Synthesis and herbicidal activity of N-aryl-2-heteroaryloxy-N-isopropyl acetamide

Article abstract of DOI:10.14233/ajchem.2013.15239

A series of novel N-aryl-2-heteroaryloxy-N-isoproylacetamide derivatives were synthesized by multi-step reactions. Their structures were characterized by ¹H NMR, MS and elemental analyses. The target compounds were evaluated for their herbicidal activities against Echinochloa crusgalli, Digitaria sanguinalis Scop., Abutilon theophrasti, Setaria viridis, Zinnia elegans and Acalypha australis. The results indicated that some of the title compounds displayed excellent herbicidal activities.

Full text of DOI:10.14233/ajchem.2013.15239

Asian Journal of Chemistry; Vol. 25, No. 12 (2013), 6931-6934
http://dx.doi.org/10.14233/ajchem.2013.15239
Synthesis and Herbicidal Activity of N-Aryl-2-heteroaryloxy-N-isopropyl acetamide
1,*
1
1
1
1
2
QING YE , XIAO-BO ZHU , KAI GU , XIAO-QUAN NI , JIAN-RONG GAO and MIAO WEI-RONG
1College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310014. P.R. China
2College of Chemical Engineering, Dalian University of Technology, Dalian 111024, P.R. China
*Corresponding author: E-mail: yeqing1975@zjut.edu.cn
(Received: 29 January 2013;
Accepted: 7 June 2013)
AJC-13603
A series of novel N-aryl-2-heteroaryloxy-N-isoproylacetamide derivatives were synthesized by multi-step reactions. Their structures
were characterized by 1H NMR, MS and elemental analyses. The target compounds were evaluated for their herbicidal activities against
Echinochloa crusgalli, Digitaria sanguinalis Scop., Abutilon theophrasti, Setaria viridis, Zinnia elegans and Acalypha australis. The
results indicated that some of the title compounds displayed excellent herbicidal activities.
Key Words: N-Aryl-2-heteroaryloxy-N-isopropyl acetamide, Aryloxyacetamide, Synthesis, Herbicidal activity.
chromatography (TLC). All reagents were obtained from
commercial sources and used without further purification
unless stated.
Synthesis of compounds: The title compounds were
synthesized according to the route as shown in Fig. 1. The
intermediate 26, 37, 48, 2-chlorobenzo[d]thiazole9, 2-chloro-
4,6-dimethoxy-1,3,5-triazine10 and 2-(methylsulfonyl)-5-
(trifluoro-methyl)-1,3,4-thiadiazole11 are synthesized.
INTRODUCTION
Recent years, heterocyclic compounds had received
considerable attentions in medicinal and pesticidal fields1.
Aryloxyacetamide derivatives2 have been widely studied in
recent years because of its outstanding biological activity, high
selectivity, easy degradation and safety for the plants. Among
them, some compounds have been developed as commercial
herbicides, such as napropamide and flufenacet, which exhibited
excellent activities. Furthermore, it is reported that many
heterocyclic compounds with nitrogen-containing hetero-
cycles, especially thiadiazole3, benzothiazole4 and triazine5,
possess a diverse range of functions. For example, thiadiazoles,
benzothiazoles and triazines displayed herbicidal, fungicidal,
insecticidal, anticancer and antiinflammatory activities. In view
of these facts and also as a part of our work on the development
of bioactive heterocyclic compounds, herein we reported the
synthesis, characterization and biological of a series of aryloxy-
acetamide derivatives containing a thiadiazole, benzothiazole
or triazine moiety.
O
H
N
Cl
NH2
ClCOCH2Cl
CH3COCH3
NaBH4
N
R
R
R
1
2
3
O
O
Ar
OH
O
ArCl or ArSO2CH3
KOAc
N
N
R
R
CH3OH
4
R = 4-F, 4-CF3, 2-Cl-4-F, 2-F-4-Cl-5-Cyclopentyloxyl
5
N
N
S
N
N
N
Ar =
CF3
S
MeO
N
OMe
EXPERIMENTAL
Fig. 1. Synthsis route for compounds 5a-5j
Melting points were determined with a BÜCHI Melting
Point B-450 apparatus (Büchi Labortechnik, Switzerland). The
1H NMR spectra were recorded in DMSO-d6 or CDCl3 on
Bruker Avance DMX 500 at 500 MHz (chemical shifts are
expressed as δ values relative to TMS as internal standard).
ESI (positive) was recorded on an Esquire-LC-00075 spectro-
meter. Element analyses were performed on an Eager 300
instrument. All reactions were monitored by thin-layer
General procedure for the synthesis of N-aryl-N-iso-
propyl-2-(5-(trifluoromethyl)-1,3,4-thiadiazol-2-yloxy)-
acetamide (5a-c): A mixture of N-aryl-2-hydroxyl-N-isoproyl-
acetamide (4) (10 mmol), 2-(methylsulfonyl)-5-(trifluoro-
methyl)-1,3,4-thiadiazole (10 mmol), tetraethylammonium
bromide (1 mmol), anhydrous potassium carbonate (10.1
mmol) and acetone (20 mL) was stirred at room temperature

6932 Ye et al.
Asian J. Chem.
for 20 h. After that, the mixture was filtered and the filtrate
was concentrated in vacuo. The residue was recrystallized from
ethanol to afford 5a-c.
2-(Benzo[d]thiazol-2-yloxy)-N-(4-chloro-5-(cyclopentyl-
oxy)-2-fluorophenyl)-N-isopropylacetamide (5g): White
solid, m.p. 70-72 ºC, yield 74.5 %; H NMR (CDCl3, 500
1
N-(2-Chloro-4-fluorophenyl)-N-isopropyl-2-(5-(tri-
fluoromethyl)-1,3,4-thiadiazol-2-yloxy)acetamide (5a):
White solid, m.p. 87-89 ºC, yield 61.5 %; 1H NMR (CDCl3,
500 MHz), δ: 1.05 (d, J = 7.0 Hz, 3H), 1.26 (d, J = 7.0 Hz,
3H), 4.69-4.88 (m, 3H), 7.13-7.17 (m, 1H), 7.33-7.35 (dd, J =
7.5, 2.5 Hz, 1H), 7.41-7.44 (m, 1H); MS (ESI), m/z: 398
(M+1)+. Elemental anal. (%), calculated: C, 42.29; H, 3.41;
N, 10.53; found: C, 42.27; H, 3.34; N, 10.56.
N-Isopropyl-2-(5-(trifluoromethyl)-1,3,4-thiadiazol-2-
yloxy)-N-(4-(trifluoromethyl)phenyl)acetamide (5b):White
solid, m.p. 100-102 ºC, yield 50.9 %; 1H NMR (CDCl3, 500
MHz), δ: 1.12 (d, J = 6.5 Hz, 6H), 4.32 (s, 2H), 4.96-5.01 (m,
1H), 7.41 (d, J = 8.0 Hz, 2H), 7.79 (d, J = 8.0 Hz, 2H); MS
(ESI), m/z: 414 (M+1)+. Elemental anal. (%), calculated: C,
43.59; H, 3.17; N, 10.17; found: C, 43.74; H, 3.15; N, 10.05.
N-(4-Chloro-5-(cyclopentyloxy)-2-fluorophenyl)-N-
isopropyl-2-(5-(trifluoromethyl)-1,3,4-thiadiazol-2-yloxy)-
acetamide (5c): White solid, m.p. 79-81 ºC, yield 54.7 %; 1H
NMR (CDCl3, 500 MHz), δ: 1.05 (d, J = 7.0 Hz, 3H), 1.18 (d,
J = 7.0 Hz, 3H), 1.64-1.68 (m, 2H), 1.82-1.89 (m, 6H), 3.70-
3.77 (m, 2H), 4.72-4.74 (m, 1H), 4.93-4.98 (m, 1H), 6.69 (d,
J = 7.0 Hz,1H), 7.25 (d, J = 9.0 Hz, 1H); MS (ESI), m/z: 482
(M+1)+. Elemental anal. (%), calculated: C, 47.36; H, 4.18;
N, 8.72; found: C, 47.18; H, 4.03; N, 8.83.
MHz), δ: 1.08 (d, J = 7.0 Hz, 3H), 1.20 (d, J = 7.0 Hz, 3H),
1.63-1.68 (m, 2H), 1.86-1.95 (m, 6H), 4.72 (d, J = 14.0 Hz,
1H), 4.77-4.80 (m,1H), 4.89 (d, J = 14.0 Hz, 1H), 4.97-5.02
(m, 1H), 6.86 (d, J = 7.0 Hz, 1H), 7.20-7.24 (m, 1H), 7.30-
7.36 (m, 2H), 7.59-7.65 (m, 2H); MS (ESI), m/z: 463 (M+1)+.
Elemental anal. (%), calculated: C, 59.67; H, 5.23; N, 6.05;
found: C, 59.55; H, 5.19; N,6.00.
General procedure for the synthesis of N-Aryl-2-(4,6-
dimethoxy-1,3,5-triazin-2- yloxy)-N-isopropylacetamide
(5h-j): A mixture of N-aryl-2-hydroxyl-N-isoproylacetamide
(4) (7.5 mmol), 2-chloro-4,6-dimethoxy-1,3,5-triazine (7.5
mmol), anhydrous potassium carbonate (7.5 mmol) and toluene
(20 mL) was refluxed for 20 h. After cooling, the mixture was
filtered and the filtrate was concentrated in vacuo. The residue
was recrystallized from acetone/hexane to get 5h-j.
2-(4,6-Dimethoxy-1,3,5-triazin-2-yloxy)-N-(4-fluoro-
phenyl)-N-isopropylacetamide (5h): White solid, m.p. 118-
120 ºC, yield 82.5 %; 1H NMR (CDCl3, 500 MHz), δ: 1.07 (d,
J = 7.0 Hz, 6H), 4.01 (s, 6H), 4.53 (s, 2H), 4.92-4.97 (m, 1H),
7.14-7.18 (m, 2H), 7.23-7.26 (m, 2H); MS (ESI), m/z: 351
(M+1)+. Elemental anal. (%), calculated: C, 54.85; H, 5.47;
N, 15.99; found: C, 54.73; H, 5.54; N,15.82.
2-(4,6-Dimethoxy-1,3,5-triazin-2-yloxy)-N-isopropyl-
N-(4-(trifluoromethyl)phenyl)acetamide (5i): White solid,
m.p. 109-111 ºC, yield 85.4 %; 1H NMR (CDCl3, 500 MHz),
δ: 1.10 (d, J = 7.0 Hz, 6H), 4.02 (s, 6H), 4.52 (s, 2H), 4.92-
4.97 (m, 1H), 7.43 (d, J = 8.0 Hz, 2H), 7.76 (d, J = 8.0 Hz,
2H); MS (ESI), m/z: 401 (M+1)+. Elemental anal. (%), calcu-
lated: C, 51.00; H, 4.78; N, 13.99; found: C, 50.82; H, 4.83;
N,14.06.
General procedure for the synthesis of N-aryl-2-(benzo-
[d]thiazol-2-yloxy)-N-isopropylacetamide (5d-g): 2-Chloro-
benzo[d]thiazole (15.6 mmol) was added dropwise to a mixture
of N-aryl-2-hydroxyl-N-isoproylacetamide (4) (15.6 mmol),
potassium hydroxide (26.8 mol) and isopropanol (20 mL) at
0-5 ºC. After addition, the mixture was stirred for 3 h at room
temperature, then poured into ice water. The generated solid
was collected by filtration and recrystallized from ethanol to
get 5d-g.
N-(4-Chloro-5-(cyclopentyloxy)-2-fluorophenyl)-2-
(4,6-dimethoxy-1,3,5-triazin-2-yloxy)-N-isopropylacetamide
1
(5j): White solid, m.p. 148-150 ºC, yield 85.4 %; H NMR
2-(Benzo[d]thiazol-2-yloxy)-N-(4-fluorophenyl)-N-iso-
propylacetamide (5d): White solid, m.p. 100-102 ºC, yield
81.5 %; 1H NMR (CDCl3, 500 MHz), δ: 1.09 (d, J = 7.0 Hz,
6H), 4.71 (s, 2H), 4.90-5.05 (m, 1H), 7.17-7.22 (m, 3H), 7.27-
7.29 (m, 2H), 7.33-7.36 (m, 1H), 7.62-7.64 (m, 2H); MS (ESI),
m/z: 345 (M+1)+. Elemental anal. (%), calculated: C, 62.77;
H, 4.98; N, 8.13; found: C, 62.98; H, 5.01; N, 7.99.
(CDCl3, 500 MHz), δ: 1.05 (d, J = 7.0 Hz, 3H), 1.17 (d, J =
7.0 Hz, 3H), 1.63-1.68 (m, 2H), 1.86-1.91 (m, 6H), 4.00 (s,
6H), 4.58-4.66 (m, 2H), 4.78-4.80 (m, 1H) 4.93-4.96 (m, 1H),
6.86 (d, J = 7.0 Hz, 1H), 7.25 (d, J = 7.0 Hz,1H); MS (ESI),
m/z: 469 (M+1)+. Elemental anal. (%), calculated: C, 53.79;
H, 5.59; N, 11.95; found: C, 53.65; H, 5.62; N, 11.81.
Herbicidal activities assay
2-(Benzo[d]thiazol-2-yloxy)-N-(2-chloro-4-fluorophenyl)-
N-isopropylacetamide (5e): White solid, m.p. 98-100 ºC,
yield 77.9 %; 1H NMR (CDCl3, 500 MHz), δ: 1.05 (d, J = 7.0
Hz, 3H), 1.27 (d, J = 7.0 Hz, 3H), 4.67-4.79 (m, 2H), 4.87-
4.93 (m, 1H), 7.12-7.16 (m, 1H), 7.20-7.24 (m, 1H), 7.32-
7.37 (m, 2H), 7.40-7.43 (m, 1H), 7.60-7.64 (m, 2H); MS (ESI),
m/z: 379 (M+1)+. Elemental anal. (%), calculated: C, 57.07;
H, 4.26; N, 7.39; found: C, 57.07.55; H, 4.27; N, 7.31.
2-(Benzo[d]thiazol-2-yloxy)-N-isopropyl-N-(4-(tri-
fluoromethyl)phenyl)acetamide (5f): White solid, m.p. 112-
114 ºC, yield 83.3 %; 1H NMR (CDCl3, 500 MHz), δ: 1.13 (d,
J = 7.0 Hz, 6H), 4.72 (s, 2H), 5.03-5.06 (m, 1H), 7.21-7.24
(m, 1H), 7.33-7.37 (m, 1H), 7.46 (d, J = 8.0 Hz, 2H), 7.62-
7.64 (m, 2H), 7.78 (d, J = 8.0 Hz, 2H); MS (ESI), m/z: 395
(M+1)+. Elemental anal. (%), calculated: C, 57.86; H, 4.34;
N, 7.10; found: C, 58.01; H, 4.40; N, 7.02.
Three dicotyledonous weeds, viz., Abutilon theophrasti,
Zinnia elegans and Acalypha australis, and three monocoty-
ledonous crops, viz., Echinochloa crusgalli and Digitaria
sanguinalis and Setaria viridis, were used to test the herbicidal
activities of the title compounds. Acetochlor was obtained as
a commercial material.
Culture method: The seeds were planted in 8 cm diameter
plastic boxes containing artificial mixed soil. Before plant
emergence, the boxes were covered with plastic film to retain
moisture. Plants were grown in the green house. The fresh
weight of the above ground tissues was measured 17 days after
treatment. The inhibition per cent was used to describe the
control efficiency of the compounds.
Treatment: The dosage (activity ingredient) for each
compound is corresponded to 750 g/ha. The purified comp-
ounds were dissolved in 100 µL of N,N-dimethylformamide

Vol. 25, No. 12 (2013)
Synthesis and Herbicidal Activity of N-Aryl-2-heteroaryloxy-N-isopropyl acetamide 6933
TABLE-1
HERBICIDAL ACTIVITY OF TITLE COMPOUNDS in vivo (750 g/hm2)
Echinochloa
crusgalli
Setaria
viridis
Digitaria
sanguinalis
Acalypha
australis
Abutilon
theophrasti
Zinnia
elegans
Compd.
No.
A
B
A
B
A
B
A
B
A
B
A
B
5a
68.60
30.00
23.60
43.96
33.38
54.71
19.81
29.70
36.37
38.22
97.04
79.14
19.68
52.11
6.67
37.92
31.67
2.11
81.58
75.40
52.71
53.80
26.76
94.35
74.05
56.28
30.16
52.68
97.44
72.74
25.84
27.74
66.67
45.17
29.58
16.74
20.69
34.12
94.78
90.18
73.13
79.12
62.62
48.08
82.31
83.10
56.04
61.05
22.10
100
100
55.74
63.08
50.35
45.15
69.41
59.64
74.08
80.47
36.33
80.95
100
100
56.12
70.85
56.25
58.79
39.46
70.48
28.59
20.32
26.85
4.73
4.07
9.48
7.59
11.48
32.22
3.52
30.92
10.55
2.22
75.07
60.08
48.38
69.43
68.23
83.99
51.09
48.27
53.24
44.64
54.20
52.67
49.94
35.22
39.97
45.96
25.90
24.97
28.13
43.67
21.34
5b
5c
29.77
49.77
23.25
40.00
3.26
15.81
15.81
7.44
100
71.21
62.83
8.33
16.67
48.48
56.06
12.88
2.27
100
5d
5e
5f
5g
5h
5i
5j
6.92
0.85
98.52
8.70
12.34
Acetochlor
A = Postmergence; B = Premergence
with 0.1 µL of Tween 20 and then prepared for spraying with
a laboratory belt sprayer delivering a 750 L/ha spray volume.
Compounds and Acetochlor were sprayed immediately after
seed planting (preemergence treatment) or after the expansion
of the first true leaf (postemergence treatment). The mixture
of same amount of water, N,N-dimethylformamide and Tween
20 was sprayed as the blank. Each treatment was triplicated.
The activity numbers represented the per cent displaying
herbicidal damage as compared to the blank. The error of the
experiments was 2 %.
and 5f (94.35 %) displayed good control effect against
Setaria viridis. The data given in Table-1 indicated that the
change of heterocycles affects the herbicidal activity. These
compounds have lower herbicidal activities with the benzo[d]-
thiazole, triazine than with thiadiazole. It is benefit to further
design work.
Conclusion
A series of new aryloxyacetamides with a heterocycle
moiety was designed and synthesized. Their structures were
confirmed through 1H NMR, ESI-MS and Elemental analysis.
The herbicidal activity results show that some of these
compounds had good herbicidal activity against Echinochloa
crusgalli, Setaria viridis, Digitaria sanguinalis scop, Acalypha
australis, Abutilon theophrasti and Zinnia elegans.
RESULTS AND DISCUSSION
A group of 10 new aryloxyacetamide derivatives was
synthesized from substituted arylamines by the process of
N-alkylation, N-acylation, esterification, transesterification and
condensation reactions. To reducing impurities in the process
of synthesizing amide 3, nitrogen gas was bubbled into the
reaction system to remove the generated HCl, instead of using
acid blinding agent such as pyridine, triethylamine, potassium
carbonate or sodium hydroxide base. N-Aryl-2-hydroxyl-N-
isoproylacetamide 4 was prepared by one-pot reaction by using
compound 3, potassium acetate and methanol as reactants. This
method has the advantages of good yields, short reaction time
and mild reaction conditions.
Herbicidal activity: Herbicidal activities of target
compounds 5a-j against Echinochloa crusgalli, Setaria viridis,
Digitaria sanguinalis Scop, Acalypha australis, Abutilon
theophrasti and Zinnia elegans were summarized in Table-1.
From the Table-1, it is indicated that compounds had better
activity under the premergence condition than that of
postmergence. Compounds 5a and 5b have excellent herbicidal
activities against Acalypha australis and Digitaria sanguinalis
(100 %) under the premergence condition. Under the
postmergence, however, same herbicidal acitivities were
observed for compound 5a and 5b has moderate effects on
the Echinochloa crusgalli, Setaria viridis, Digitaria sanguinalis
Scop, Acalypha australis, Abutilon theophrasti and Zinnia
elegans.All these compounds did not display obvious herbicidal
activities against Abutilon theophrasti and Zinnia elegans. For
the Setaria viridis, it was indicated that most of the compounds
had weak herbicidal activity, except that compound 5a (81.58 %)
ACKNOWLEDGEMENTS
The authors gratefully acknowledged the financial support
from the Natural Science Foundation of China (21176223)
and the National Natural Science Foundation of Zhejiang
(Y407306).
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