Synthesis and Fungicidal Activity of Substituted (E)-3-Phenyl-1-(pyridin-3-yl)prop-2-en-1-one (E,Z)-O-Alkyl- and O-Benzyloximes

Article abstract of DOI:10.1134/S1070428019070078

Previously unknown substituted (E)-3-phenyl-1-(pyridin-3-yl)prop-2-en-1-one (E,Z)-O-alkyl- and O-benzyloximes were synthesized by oximation of (E)-3-phenyl-1-(pyridin-3-yl)prop-2-en-1-ones (azachalcones), followed by alkylation of the resulting oximes und

Full text of DOI:10.1134/S1070428019070078

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2019, Vol. 55, No. 7, pp. 964–968. © Pleiades Publishing, Ltd., 2019.
Russian Text © The Author(s), 2019, published in Zhurnal Organicheskoi Khimii, 2019, Vol. 55, No. 7, pp. 1063–1068.
Synthesis and Fungicidal Activity of Substituted
(E)-3-Phenyl-1-(pyridin-3-yl)prop-2-en-1-one (E,Z)-O-Alkyl-
and O-Benzyloximes
A. V. Kuzenkova* and V. V. Zakharycheva
a Mendeleev University of Chemical Technology of Russia, Moscow, Russia
*e-mail: kuzalex71@yandex.ru
Received December 13, 2018; revised February 10, 2019; accepted February 20, 2019
Abstract—Previously unknown substituted (E)-3-phenyl-1-(pyridin-3-yl)prop-2-en-1-one (E,Z)-O-alkyl- and
O-benzyloximes were synthesized by oximation of (E)-3-phenyl-1-(pyridin-3-yl)prop-2-en-1-ones (aza-
chalcones), followed by alkylation of the resulting oximes under different conditions. The synthesized
compounds showed a good fungicidal activity.
Keywords: 3-phenyl-1-(pyridin3-yl)prop-2-en-1-ones, azachalcone oximes, O-alkylation of oximes, phase-
transfer catalysis, E,Z isomerism of oximes, fungicidal activity.
DOI: 10.1134/S1070428019070078
Oxime ethers derived from heterocyclic ketones
attract interest due to their potential biological activity.
For example, pyrifenox (1) has found application as
a fungicide with a broad spectrum of action on berry
and fruit plants and grape [1], and oxiconasole (2) is
used for the treatment of superficial mycoses in
humans [2]. These compounds inhibit biosynthesis of
fungal ergosterol via coordination of the heteroatom to
the iron atom in the active site of cytochrome oxidase
(CYP51) [1]. Another class of oxime ethers includes
fluoxastrobin (3) and kresoxim-methyl (4) that are
widely used to treat crops, vegetables, and fruits [3].
Compounds 3 and 4 bind to cytochrome bc1 complex
thus blocking fungal cell respiration. In recent years,
increasing interest is observed to the synthesis of new
O-substituted oximes due to their valuable fungicidal
properties. 3-Aryl-1-(indol-3-yl)prop-2-en-1-one O-al-
kyloximes [4], 3,3-dimethyl-1-(pyridin-3-yl)butan-2-
one O-benzoyloximes [5], and 3-phenyl-1-(pyridin-3-
yl)propan-1-one O-alkyloximes [6] showed fungicidal
activity. We previously synthesized (Z)-N′-methoxy-
pyridine-3-carboximidamides [7, 8] and substituted
(pyridin-3-yl)methanone (E,Z)-O-alkyloximes [9],
studied their steric structure, and revealed fungicidal
activity of these compounds. In continuation of these
studies, herein we report the synthesis of a series of
new 3-phenyl-1-(pyridin-3-yl)prop-2-en-1-one O-al-
kyl- and O-benzyloximes 5a–5i and their fungicidal
activity.
Target compounds 5a–5i were synthesized from the
corresponding oximes 7a–7c which were prepared
according to a conventional procedure, by treatment of
azachalcones 6a–6c with hydroxylamine hydrochloride
in aqueous ethanol (Scheme 1). Initial azachalcones
6a–6c were obtained in turn by condensation of
3-acetylpyridine with 4-halobenzaldehydes in the
presence of 10% sodium hydroxide [10]. The progress
of the oximation of 6a–6c and the purity of 7a–7c were
monitored by TLC and IR spectroscopy (following the
disappearance of the carbonyl stretching vibration
band at 1660 cm–1).
Taking into account that alkylating agents with
different reactivities were used for the alkylation of
7a–7c, the reactions were performed under different
conditions. The benzylation was carried out in a two-
phase system (benzene–5% aqueous KOH) using
benzyl(triethyl)ammonium chloride as phase-transfer
catalyst. However, the alkylation involved not only the
oxime functionality but also pyridine nitrogen atom.
Furthermore, the reaction was accompanied by hydrol-
ysis of benzyl chloride. As a result, in no case we
succeeded in attaining complete conversion of the
initial oxime; nevertheless, compounds 5a–5c were
isolated in acceptable yields (46.0–69.6%).
964

SYNTHESIS AND FUNGICIDAL ACTIVITY OF SUBSTITUTED (E)-3-PHENYL-...
965
Cl
Cl
Cl
Cl
O
O
N
N
F
Cl
N
N
N
O
OMe
O
N
N
OMe
O
N
N
Cl
Cl
1
2
3
O
MeO
N
OMe
O
Me
4
Weaker alkylating agents such as hexyl bromide
and cyclohexyl bromide required the use of a stronger
base, sodium hydride in DMF. The yields of O-cyclo-
hexyloximes 5g–5i (13.6–31.5%) were appreciably
lower than the yields of their O-hexyl analogs 5d–5f
(65.5–74.9%), presumably due to steric hindrances and
facile elimination of hydrogen bromide from cyclo-
hexyl bromide.
The unreacted oxime was separated from the
alkylation product and solvent by repeated washing
with water and 15% aqueous potassium hydroxide.
The products were finally purified by dry-column flash
chromatography [11] on silica gel (5–40 μm).
7.7–9.7 Hz). The signals were assigned to particular
isomers by comparing with the data reported in [4] for
3-aryl-1-(indol-3-yl)prop-2-en-1-one O-alkyloximes
whose structure was firmly established. Signals of the
E isomers were located downfield from those of the Z
isomers. The C=C double bond in all compounds 5a–
5i retained its original E configuration, as followed
1
from the corresponding H–1H coupling constant
(3Jtrans = 16.1–17.3 Hz).
Compounds 5a–5i were evaluated for their in vivo
fungicidal activity against five pathogenic fungal cul-
tures belonging to asco-, basidio-, and deuteromycetes:
Venturia inaequalis (Cooke) Winter, Rhizoctonia
solani Kühn, Fusarium oxysporum Schlecht, Fusarium
moniliforme Sheldon, and Helminthosporium sativum
Pammel King et Bakke from the collection of the All-
Russian Research Institute of Chemical Means of Plant
Protection. Experiments were performed according to
a standard procedure [12] using commercial fungicides
kresoxim-methyl (4) and triadimefon [1-(4-chloro-
phenoxy)-3,3-dimethyl-1-(1H-1,2,4-triazol-1-yl)butan-
2-one] as references. It was found that all compounds
showed fungicidal activity. The activity of the most
Compounds 5a–5i were mixtures of E and Z
isomers at different ratios. The formation of mixtures
of isomeric O-alkyloximes was also reported in [4].
Signals of the Z and E isomers were distinguishable in
1
the H NMR spectra, and we were able to estimate
their ratios by the signal intensities. For this purpose, it
was most convenient to use signals of protons at the
C=C double bond, which appeared as two pairs of AB
doublets, as well as signals of 4-H of the pyridine ring
(two doublets with spin–spin coupling constants of
Scheme 1.
X
X
X
5
2
6
4
i
ii–iv
2'
3
N
N
N
3'
O
N
N
OH
OR
6a, 6c
7a, 7c
5a–5i
5, R = PhCH2 (a–c), C6H13 (d–f), cyclo-C6H11 (g–i); X = F (a, d, g), Cl (b, e, h), Br (c, f, i); 6, 7, X = F (a), Cl (b), Br (c).
Reagents and conditions: i: NH2OH·HCl, EtOH, water bath; ii: PhCH2Cl, PhH–5% aq. NaOH, BTEAC, reflux;
iii: C6H13Br, NaH, DMF, 20–60°C; iv: cyclo-C6H11Br, NaH, DMF, 20–60°C.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 7 2019

KUZENKOV, ZAKHARYCHEV
966
Table 1. Radial growth inhibition (% with respect to control) of fungal mycelium in vivo in the presence of compounds 5a–5i
at a concentration of 30 mg/L
Compound no.
V. inaequalis
R. solani
F. oxysporum
F. moniliforme
H. sativum
5a
5b
5c
5d
5e
5f
33±5
28±3
35±5
33±6
28±2
25±3
28±5
23±4
55±1
100
48±6
54±5
–
22±6
60±5
18±5
17±5
11±2
16±2
46±2
48±2
45±2
58±4
72±5
43±3
90±1
30±4
44±3
27±2
31±5
49±4
53±2
66±2
57±3
85±7
56±2
60±2
46±3
37±2
28±2
37±5
43±5
46±3
60±5
93±2
60±5
3±2
0
27±5
14±4
59±2
45±2
94±1
54±4
5g
5h
5i
4
Triadimefon
60±5
active derivatives, O-benzyloxime 5b and O-cyclo-
hexyloximes 5h and 5i was comparable to that of the
reference fungicides and in some cases exceeded it.
Compounds 7b and 7c were synthesized in a simi-
lar way.
[(2E)-3-(4-Chlorophenyl)-1-(pyridin-3-yl)prop-2-
en-1-ylidene]hydroxylamine (7b). Yield 1.106 g
(85.6%), mp 147–149°C.
EXPERIMENTAL
[(2E)-3-(4-Bromophenyl)-1-(pyridin-3-yl)prop-
2-en-1-ylidene]hydroxylamine (7c). Yield 0.406 g
(66.8%), mp 164–166°C.
1
The H NMR spectra were recorded on a Bruker
AM 300 spectrometer at 300 MHz from solutions in
DMSO-d6. The IR spectra were measured in mineral
oil on an IKS-29 spectrometer.
(1EZ,2E)-N-Benzyloxy-3-(4-fluorophenyl)-
1-(pyridin-3-yl)prop-2-en-1-imine (5a). A solution of
0.300 g (2.37 mmol) of benzyl chloride and 0.23 g
(1 mmol) of benzyl(triethyl)ammonium chloride
(BTEAC) in 10 mL of benzene was added to a solution
of 0.484 g (2 mmol) of oxime 7a in 5% aqueous
potassium hydroxide [1.43 g (25.5 mmol) of KOH in
28 mL of water]. The two-phase system was vigor-
ously stirred for 5 h under reflux, the progress of the
reaction being monitored by TLC. The mixture was
cooled to room temperature, and the organic layer was
separated, dried over sodium sulfate, and evaporated.
The residue was purified by flash chromatography on
silica gel (5–40 μm) using methylene chloride–ethyl
acetate (1:1) as eluent. Yield 0.069 g (69.6%), E/Z
Initial (E)-3-phenyl-1-(pyridin-3-yl)prop-2-en-1-
ones 6a–6c were synthesized by condensation of
3-acetylpyridine with 4-halobenzaldehydes [10].
[(2E)-3-(4-Fluorophenyl)-1-(pyridin-3-yl)prop-
2-en-1-ylidene]hydroxylamine (7a). A solution of
0.695 g (10 mmol) of hydroxylamine hydrochloride in
1 mL of water was added to a solution of 1.135 g
(5 mmol) of (E)-3-(4-fluorophenyl)-1-(pyridin-3-yl)-
prop-2-en-1-one (6a) in 15 mL of ethanol. The mixture
was heated for 1 h on a water bath and cooled to room
temperature, a solution of 0.400 g (10 mmol) of
sodium hydroxide in 1 mL of water was added, and
carbon dioxide was passed through the mixture until
pH ~7. The precipitate was filtered off, treated with
5 mL of boiling methanol, 5 mL of tetrahydrofuran
was added, the mixture was cooled to room tempera-
ture, and the precipitate was filtered off. The filtrate
was evaporated to dryness, and the residue was
recrystallized from ethanol. Yield 0.566 g (76.8%),
mp 130–132°C.
1
ratio 38:62, oily material. H NMR spectrum, δ, ppm
(J, Hz): 5.15 s (1.24H, OCH2, Z), 5.32 s (0.76H,
3
OCH2, E), 6.36 d and 7.06 d (1.24H, CH=CH, Z, J =
16.5), 6.68 d (0.38H, 3′-H, E, J = 16.9), 7.27–7.51 m
[9.38H, 2′-H (E), Harom], 7.56–7.68 m (1H, 5-H),
7.80 d (0.62H, 4-H, Z, J = 9.7), 7.91 d (0.38H, 4-H, E,
J = 8.1), 8.55 s (0.62H, 2-H, Z), 8.66 d (1H, 6-H, J =
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 7 2019

SYNTHESIS AND FUNGICIDAL ACTIVITY OF SUBSTITUTED (E)-3-PHENYL-...
967
4.8), 8.74 s (0.38N, 2-H, E). Found, %: C 75.50;
H 6.00; N 8.09. C21H17FN2O. Calculated, %: C 75.89;
H 5.16; N 8.43.
(0.20H, 4-H, Z, J = 8.1) 7.73 d (0.80H, 4-H, E, J =
8.1), 8.51 s (1H, 2-H), 8.66 d (1H, 6-H, J = 4.8).
Found, %: C 73.55; H 7.14; N 8.54. C20H23FN2O. Cal-
culated, %: C 73.42; H 7.19; N 8.48.
Compounds 5b and 5c were synthesized in a simi-
Compounds 5e–5i were synthesized in a similar
lar way.
way.
(1EZ,2E)-N-Benzyloxy-3-(4-chlorophenyl)-1-
(pyridin-3-yl)prop-2-en-1-imine (5b). Yield 0.307 g
(59.5%), E/Z = 45:55, red–brown oil. H NMR spec-
(1EZ,2E)-3-(4-Chlorophenyl)-N-hexyloxy-1-
(pyridin-3-yl)prop-2-en-1-imine (5e). Yield 0.489 g
(71.4%), E/Z = 64:36, yellow oil. H NMR spectrum,
δ, ppm (J, Hz): 0,81–0.95 m (3H, CH3), 1.19–1.39 m
[6H, CH3(CH2)3], 1.55–1.84 m (2H, CH2CH2O), 4.06–
4.29 m (2H, CH2O), 6.35 d and 7.05 d (0.72H,
CH=CH, Z, J = 16.5), 6.72 d and 7.54 d (1.28H,
CH=CH, E, J = 16.9), 7.27–7.44 m (5H, 5-H, Harom),
7.82 d (0.36H, 4-H, Z, J = 8.1), 8.35 d (0.64H, 4-H, E,
J = 8.1), 8.55 s (1H, 2-H), 8.65 d (1H, 6-H, J = 5.0).
Found, %: C 70.02; H 6.80; N 8.15. C20H23ClN2O.
Calculated, %: C 69.68; H 6.88; N 8.03.
1
1
trum, δ, ppm (J, Hz): 5.15 s (1.10H, OCH2, Z), 5.30 s
(0.90H, OCH2, E), 6.35 d and 7.03 d (1.10H, CH=CH,
Z, J = 16.5), 6.67 d and 7.54 d (0.90H, CH=CH, E,
3J = 16.5), 7.27–7.47 m [10.55H, 4-H (Z), 5-H, Harom],
7.80 d (0.45H, 4-H, E, J = 8.1), 8.55 s (0.45H, 2-H, Z),
8.66 s (1H, 6-H), 8.74 s (0.55H, 2-H, E). Found, %:
C 72.01; H 5.11; N 7.75. C21H17ClN2O. Calculated, %:
C 72.31; H 4.91; N 8.03.
3
3
(1EZ,2E)-N-Benzyloxy-3-(4-bromophenyl)-1-
(pyridin-3-yl)prop-2-en-1-imine (5c). Yield 0.362 g
1
(1EZ,2E)-3-(4-Bromophenyl)-N-hexyloxy-1-
(pyridin-3-yl)prop-2-en-1-imine (5f). Yield 0.579 g
(74.9%), E/Z = 60:40, yellow oil. H NMR spectrum,
(46.0%), E/Z = 40:60, red–brown oil. H NMR spec-
trum, δ, ppm, (J, Hz): 5.16 s (1.20H, OCH2, Z), 5.29 s
(0.80H, OCH2, E), 6.33 d and 7.05 d (1.20H, CH=CH,
1
3
δ, ppm (J, Hz): 0.72–0.96 m (3H, CH3), 1.00–1.48 m
[6H, CH3(CH2)3], 1.50–1.83 m (2H, CH2CH2O), 4.05–
4.30 m (2H, CH2O), 6.44 d and 7.15 d (0.8H, CH=CH,
Z, J = 16.5), 6.65 d (0.4H, 3′-H, E, J = 16.1), 7.19–
7.50 m [9.60H, 2′-H (E), Harom), 7.58–7.72 m (1H,
5-H), 7.81 d (0.60H, 4-H, Z, J = 9.7), 8.05 d (0.40H,
4-H, E, J = 8.1), 8.55 s (0.40H, 2-H, Z), 8.67 d (1H,
6-H, J = 4.4), 8.73 s (0.60H, 2-H, E). Found, %:
C 64.06; H 4.40; N 7.10. C21H17BrN2O. Calculated, %:
C 63.83; H 4.56; N 6.89.
3
Z, J = 16.5), 6.76 d (0.60H, 2′-H, E, 3J = 16.9), 7.15–
7.66 m [5.60H, 2′-H (E), 5-H, Harom], 7.85 d (0.40H,
4-H, Z, J = 8.1), 8.20 d (0.60H, 4-H, E, J = 7.8), 8.55 s
(1H, 2-H), 8.66 d (1H, 6-H, J = 5.7). Found, %:
C 61.98; H 6.03; N 7.21. C20H23BrN2O. Calculated, %:
C 62.15; H 6.13; N 7.00.
(1EZ,2E)-3-(4-Fluorophenyl)-N-hexyloxy-
1-(pyridin-3-yl)prop-2-en-1-imine (5d). A solution of
0.454 g (2 mmol) of oxime 7a in 7 mL of anhydrous
DMF was cooled with an ice–salt bath, and 0.120 g
(3 mmol) of 60% sodium hydride was added under
argon. The mixture was stirred for 30 min, 0.34 mL
(2.5 mmol) of hexyl bromide was added, and the
mixture was stirred for 18 h at room temperature and
for 2.5 h at 60°C. The mixture was cooled, poured into
ice water (50 mL), and extracted with diethyl ether.
The extract was washed with 3 portions of water and
4 portions of 15% aqueous KOH, dried over Na2SO4,
and evaporated. The residue was purified by flash
chromatography on silica gel (5–40 μm) using first
methylene chloride (to remove DMF and hexene) and
then methylene chloride–ethyl acetate (gradient
elution). Yield 0.427 g (65.5%), E/Z = 80:20, yellow
(1EZ,2E)-N-Cyclohexyloxy-3-(4-fluorophenyl)-1-
(pyridin-3-yl)prop-2-en-1-imine (5g). Yield 0.088 g
(13.6%), E/Z = 45:55 (yellow oil). H NMR spectrum,
δ, ppm (J, Hz): 0.79–0.94 m and 1.13–1.68 m [10H,
(CH2)5], 4.05–4.29 m (1H, CHO), 6.36 d and 7.06 d
(1.10H, CH=CH, Z, 3J = 16.5), 6.68 d (0.45H, 2′-H, E,
J = 17.3), 7.14–7.74 m [6.00H, 2′-H (E), 4-H (Z), 5-H,
1
Harom), 7.80 d (0.45H, 4-H, E, J = 8.0), 8.57 s (1H,
2-H), 8.66 d (1H, 6-H, J = 4.0). Found, %: C 74.01;
H 6.56; N 8.62. C20H21FN2O. Calculated, %: C 73.98;
H 6.70; N 8.48.
(1EZ,2E)-3-(4-Chlorophenyl)-N-cyclohexyloxy-
1-(pyridin-3-yl)prop-2-en-1-imine (5h). Yield
0.215 g (31.5%), E/Z = 55:45, yellow oil. H NMR
spectrum, δ, ppm (J, Hz): 1.15–1.67 m and 1.71–
1.92 m [10H, (CH2)5], 4.10–4.30 m (1H, CHO), 6.36 d
and 7.05 d (0.90H, CH=CH, Z, J = 16.5), 6.67 d and
7.56 d (1.10H, CH=CH, E, J = 16.9), 7.27–7.42 m
(5H, 5-H, Harom), 7.83 d (0.45H, 4-H, Z, J = 7.7),
8.35 d (0.55H, 4-H, E, J = 8.0), 8.55 s (1H, 2-H), 8.58–
1
1
oil. H NMR spectrum, δ, ppm (J, Hz): 0.86 t (3H,
3
CH3, J = 6.9), 1.15–1.34 m [6H, CH3(CH2)3], 1.62 m
(2H, CH2CH2O), 4.04–4.30 m (2H, CH2O), 6.36 d
(0.20H, 3′-H, Z, J = 316.5), 6.67 d (0.80H, 3′-H, E, 3J =
16.1), 6.93–7.51 m (6H, FC6H4, 5-H, 2′-H), 7.64 d
3
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KUZENKOV, ZAKHARYCHEV
968
3. Sauter, H., Modern Crop Protection Compounds,
Krämer, W. and Schirmer, U., Eds., Weinheim: Wiley,
2007, vol. 2.
4. Wang, M., Qu, Zh., Du, D., and Jiang, L., Chin. J. Org.
Chem., 2013, vol. 33, p. 1005. doi 10.6023/
cjoc201212025
8.67 m (1H, 6-H). Found, %: C 70.45; H 6.25; N 8.20.
C20H21ClN2O. Calculated, %: C 70.12; H 6.44; N 8.01.
(1EZ,2E)-3-(4-Bromophenyl)-N-cyclohexyloxy-1-
(pyridin-3-yl)prop-2-en-1-imine (5i). Yield 0.149 g
1
(19.3%), E/Z = 15:85, yellow oil. H NMR spectrum,
δ, ppm (J, Hz): 1.21–1.72 m and 1.74–1.87 m [10H,
(CH2)5], 4.07–4.30 m (1H, CHO), 6.43 d and 7.15 d
(1.90H, CH=CH, Z, J = 16.5), 6.67 d (0.15H, 2′-H, E,
J = 16.9), 7.32–7.71 m [5.15H, 2′-H (E), 5-H, Harom],
7.77 d (0.85H, 4-H, Z, J = 7.7), 7.85 d (0.15H, 4-H, E,
J = 8.0), 8.52–8.71 m (1H, 6-H), 8.75 s (1H, 2-H).
Found, %: C 62.31; H 5.53; N 7.25. C20H21BrN2O.
Calculated, %: C 61.97; H 5.71; N 7.00.
5. Zan, N., Zhang, Yu., Zhang, Sh., Liu, S., and Jiang, L.,
Chin. J. Org. Chem., 2017, vol. 37, p. 2767. doi
10.6023/cjoc201705009
6. Zan, N., Wan, F., Wang, Sh., Zhang, J., and Jiang, L.,
Chin. J. Org. Chem., 2017, vol. 37, p. 1537. doi
10.6023/cjoc201701009
7. Martsynkevich, A.M., Zakharychev, V.V., and Shara-
nina, N.I., Russ. Chem. Bull., Int. Ed., 2011, vol. 60,
p. 521.
CONFLICT OF INTERESTS
8. Martsynkevich, A.M. and Zakharychev, V.V.,
Agrokhimiya, 2012, no. 3, p. 48.
The authors indicate the absence of conflict of
interests.
9. Kuzenkov, A.V. and Zakharychev, V.V., RU Patent
no. 2617413, 2017; Byull. Izobret., 2017, no. 12.
10. Zakharychev, V.V. and Kuzenkov, A.V., Chem.
Heterocycl. Compd., 2007, vol. 43, p. 989.
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 7 2019