Microwave-assisted one-pot synthesis of α, β-unsaturated amides under solvent-free conditions

Article abstract of DOI:10.3184/030823409X393682

Under microwave-assisted solvent-free conditions a one-pot reaction of triphenylphosphine, an aldehyde and N, N-diethyl chloroacetamide in the presence of zinc dust affords α, β-unsaturated amides stereoselectively in good yield. In comparison with the co

Full text of DOI:10.3184/030823409X393682

24 RESEARCH PAPER
JANUARY, 24–26
JOURNAL OF CHEMICAL RESEARCH 2009
Microwave-assisted one-pot synthesis of Į, ȕ-unsaturated amides under
solvent-free conditions
Shilei Jianga, Yuanyuan Xieb and Xiaochun Yua*
aCollege of Chemistry and Materials Engineering, Wenzhou University, Wenzhou, 325027, P.R. China
b
College of Pharmaceutical Sciences, Zhejiang University of Technology, Hangzhou 310014, P.R. China
Under microwave-assisted solvent-free conditions a one-pot reaction of triphenylphosphine, an aldehyde and
N, N-diethyl chloroacetamide in the presence of zinc dust affords D, E-unsaturated amides stereoselectively in good
yield. In comparison with the conventional heating method, the reaction was finished within five minutes under
microwave irradiation.
Keywords: microwave irradiation, solvent-free conditions, D, E-unsaturated amides
Two pioneering papers1-2 appeared in 1986 on the remarkable
CONEt2
H
H
Zn
Ph P
MW
/
acceleration of many organic reactions upon irradiation
with microwaves. Since then microwave-assisted organic
synthesis has become increasingly popular in conventional
and combinatorial synthesis, such as the Wittig reaction,3,4
and the Suzuki reaction.5 D,E-Unsaturated amides have
been used as building blocks in organic synthesis6-8 to
prepare natural products.9 Moreover, D, E-unsaturated
amides show both biological and insecticide activity. Several
methods for their synthesis have appeared, involving Rh-
catalysed aminocarbonylation of alkynes,10 Pt-catalysed
aminocarbonylation of iodoalkenes or iodobenzene,11-16 SmI2
promoted elimination of D,E-epoxyamides17 or 2-chloro-3-
hydroxyamides,18 the reaction of dichloroamide and aldehydes
promoted by Rieke manganese,19 Horner–Wadsworth–
Emmons reaction,20 Peterson reaction,21 zinc-promoted
reaction of bromoacetamide.22 However, most reactions need
a long time and the metallic reagents can be expensive or are
GLI¿FXOWꢀ WRꢀ KDQGOHꢁ23 Thus, there is a need to accelerate the
reaction and to use inexpensive metallic reagents.
3
ClCH2CONEt2
+
PhCHO
Ph
Scheme 1
Table
1 Results of different powers and temperatures
with triphenylphosphine, N, N-diethyl chloroacetamide and
benzaldehyde
Entry
Power/W
Temperature/°C
Time/min
Yielda/%
1
2
3
4
5
6
7
8
9
10
500
700
100
100
100
100
100
120
130
150
160
150
5
5
46
53
58
65
69
72
76
85
86
86
800
5
900
5
1000
1000
1000
1000
1000
1000
5
5
5
5
5
10
Our research group has been interested in the synthesis
of D,E-unsaturated amides, and we have reported the
synthesis of D,E-unsaturated amides by the Wittig reaction of
phosphonium ylids. We report here the microwave-assisted
one-pot reaction of D,E-unsaturated amides promoted by zinc
under solvent-free conditions.
Initially we aimed to use the classical Reformastky-type
condensation of N, N-diethylchloroacetamide and aldehyde
promoted by zinc dust to obtian D,E-unsaturated amides.
However, no product was formed in the reaction. The reaction
occurred when triphenylphosphine was added. The reaction
of triphenylphosphine, N, N-diethyl chloroacetamide,
benzaldehyde was studied as the model reaction (Scheme 1)
to explore different conditions.
We investigated the effect of different power and
temperature of the microwave on the one-pot reaction. The
results were summarised in Table 1.
As Table 1 shows, the yield improved with higher power and
1000W was the optimum 150°C was the optimal temperature.
There was no obvious change with higher temperatures. We
also lengthened the reaction time from 5 to 10 min but no
obvious change was apparent.
To test the generality of the reaction, several aldehydes were
treated with triphenylphosphine, N,N-diethyl chloroacetamide
and zinc under the optimised conditions (Scheme 2). The
results are listed in Table 2.
In these experiments, it was found that the use of zinc dust
increased the yield. In these experiments, it was found that
not only aromatic aldehydes and aliphatic aldehydes but also
heterocyclic aldehydes and the aldehyde with the double
aIsolated yield.
CONEt2
H
Zn
Ph P
MW
/
3
ClCH2CONEt2
+
RCHO
R
H
3
1
2
Scheme 2
bond conjugated with the carbonyl group reacted smoothly
under the same conditions. By comparison acetophenone was
unreactive with the traditional thermal method, the reaction
time was shortened from 16 h to 5 min under microwave
irradiation.
1
The ratios of Z/E isomers were determined by H NMR.
By comparison with the literature data which reported the
selective synthesis of the (E)-D, E-unsaturated amides, we
found the chemical shifts of the vinyl and the ethyl protons
of the (E)-isomer corresponded with that of major product of
the reaction.
The possible mechanism of the reaction was
investigated. When zinc powder, an aldehyde and N, N-
diethylamidemethylenetriphenylphosphoniumsaltwhichcould
be synthesised easily by the reaction of triphenylphosphine
and N, N-diethylchloroacetamide were added together under
microwave irradiation, the D, E-unsaturated amide and
triphenylphosphine oxide were obtained. We also used GCMS
to follow the reaction, and observed the formation of N, N-
diethylamidemethylene triphenylphosphorane ylid. It was
noteworthy that the ylid was not found by GCMS when we
added only the phosphonium salt and zinc powder together.
* Correspondent. E-mail: xiaochunyu@wzu.edu.cn

JOURNAL OF CHEMICAL RESEARCH 2009 25
MHz, CDCl3/TMS): G 1.22 (m, 6 H), 3.48 (m, 4 H), 6.79 (d, 1 H,
J = 15.4 Hz), 7.33 (d, 2 H, J = 7.4 Hz), 7.43 (d, 2 H, J = 7.5 Hz),
7.64 (d, 1 H, J = 15.4 Hz) ppm. 13C NMR (75 MHz, CDCl3/TMS):
G = 13.13, 15.04, 118.31, 128.87, 129.74, 133.91, 135.12, 140.80,
165.33. Elemental Anal. Calcd for C13H16ClNO: C, 65.68; H, 6.78;
N, 5.89. Found: C, 65.84; H, 6.86, N, 6.02%. MS: m/z (%) 237 (M+,
27), 222 (12) 165 (99), 137 (22), 102 (25), 75 (10), 44 (18).
Table 2 Synthesis of D,E-unsaturated amides
Entry
R
Product
Yielda/%
Z/Eb
1
2
3
4
5
6
7
8
4-NO2C6H4
4-ClC6H4
3a
3b
3c
3d
3e
3f
93
83
78
86
75
89
79
85
10:90
9:91
12:88
15:85
11:89
7:93
4-BrC6H4
4-CF3C6H4
4-CH3C6H4
2-NO2C6H4
2-CH3OC6H4
N,N-diethyl-3-(4-bromophenyl)acrylamide (3c): Oil; Z/E = 12:88.
IR(KBr)(cm-1):2975,1648,1605,1489,975,813.1HNMR(300MHz,
CDCl3/TMS): G 1.22 (m, 6 H), 3.45 (m, 4 H), 6.80 (d, 1 H, J = 15.4
Hz), 7.28 (d, 2 H, J = 8.9 Hz), 7.46 (d, 2 H, J = 8.3 Hz), 7.62 (d, 1
H, J = 15.4 Hz) ppm. 13C NMR (75 MHz, CDCl3/TMS): G = 13.16,
15.08, 41.11, 42.29, 118.43, 123.48, 130.04, 131.94, 134.40, 140.96,
165.38. MS: m/z (%) 282 (M+, 19), 209 (99), 181 (18), 126 (32), 102
(92), 77 (14), 58 (22).
3g
3h
13:87
11:89
C6H5
O
9
3i
3j
82
84
7:93
O
10
10:90
O
1ꢀ1ꢁGLHWK\OꢁꢂꢁꢃꢄꢁꢃWULÀXRURPHWK\OꢅSKHQ\OꢅDFU\ODPLGHꢆ (3d): Oil;
Z/E = 15:85. IR (KBr) (cm-1): 2975, 1648, 1606, 975, 813. 1H NMR
(300 MHz, CDCl3/TMS): G 1.23 (m, 6 H), 3.48 (m, 4 H), 6.89 (d,
11
12
13
14
C6H5CH=CH
C6H5CH2CH2
C3H7
3k
3l
72
70
12:88
9:91
11:89
–
3m
58
1 H, J = 15.4 Hz), 7.65 (m, 4 H), 7.70 (d, 1 H, J = 15.4 Hz) ppm. 13
C
PhCOCH3
3n
Trace
NMR (75 MHz, CDCl3/TMS): G = 13.06, 15.01, 41.11, 42.30, 120.32,
125.64, 127.81, 128.64, 138.88, 140.44, 165.06. MS: m/z (%) 271
(M+, 48), 256 (26), 199 (100), 151 (82), 126 (43), 102 (20), 72 (34),
58 (54).
aIsolated yield, product characterised by 1H NMR, 13C NMR, IR, MS.
bRatio was determined by 1H NMR (300 MHz, CDCl3) analysis.
N,N-diethyl-3-p-tolylacrylamide (3e): Oil; Z/E = 11:89. IR (KBr)
(cm-1): 2975, 1647, 1605, 979, 813. 1H NMR (300 MHz, CDCl3/
TMS): G 1.21 (m, 6 H), 2.32 (s, 3 H), 3.46 (m, 4 H), 6.77 (d, 1 H,
J = 15.4 Hz), 7.15 (d, 2 H, J = 7.4 Hz), 7.40 (d, 2 H, J = 7.7 Hz),
7.67 (d, 1 H, J = 15.4 Hz) ppm. 13C NMR (75 MHz, CDCl3/TMS):
G = 13.21, 15.04, 21.36, 41.07, 42.28, 116.65, 127.71, 129.45, 132.71,
139.65, 142.30, 165.91. MS: m/z (%) 217 (M+, 32), 202 (10), 145
(100), 115 (28), 91 (12), 72 (6). Elemental Anal. Calcd for C14H19NO:
C, 77.38; H, 8.81; N, 6.45. Found: C, 77.50; H, 8.71; N, 6.71%.
N,N-diethyl-3-(2-nitrophenyl)acrylamide (3f): Oil; Z/E = 7:93. IR
(KBr) (cm-1): 2976, 1647, 1609, 1524, 968, 751. 1H NMR (300 MHz,
CDCl3/TMS): G 1.25 (m, 6 H), 3.48 (m, 4 H), 6.69 (d, 1 H, J = 15.3 Hz),
7.50 (m,1 H), 7.64 (m, 2 H), 8.02 (m, 2 H) ppm. 13C NMR (75 MHz,
CDCl3/TMS): G = 13.06, 14.97, 40.94, 42.37, 123.41, 124.66, 128.53,
129.22, 129.52, 131.94, 133.29, 137.10, 148.24, 164.78. MS: m/z (%)
202 (69), 176 (45), 130 (100), 102 (27), 72 (38), 58 (10).
Thus, we think that it is possibe that the triphenylphosphonium
VDOWꢀ ZDVꢀ IRUPHGꢀ ¿UVWꢂꢀ DQGꢀ WKHQꢀ WKHꢀ FRUUHVSRQGLQJꢀ \OLGꢀ ZDVꢀ
formed in the presence of zinc powder, and the resulted
ylid reacted with the aldehyde immediately to afford the D,
E-unsaturated amides. At the same time, the reaction of ylid
and aldehyde further promoted the formation of the product.
In conclusion, we have demonstrated a very simple
DQGꢀ HI¿FLHQWꢀ VWHUHRVHOHFWLYHꢀ PHWKRGꢀ IRUꢀ PDNLQJꢀ D,
E-unsaturated amides by the microwave-assisted one-pot
reaction of triphenylphosphine, aldehyde and N, N-diethyl
chloroacetamide in the presence of zinc dust under solvent-
free conditions. The reaction does not require the use of
any volatile organic solvents as well as expensive metallic
reagents. Thus, this is an economical and environmentally
friendly method for the synthesis of D, E-unsaturated amides,
DQGꢀ WKHꢀ XVHꢀ RIꢀ WKHꢀ PLFURZDYHVꢀ VLJQL¿FDQWO\ꢀ VKRUWHQHGꢀ WKHꢀ
reaction time.
N,N-diethyl-3-(2-methoxyphenyl)acrylamide(3g):Oil;Z/E=13:87.
IR(KBr)(cm-1):2973,1644,1604,1495,984,754.1HNMR(300MHz,
CDCl3/TMS): G 1.22 (m, 6 H), 3.50 (m, 4 H), 3.89 (s, 3 H), 6.95
(m, 3 H), 7.33 (m, 1 H), 7.50 (d, 1 H, J = 9 Hz), 7.97 (d, 1 H,
J = 15.5 Hz) ppm. 13C NMR (75 MHz, CDCl3/TMS): G = 13.23,
15.04, 41.05, 42.24, 55.30, 114.02, 118.90, 120.91, 125,74, 136.27,
144.23, 160.65, 164.89. MS: m/z (%) 233 (M+, 8), 202 (100), 161
(82), 146 (9), 118 (12), 105 (13), 77 (10).
Experimental
All reactions were conducted in an XH-100A microwave synthesis/
extraction instrument which was made by Beijing Xiang Hu Science
and Technology Development Co. Ltd. Melting points were recorded
on Digital Melting Point Apparatus WRS-1B and uncorrected. TLC
was performed using precoated silica gel 60 GF254 (0.25 mm) and
column chromatography was performed using silica gel (300–400
mesh).1H NMR and 13C NMR spectra were reported on a FT-Bruker
AT-300 instrument using CDCl3 as a solvent with tetramethylsilane
(TMS) as the internal standard J-values are given in Hz. IR spectra
were measured on a Bruker Vector55 instrument. MS were measured
by the HP5989B instrument. GCMS was reported on QP-2010 Plus.
N,N-diethylcinnamamide (3h): Solid; m.p. 60–62°C (Lit.27 m.p.
67–68°C); Z/E = 11:89. IR (KBr) (cm-1): 2971, 1689, 1644, 1515,
1
977, 756. H NMR (300 MHz, CDCl3/TMS): G 1.18 (m, 6 H), 3.45
(m, 4 H), 6.80 (d, 1 H, J = 15.4 Hz), 7.37 (m, 3 H), 7.50 (m, 2H),
7.69 (d, 1 H, J = 15.4 Hz) ppm. 13C NMR (75 MHz, CDCl3/TMS):
G = 13.19, 15.05, 41.06, 42.28, 117.78, 128.31, 128.75, 129.40,
135,47, 142.24, 165.68. MS: m/z (%) 203 (M+, 21), 131 (100), 103
(43), 77 (28), 44 (15). Elemental Anal. Calcd for C13H17NO: C,
76.81; H, 8.43; N, 6.89. Found: C, 76.99; H, 8.61; N, 7.03%.
3-(benzo[d][1,3]dioxol-5-yl)-N,N-diethylacrylamide (3i): Oil; Z/E
= 7:93. IR (KBr) (cm-1): 2975, 1643, 1593, 1493, 976, 811. 1H NMR
(300 MHz, CDCl3/TMS): G 1.24 (m, 6H), 3.46 (m, 4H), 5.97 (s,
2H), 6.66 (d, 1H, J = 15.4 Hz), 6.79 (d, 1H, J = 7.9), 6.99 (m, 2H),
7.62 (d, 1H, J = 15.4) ppm. 13C NMR (75 MHz, CDCl3/TMS):
G = 13.21, 15.04, 41.07, 42.25, 101.37, 106.34, 108.48, 115.74,
123.67, 129.88, 142.02, 148.15, 148.84, 165.80. MS: m/z (%)
247(M+, 44), 75 (100), 145 (45), 117 (16), 89 (26), 63 (9). Elemental
Anal. Calcd for C14H17NO3: C, 68.00; H, 6.93; N, 5.66. Found: C,
68.19; H, 7.07; N, 5.80%.
General procedure for the preparation of D, E-unsaturated
acetamide
Triphenylphosphine (1.2 mmol), N, N-diethyl chloroacetamide
(1.2 mmol), aldehydes (1.0 mmol) and Zn (1.2 mmol) were added into
DQꢀRYHQꢃGULHGꢀURXQGꢃERWWRPꢀÀDVNꢀꢄꢅꢆꢀP/ꢇꢁꢀ7KHꢀPL[WXUHꢀZDVꢀVWLUUHGꢀ
under microwave irradiation which was set at 1000W, and 150°C
IRUꢀꢆꢀPLQꢁꢀ7KHꢀSURGXFWꢀZDVꢀSXUL¿HGꢀE\ꢀFKURPDWRJUDSK\ꢀRQꢀVLOLFDꢀJHOꢀ
with ethyl acetate and petroleum ether (60–90°C). The physical and
spectra data of all compounds are as follows.
N,N-diethyl-3-(furan-2-yl)acrylamide (3j): Oil; Z/E
= 10:90.
IR (KBr) (cm-1): 2980, 1645, 1595, 980, 815. 1H NMR (300 MHz,
CDCl3/TMS): G 1.21 (m, 6 H), 3.47 (m, 4 H), 6.55 (m, 2 H), 6.73
(d, 1 H), 7.45 (m, 2 H) ppm. 13C NMR (75 MHz, CDCl3/TMS):
G = 13.20, 15.05, 41.06, 42.25, 112.07, 113.50, 115.32, 129.08, 143.67,
151.81, 165.53. MS: m/z (%) 193(M+, 20), 121 (100), 72 (15), 65 (32).
N,N-diethyl-5-phenylpenta-2,4-dienamide (3k): Oil; Z/E = 12:88.
N,N-diethyl-3-(4-nitrophenyl)acrylamide (3a): Pale yellow solid;
m.p. 142–145°C (Lit.27 m.p. 151–152°C); Z/E = 10:90. IR (KBr)
(cm-1): 2975, 1648, 1605, 975, 813, 725. 1H NMR (300 MHz, CDCl3/
TMS): G 1.26 (m, 6 H), 3.51 (m, 4 H), 6.95 (d, 1 H, J = 15.4 Hz), 7.65
(d, 2 H, J = 8.8 Hz), 7.73 (d, 1 H, J = 15.4 Hz), 8.23 (d, 2 H, J = 8.7 Hz)
ppm. 13C NMR (75 MHz, CDCl3/TMS): G = 13.10, 15.14, 41.22,
42.39, 123.67, 124.09, 128.26, 139.55, 141,74, 143.99, 164.68. MS:
m/z (%) 248 (M+, 46), 233 (29) 176 (99), 130 (37), 102 (36), 77 (10),
58 (17). Elemental Anal. Calcd for C13H16N2O3: C, 62.89; H, 6.50;
N, 11.28. Found: C, 63.05; H, 6.61; N, 11.41%.
1
IR (KBr) (cm-1): 2970, 1655, 1615, 975, 760. H NMR (300 MHz,
CDCl3/TMS): G 1.18 (m, 6 H), 3.45 (m, 4 H), 6.38 (d, 1 H, J = 15 Hz),
6.88 (d, 1 H, J = 15 Hz), 7.47, (m, 7 H) ppm. 13C NMR (75 MHz,
CDCl3/TMS): G = 13.19, 14.96, 41.05, 42.27, 120.90, 126.95, 128.56,
128.86, 130.00, 136.43, 138.83, 142.54, 165.93. MS: m/z (%) 229
(M+, 31), 157 (100), 128 (67), 115 (13), 77 (11), 58 (7).
N,N-diethyl-3-(4-chlorophenyl)acrylamide (3b): Oil; Z/E = 9:91.
IR (KBr) (cm-1): 2975, 1648, 1606, 1489, 975, 817. 1H NMR (300

26 JOURNAL OF CHEMICAL RESEARCH 2009
3
4
X.C. Yu and X. Huang, Synlett, 2002, 11, 1895.
J.L. Wu, H.F. Wu, S.Y. Wei and W.M. Dai, Tetrahedron Lett., 2004, 45,
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N,N-diethyl-5-phenylpent-2-enamide (3l): Oil; Z/E = 9:91. IR (KBr)
(cm-1): 2975, 1655, 1610, 970, 760. 1H NMR (300 MHz, CDCl3/
TMS): G 1.10 (m, 6 H), 2.52 (m, 2 H), 2.75 (m, 2 H), 3.34 (m, 4 H),
6.15 (d, 1 H, J = 15 Hz), 6.89 (m, 1 H), 7.23 (m, 5 H). 13C NMR
(75 MHz, CDCl3/TMS): G = 13.12, 14.74, 30.88, 34.65, 40.80,
42.13, 121.21, 122.82, 126.13, 128.38, 141.11, 165.92. MS: m/z (%)
231(M+, 44), 159 (19), 126 (51), 100 (24), 91 (100), 72 (43), 58 (39).
N,N-diethylhex-2-enamide (3m):Oil; Z/E = 16:84. IR (KBr) (cm-1):
2969, 1656, 1615, 1447, 974, 820. 1H NMR(300 MHz, CDCl3/TMS):
G 0.96 (m, 3H), 1.20 (m, 6H), 1.44 (m, 2H), 2.14 (q, 2H), 3.47 (m,
4H), 6.15 (d, 1H, J = 16 Hz), 6.88 (m, 1H) ppm. 13C NMR (75 MHz,
CDCl3/TMS): G = 13.07, 14.50, 14.70, 23.15, 34.20, 40.75, 42.08,
120.93, 140.89, 165.41. MS: m/z (%) 169 (M+,65), 154 (100), 126
(80), 97 (75), 72 (36), 58 (55), 55 (85).
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We thank the Natural Science Foundation of Zhejiang
Province (Y205540), the Education Foundation of Zhejiang
Province (20051284), the Foundation of Wenzhou Municipal
6FLHQFHꢀDQGꢀ7HFKQRORJ\ꢀ%XUHDXꢀꢄ1ꢅꢈꢈꢉꢈꢈꢆꢅꢇꢀIRUꢀWKHꢀ¿QDQFLDOꢀ
support.
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Received 22 October 2008; accepted 10 November 2008
Paper 08/0241 doi: 10.3184/030823409X393682
Published online: 16 January 2009
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