44-8.01 (m, 8H), 6.44-6.53 (m, 2H), 5.81-5.85 (m, 1H).
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White solid; mp 110-112 °C (lit.9 111.8-112.4 °C). IR
1
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ACKNOWLEDGEMENT
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We are grateful to the Education Foundation of Zhejiang
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Received August 2, 2004.