Synthesis and biological activity of 3-substituted isoxazolecarboxamides

Article abstract of DOI:10.1007/s00706-010-0265-9

A series of novel 3-substituted isoxazolecarboxamides have been prepared. A key step was 1,3-dipolar cycloaddition of nitrile oxides to α,β-unsaturated esters. Some of these compounds exhibited high fungicidal activities against Alternaria alternata, Botrytis cinerea, Rhizoctonia solani, Fusarium culmorum, and Phytophthora cactorum.

Full text of DOI:10.1007/s00706-010-0265-9

Monatsh Chem (2010) 141:461–469
DOI 10.1007/s00706-010-0265-9
ORIGINAL PAPER
Synthesis and biological activity of 3-substituted
isoxazolecarboxamides
•
Mirosław Gucma W. Marek Gołe˛biewski
Received: 17 August 2009 / Accepted: 26 January 2010 / Published online: 23 February 2010
ꢀ Springer-Verlag 2010
Abstract A series of novel 3-substituted isoxazolecarb-
oxamides have been prepared. A key step was 1,3-dipolar
cycloaddition of nitrile oxides to a,b-unsaturated esters.
Some of these compounds exhibited high fungicidal
activities against Alternaria alternata, Botrytis cinerea,
Rhizoctonia solani, Fusarium culmorum, and Phytophthora
cactorum.
[3]. These results induced us to prepare a series of new
heterocyclic amide derivatives of 5- and 4-isoxazolecarb-
oxylic acids as potential protective plant agents.
Results and discussion
Synthesis of intermediates
Keywords Cycloaddition ꢀ Fungicides ꢀ Chlorination ꢀ
Regioselectivity
A key step in the synthesis was 1,3-dipolar cycloaddition of
nitrile oxides to a,b-unsaturated esters resulting in 2-isox-
azoline- or isoxazolecarboxylates, which were transformed
into amides via acid chlorides. Starting materials were
aldehydes, which were oximated with hydroxylamine and
chlorinated with N-chlorosuccinimide (NCS) in DMF to
form an imine group [4]. 4-Phenoxybenzaldehyde was
prepared in an Ullmann reaction of 4-bromobenzaldehyde
with phenol in DMF solution in the presence of anhydrous
pyridine [5]. The course of the reaction of aldoximes with
NCS depended on the solvent. In acetonitrile in the pres-
ence of half a molar equivalent of pyridine the major
products for substrates with electron-donating groups
(EDG) were nitriles, whereas benzaldoxime and oximes of
aliphatic aldehydes afforded starting aldehydes [6]. For the
majority of oximes chlorination with NCS in DMF pro-
ceeded smoothly, and nitrile oxides were generated in situ
in the presence of tertiary amines, usually triethylamine
(Huisgen method) [7] or on a basic Amberlyst A-21 col-
umn [8] (Scheme 1).
Introduction
Climatic changes and the quick appearance of resistance in
pathogenic organisms induce a continuous quest for new
protective plant agents that show selective activity against
pests and proper durability in the environment. The bio-
logical activity of carboxamides has been known for a long
time. Herbicidal potency results from inhibiting phytoenone
desaturase, an enzyme involved in the biosynthesis of
carotenoids [1]. Fungicidal activity of some phenyl amides
such as methalaxyl methyl originates from inhibition of
ribosomal RNA synthesis, and the activity of heteroaromatic
carboxamides, such as carboxine and thifluzamide, and
aromatic amides (mepronil) lies in the inhibition of succinic
dehydrogenase complex II from the pathogen respiration
chain [2]. However, simple derivatives of isoxazole show
also biological activity, e.g., hymexazole (3-hydroxy-5-
methylisoxazole), disturbs the RNA metabolism of fungi
Apart from the commercial ethyl acrylate, esters were
prepared by esterification of the corresponding acids or
transesterification of some esters. Methyl cinnamates
were synthesized from aryl aldehydes via Knoevenagel
condensation and acidic esterification. Reactions of mono-
substituted esters (acrylates) and a,a-disubstituted esters are
M. Gucma ꢀ W. M. Gołe˛biewski (&)
Institute of Industrial Organic Chemistry, Annopol 6,
03-236 Warsaw, Poland
e-mail: golebiewski@ipo.waw.pl
123

462
M. Gucma, W. M. Gołe˛biewski
OH
N
OH
N
of acid chlorides to 3-arylisoxazoles, 3-aryl-2-isoxazolines,
and aryl nitriles [11]. Efficiency of the acylation reaction
was much improved by formation of lithium amides with
n-butyl lithium in diethyl ether solution (method B) or with
t-butyl lithium (method C) reacting with acyl chlorides.
However, acylation in THF resulted mainly in formation of
n-butyl esters by cleavage of THF by butyl lithium. Four
types of amides (8–11) were prepared (Scheme 2).
The obtained amides were screened for herbicidal,
insecticidal, acaricidal and fungicidal activity. The best
activity was found against fungus isolates (Table 1). The
commercial fungicide chlorothalonil was tested as a refer-
ence compound under the same conditions as the isoxazole
carboxamides.
H
O
H
Cl
NH2OH
NCS
DMF
H2C CHCO2Et
Base
R1
R1
R1
1
2
3
O
O
O
CO2H
COCl
CO2Et
NaOH
N
N
N
(COCl)2
R1
R1
R1
5
4
6
O
O
N
N
H
H2N
R2
7
R2
Structure-activity relationship
R1
8
Amides with electron-donating groups (EDG) at the alde-
hyde-derived phenyl ring showed low fungicidal activity; a
smaller negative effect of EDGs at the other phenyl ring
was also observed. High biological activity was found for
compounds with electron-withdrawing groups (EWG) in
both aromatic functions, and was particularly outstanding
in case of CF3 and F substituted amides 8i, 9a, 9c, and 9f.
The last compound was more potent than the reference
pesticide chlorothalonil. An increase of activity with a
number of halide atoms in the first aromatic ring was found
(cf. 8e, 8h, 8i, and 9a); however, a second CF3 group
lowered the activity.
R
1 = Alkyl, OPh, OH, Cl, CF3
R2 = Alkyl, OMe, OCF3, Cl, Br, CF3, CN, NO2
Scheme 1
highly regioselective and afford 3-substituted-4,5-dihy-
droisoxazole-5-carboxylates. a,b-Disubstituted esters show
lower and opposite regiochemistry, and 4-substituted esters
are the major compounds. In an asymmetric version of the
reaction, we used chiral complexes of lanthanide triflates
with 2,20-binaphthol (BINOL) and obtained a series of 3-
aryl-2-isoxazolines with enantioselectivities up to 89% [9].
Regioselectivity of the reaction depended on the steric
demand of the ester group, and for t-butyl (E)-2-pentene-
carboxylate the 4-ester was the only product. The electronic
character of the dipole substituent was also important, since
reactions with dipoles bearing electron-donating substitu-
ents (4-i-Pr, 4-OMe) showed higher regioselectivity than
reactions with electron-withdrawing groups.
The substitution pattern was also crucial. Amides with a
CF3 group at position 4 and 3 were similarly active,
whereas 2-substituted products were devoid of activity.
The same trend was observed also for the other aromatic
ring. Introduction of another isoxazoline substituent (alkyl
or phenyl) at positions 4/5 was also detrimental (com-
pounds 10 and 11).
In conclusion, biological activity is influenced by a
combination of electronic and steric effects. High biolog-
ical activity can be correlated with low electron density of
the ring systems. Effective conjugation of the phenyl and
the isoxazole rings is also essential, and ortho substitution
in both rings is a detrimental factor causing the loss of
Synthesis of carboxamides
Some 3-aryl-4,5-dihydroisoxazolecarboxylates with halo-
and trifluoromethylaryl substituents were dehydrated to the
corresponding isoxazoles in a two-step reaction involving
NBS bromination and potassium acetate induced dehy-
drobromination [10]. Esters were saponified with aqueous-
ethanolic sodium hydroxide solution to carboxylic acids.
Acid chlorides were prepared by reaction of the carboxylic
acids with oxalyl chloride in benzene and further used to
acylate a series of aromatic, heteroaromatic, and aliphatic
amines typically in the presence of triethylamine (method
A). Yields were usually good; only in cases of weakly
nucleophilic aromatic amines with EWG were they modest,
and some side reactions took place because of degradation
O
O
O
R
N
N
N
N
H
N
R2
H
R2
O
R1
R1
9
R = Me; R1 = Cl; R2 = Br
11 R = 4-CF C H ; R1 = Pr; R2 = Br
R1 = F, CF3; R2 = Cl, F
10
i-
3
6 4
Scheme 2
123

Synthesis and biological activity of 3-substituted isoxazolecarboxamides
463
Table 1 Fungicidal inhibitory activities of compounds 8–11 at 200/20 lg cm-3
Comp.a
R1
R2
Alternaria
alternata
Botrytis
cinerea
Fusarium
culmorum
Phytophtora
cactorum
Rhizoctonia
solani
8aa
8ba
8ca
8da
4-OPh
4-Et
2,4,6-Cl3
2-CN
0
1
0
–
–
2
–
2
3
0
3
–
–
–
–
–
–
–
1
0
0
0
0
0
2
1
1
–
4-Et
4-CF3
1
0
0
0
2-OH
4-sec-Bu
4-Br
1
–
2
1
8e
2,4-Cl2
2,4-Cl2
2,3,6-Cl3
2,3,6-Cl3
4-CF3
2
1
1
1
8f
8ga
4-OMe
1
0
0
1
4-OCF3
1
0
1
1
8h
4-Br
2
2
2
2
8i
2,6-Cl2, 4-NO2
2,6-Cl2, 4-NO2
3,5-Cl2, 2,6-F2
3,5-Cl2, 2,6-F2
2,3,6-F3, 6-Cl
2,3,6-F3, 5-Cl
2,3,5,6-F4
2,3,5,6-F4
2,3,6-F3, 5-Cl
2,3,5,6-F4
4-Br
2
2
2
2
8j
3,5-(CF3)2
4-CF3
1
1
0
1
9a
9ba
2
3
2
3
4-CF3
2
1
2
–
9c
9da
4-CF3
3/2
2
2/1
2
3/2
3
3/1
1
2,4,5-F3
4-CF3
9e
2
2
2
2
9f
3-CF3
3/2
2
2/1
2
3/2
2
3/2
2
9g
3-CF3
9h
10a
11a
2-CF3
0
1
0
0
2,3,6-Cl3
4-i-Pr
0
1
1
0
4-Br
0
0
0
0
Chlorothalonil
2/2
1/0
2/1
3/2
At 0–3 scale: 0 = 0–20% growth inhibition; 1 = 21–50% growth inhibition; 2 = 51–80% growth inhibition; 3 = 81–100% growth inhibition
a
4,5-dihydroisoxazole derivative
coplanarity. Further studies are in progress to quantitatively
correlate electronic, steric, and hydrophobic effects with
fungicidal potency.
the corresponding aryl aldehyde oximes and NCS in DMF
[10]. The synthesis of compounds 4b, 4e, and 4g has
already been described [11].
General procedure for the cycloaddition reactions
Experimental
A solution of 13 mmol chloro-oxime in 15 cm3 anhydrous
toluene was added dropwise over 30 min to a stirred
mixture of anhydrous toluene, 6 cm3 anhydrous NEt3, 2 g
MgSO4, and 8 cm3 ethyl acrylate (80 mmol). The reaction
mixture was stirred overnight at room temperature, diluted
with 50 cm3 toluene, washed with water (5 9 100 cm3),
and evaporated in vacuo.
Reagent grade chemicals were used without further puri-
fication unless otherwise noted. Elemental analyses were
performed at the Microanalysis Laboratory of Institute of
Organic Chemistry, Polish Academy of Sciences, Warsaw.
Spectra were obtained as follows: IR spectra on JASCO
FTIR-420 spectrometer, 1H and 13C NMR spectra on
Varian 500 UNITY plus-500 and Varian 200 UNITY plus
200 spectrometers in deuterated chloroform using TMS as
internal standard, and EI mass spectra on AMD M-40. In
13C NMR spectra, signals of fluorine-substituted carbon
atoms and some a-carbons were not observed because of
strong 19F–13C coupling. In order to further characterize
these compounds, 19F spectra were recorded. Flash chro-
matography was carried out using silica gel S 230-400
mesh (Merck) and n-hexane-ethyl acetate mixtures as an
eluent. Hydroximinoyl acid chlorides were prepared from
General procedure for amide synthesis with tertiary
amines (method A)
A solution of an aniline derivative (1.2 mmol) in 10 cm3
anhydrous toluene was added with stirring to an acid
chloride followed by 4 cm3 dry triethylamine (30 mmol).
The solution was stirred under reflux for 1 h and overnight
at room temperature. Water (10 cm3) was added, and the
organic layer was washed with 3% hydrochloric acid
123

464
M. Gucma, W. M. Gołe˛biewski
Ethyl 3-(2,4-dichlorophenyl)isoxazole-5-carboxylate
(4d, C12H11Cl2NO3)
solution and water, and dried over magnesium sulfate. A
crude amide obtained after evaporation of the solvent was
purified by crystallization.
Yield 51%; m.p.: 154–157 ꢁC; 1H NMR (200 MHz,
CDCl3): d = 7.74 (d, J = 8.4 Hz, 1H, H-60), 7.45 (d,
J = 2.0 Hz, 1H, H-30), 7.42 (s, 1H, H-4), 7.38 (dd,
J = 8.4, 2.0 Hz, 1H, H-50), 4.47 (q, J = 7.2 Hz, 2H,
CH2), 1.44 (t, J = 7.2 Hz, 3H, CH3) ppm; IR (KBr):
m = 2,963, 2,920, 1,739, 1,584, 1,420, 1,307, 1,261, 1,215,
General procedure for amide synthesis with n-butyl
lithium (method B)
A 2.5-M solution of n-BuLi in hexane (0.2 cm3, 0.5 mmol)
was added dropwise at -78 ꢁC to a stirred solution of
4-aminopyridine derivative (0.4 mmol) in dry diethyl
ether. Stirring was continued for 1 h, and a solution of acid
chloride (0.3 mmol) in dry diethyl ether (or HMPA) was
added dropwise. The mixture was stirred for 5 h at 0 ꢁC
and overnight at room temperature. The reaction was
quenched with ammonium chloride solution, and the
product was extracted with methylene chloride and purified
by flash chromatography.
1,098, 803 cm-1
.
Methyl 4,5-dihydro-5-methyl-3-(2,3,6-trichlorophenyl)
isoxazole-4-carboxylate (4f, C12H10Cl3NO3)
Yield 60%; oil; 1H NMR (200 MHz, CDCl3): d = 7.49 (d,
J = 8.7 Hz, 1H, H-40), 7.34 (d, J = 8.7 Hz, 1H, H-50),
5.36 (quint, J = 6.7 Hz, 1H, H-5), 4.15 (d, J = 6.7 Hz,
1H, H-4), 3.64 (s, 3H, CH3O), 1.55 (d, J = 6.7 Hz, 3H,
CH3CH) ppm; IR (neat): m = 2,940, 1,743, 1,560, 1,440,
1,400, 1,210, 1,190, 1,110, 1,022, 920, 820, 780,
730 cm-1
.
General procedure for amide synthesis with t-butyl
lithium (method C)
Ethyl 3-[4-(trifluoromethyl)phenyl]isoxazole-5-carboxylate
(4h, C13H13F3NO3)
A 1.7-M solution of t-BuLi in hexane (1 cm3, 1.7 mmol)
was added dropwise at -78 ꢁC to a stirred solution of an
aniline derivative (1.2 mmol) in dry diethyl ether. Stirring
was continued for 1, h and a solution of acid chloride
(0.4 mmol) in dry HMPA was added dropwise. The mix-
ture was stirred for 4 h at 0 ꢁC and overnight at room
temperature. The reaction was quenched with ammonium
chloride solution, and the product was extracted with die-
thyl ether, washed with water, and purified by flash
chromatography.
Yield 89%; m.p.: 124–126 ꢁC; 1H NMR (CDCl3,
200 MHz): d = 7.97 (d, J = 8.4 Hz, 2H, H-30, H-50),
7.76 (d, J = 8.4 Hz, 2H, H-20, H-60), 7.29 (s, 1H, H-4),
4.48 (q, J = 7.0 Hz, 2H, CH2), 1.45 (t, J = 7.0 Hz, 3H,
CH3) ppm; IR (KBr): m = 3,124, 2,997, 2,925, 1,734,
1,438, 1,329, 1,165, 1,128, 1,071, 855, 767 cm-1; EIMS:
m/z (%) = 285 (M?, 18), 266 M?–F, 4), 212 (M?–CO2Et,
100), 184 (M?–CO2Et–C2H4, 18), 145 (C6H5CF3, 21).
Ethyl 3-[3,5-bis(trifluoromethyl)phenyl]isoxazole-5-
carboxylate (4i, C14H9F6NO3)
Ethyl 4,5-dihydro-3-(4-phenoxyphenyl)isoxazole-5-
carboxylate (4a, C18H17NO4)
1
Yield 73%; m.p.: 91–93 ꢁC; H NMR (200 MHz, CDCl3):
d = 8.30 (s, 2H, H-20, H-60), 8.00 (d, J = 0.6 Hz, 1H, H-
40), 7.36 (s, 1H, H-4), 4.49 (q, J = 7 Hz, 2H, OCH2), 1.46
(t, J = 7 Hz, 3H, CH3) ppm; IR (KBr): m = 3,132, 3,000,
1,722, 1,622, 1,444, 1,353, 1,284, 1,191, 1,145, 1,026, 953,
1
Yield 67%; oil; H NMR (200 MHz, CDCl3): d = 7.68–
7.62 (m, 2H, H-arom.), 7.42–7.31 (m, 2H, H-arom.), 7.20–
7.17 (m, 1H, H-arom.), 7.07–6.96 (m, 4H, H-arom.), 5.16
(dd, J = 10.4, 8.0 Hz, 1H, H-5), 4.27 (q, J = 7.1 Hz, 2H,
OCH2), 3.63 (d, J = 10.4 Hz, 1H, H-4a), 3.62 (d,
J = 8.0 Hz, 1H, H-4b), 1.33 (t, J = 7.2 Hz, 3H, CH3)
ppm.
914, 847, 834, 774, 707, 683 cm-1
.
Ethyl 4,5-dihydro-3-(2,4,5-trifluorophenyl)isoxazole-5-
carboxylate (4j, C12H10F3NO3)
Ethyl 4,5-dihydro-3-(2-hydroxyphenyl)isoxazole-5-
carboxylate (4c, C11H13NO4)
Yield 70%; oil; 1H NMR (200 MHz, CDCl3): d = 7.76 (m,
J = 8.7 Hz, 1H, H-60), 7.00 (td, J = 10.0, 6.5 Hz, 1H,
H-30), 5.18 (dd, J = 9.4, 9.1 Hz, 1H, H-5), 4.28 (q,
J = 7.2 Hz, 2H, OCH2CH3), 3.70 (d, J = 9.1 Hz, 2H,
H-4a), 3.68 (d, J = 9.4 Hz, 1H, H-4b), 1.33 (t, J = 7.2 Hz,
3H, CH3CH2) ppm; IR (neat): m = 3,080, 2,986, 1,741,
1,690, 1,627, 1,580, 1,512, 1,480, 1,440, 1,367, 1,285,
1
Yield 64%; oil; H NMR (200 MHz, CDCl3): d = 9.56
(1H, OH), 7.39–7.11 (m, 2H, H-40, H-60), 7.04 (dd,
J = 8.4, 1.0 Hz, 1H, H-30), 6.93 (m, 1H, H-50), 5.14 (dd,
J = 10.2, 8.0 Hz, 1H, H-5), 4.28 (q, J = 7.2 Hz, 2H,
CH2), 3.74 (d, J = 10.2 Hz, 1H, H-4a), 3.73 (d,
J = 8.0 Hz, 1H, H-4b), 1.33 (t, J = 7.2 Hz, 3H,
CH3CH2O) ppm; HRMS: calcd for C12H13NNaO4
[M ? Na?] 258.0742, found 258.0751.
1,208, 1,162, 1,140, 1,035, 1,011, 891, 850, 809, 730 cm-1
;
HRMS: calcd for C12H10F3NNaO3 [M ? Na?] 296.0505,
found 296.0513.
123

Synthesis and biological activity of 3-substituted isoxazolecarboxamides
465
Ethyl 3-[3-(trifluoromethyl)phenyl]isoxazole-5-carboxylate
(4k, C13H13F3NO3)
(d, J = 8.4 Hz, 2H, H-20, H-60), 7.29 (s, 1H, H-4), 2.68 (q,
J = 7.0 Hz, 2H, CH2), 1.45 (t, J = 7.0 Hz, 3H, CH3) ppm;
13C NMR (50.3 MHz, CDCl3): d = 175.0, 156.7, 147.7,
128.6 (2C), 127.3 (2C), 125.6, 77.4, 29.0, 15.5 ppm; IR
(KBr): m = 3,500–2,800, 1,730 (COOH) cm-1; EIMS: m/z
(%) = 285 (M?, 18), 266 (M?–F, 4), 212 (M?–CO2Et,
100), 184 (M?–CO2Et–C2H4, 18), 145 (C6H5CF3, 21).
Yield 82%; oil; 1H NMR (200 MHz, CDCl3): d = 8.09 (s,
1H, H-20), 8.04 (d, J = 7.7 Hz, 1H, H-40), 7.75 (d,
J = 7.7 Hz, 1H, H-60), 7.63 (t, J = 7.7 Hz, 1H, H-50),
7.31 (s, 1H, H-4), 4.48 (q, J = 7.1 Hz, 2H, CH2CH3), 1.45
(t, J = 7.1 Hz, 3H, CH2CH3) ppm; IR (neat): m = 3,448,
3,120, 2,940, 2,910, 1,731, 1,620, 1,583, 1,470, 1,450,
1,390, 1,369, 1,335, 1,307, 1,227, 1,168, 1,120, 1,077,
4,5-Dihydro-3-(2-hydroxyphenyl)isoxazole-5-carboxylic
acid (5c, C10H9NO4)
1,017, 940, 912, 860, 809, 772, 697 cm-1
.
1
Yield 61%; m.p.: 80–82 ꢁC; H NMR (200 MHz, CDCl3):
Ethyl 3-[2-(trifluoromethyl)phenyl]isoxazole-5-carboxylate
(4l, C13H13F3NO3)
d = 9.45 (s, 1H, COOH), 8.36 (s, 1H, ArOH), 7.15 (m, 4H,
H-30, H-40, H-50, H-60), 5.23 (m, 1H, H-5), 3.78 (dd,
J = 9.2, 8.2 Hz, 1H, H-4), 3.78 (m, 1H, H-4) ppm; IR
(KBr): m = 3,410, 3,051, 2,680, 2,530, 1,721, 1,620, 1,598,
1,575, 1,493, 1,475, 1,438, 1,398, 1,360, 1,310, 1,259,
Yield 96%; oil; 1H NMR (200 MHz, CDCl3): d = 7.82 (m,
1H, H-60), 7.68–7.57 (m, 3H, H-40, H-50, H-60), 7.14 (s, 1H,
H-4), 4.47 (q, J = 7.2 Hz, 2H, CH2CH3), 1.44 (t,
J = 7.2 Hz, 3H, CH2CH3) ppm; 13C NMR (50.3 MHz,
CDCl3): d = 162.8, 160.6, 156.8, 132.3, 132.3, 132.0,
130.4, 129.0 (q, J = 31.4 Hz), 126.7 (q, J = 5.2 Hz),
110.6 (q, J = 3.2 Hz) ppm; IR (neat): m = 2,987, 2,920,
1,740, 1,610, 1,581, 1,520, 1,470, 1,434, 1,390, 1,370,
1,316, 1,290, 1,275, 1,221, 1,180, 1,134, 1,080, 1,050,
1,035, 1,020, 950, 930, 770, 693 cm-1; HRMS: calcd for
C13H13F3NNaO3 [M ? Na?] 308.0505, found 308.0596.
1,240, 1,220, 1,160, 1,100, 980, 921, 878, 823, 750 cm-1
.
3-(2,4-Dichlorophenyl)isoxazole-5-carboxylic acid
(5d, C10H5Cl2NO3)
Yield 92%; m.p.: 165–167 ꢁC; 1H NMR (200 MHz,
CDCl3): d = 7.76 (d, J = 8.2 Hz, 1H, H-60), 7.56 (d,
J = 2.0 Hz, 1H, H-30), 7.52 (s, 1H, H-4), 7.39 (dd,
J = 8.2, 2.0 Hz, 1H, H-50) ppm; EIMS: m/z (%) = 257
(M?, 32), 212 (M?–CO2H, 100), 184 (M?–CO2H–CO,
44).
Ethyl 4,5-dihydro-3-(4-isopropylphenyl)-5-
[4-(trifluoromethyl)phenyl]isoxazole-4-carboxylate
(4m, C22H22F3NO3)
4,5-Dihydro-3-(2,3,6-trichlorophenyl)isoxazole-5-
carboxylic acid (5e, C12H6Cl3NO3)
Yield 84%; oil; 1H NMR (200 MHz, CDCl3): d = 7.66 (d,
J = 7.6 Hz, 2H, H-60, H-20), 7.65 (d, J = 8.3 Hz, 2H,
H-300, H-500), 7.51 (d, J = 7.6 Hz, 2H, H-200, H-600), 7.26
(d, J = 8.3 Hz, 2H, H-30, H-50), 6.02 (d, J = 6.1 Hz, 1H,
H-5), 4.39 (d, J = 6.1 Hz, 1H, H-4), 4.26 (q, J = 7.1 Hz,
2H, OCH2), 2.93 (m, J = 7.1 Hz, 1H, CH[CH3]2), 1.25
(d, J = 7.0 Hz, 6H, CH[CH3]2), 1.08 (t, J = 7.1 Hz, 3H,
CH3CH2O) ppm.
1
Yield 87%; m.p.: 89–91 ꢁC; H NMR (CDCl3, 200 MHz):
d = 7.50 (d, J = 8.6 Hz, 1H, H-40), 7.34 (d, J = 8.6 Hz,
1H, H-50), 5.33 (dd, J = 11.2, 6.8 Hz, 1H, H-5), 4.30 (q,
J = 7.2 Hz, 2H, CH2), 3.66 (d, J = 11.2 Hz, 1H, H-4),
3.62 (d, J = 6.8 Hz, 1H, H-4) ppm; 13C NMR (50.3 MHz,
CDCl3): d = 173.6, 154.2, 133.6, 133.3, 132.5, 132.2,
129.2, 128.9, 72.0, 41.3 ppm; IR (KBr): m = 3,600–2,500,
1,731 (COOH), 819, 523 cm-1
.
4,5-Dihydro-3-(4-phenoxyphenyl)isoxazole-5-carboxylic
acid (5a, C16H13NO4)
3-[4-(Trifluoromethyl)phenyl]isoxazole-5-carboxylic
acid (5f, C11H6F3NO3)
1
Yield 71%; glass; H NMR (200 MHz, CDCl3): d = 7.63
Yield 71%; m.p.: 192–195 ꢁC; 1H NMR (200 MHz,
CDCl3): d = 7.99 (d, J = 8.1 Hz, 2H, H-30, H-50), 7.77
(d, J = 8.1 Hz, 2H, H-20, H-60), 7.38 (s, 1H, H-4) ppm; IR
(KBr): m = 3,400–2,900, 2,923, 1,720, 1,328, 1,136, 1,071,
(dd, J = 8.8, 2.0 Hz, 2H, H-200, H-600), 7.35 (dd, J = 8.8,
7.9 Hz, 2H, H-300, H-500), 7.12 (t, J = 7.9 Hz, 1H, H-400),
7.05 (d, J = 8.0 Hz, 2H, H-20, H-60), 6.99 (d, J = 8.0 Hz,
2H, H-30, H-50), 6.45 (s, 1H, HO), 5.23 (dd, J = 8.3,
9.2 Hz, 1H, H-5), 3.73 (d, J = 8.3 Hz, 1H, H-4), 3.69 (d,
J = 9.2 Hz, 1H, H-4) ppm; IR (KBr): m = 3,432, 3,050,
2,940, 1,726, 1,589, 1,510, 1,490, 1,358, 1,250, 1,165,
1,094, 1,005, 875, 830, 752, 693 cm-1; EIMS: m/z
(%) = 281 (M?, 75), 236 (M?–HOC=O, 70), 77 (C6H5,
100).
842 cm-1
.
3-[3,5-Bis(trifluoromethyl)phenyl]isoxazole-5-carboxylic
acid (5g, C12H5F6NO3)
Yield 83%; m.p.: 152–154 ꢁC; 1H NMR (500 MHz,
CDCl3): d = 8.32 (s, 2H, H-60, H-20), 8.02 (s, 1H, H-40),
7.48 (s, 1H, H-4), 5.48 (s, OH) ppm; 13C NMR (50.3 MHz,
CDCl3): d = 161.1, 159.1, 146.9, 132.9 (q, J = 34.2 Hz,
2C), 130.0, 127.0 (m), 124.3 (m), 108.4 ppm; 19F NMR
(471 MHz, CDCl3): d = -63.5 ppm; IR (KBr): m = 3,429,
3,170, 2,980, 2,670, 1,720, 1,615, 1,605, 1,590, 1,500,
3-(4-Ethylphenyl)-4,5-dihydroisoxazole-5-carboxylic
acid (5b, C12H13NO3)
Yield 89%; m.p.: 106–108 ꢁC; 1H NMR (200 MHz,
CDCl3): d = 7.97 (d, J = 8.4 Hz, 2H, H-30, H-50), 7.76
123

466
M. Gucma, W. M. Gołe˛biewski
1,450, 1,422, 1,354, 1,282, 1,170, 1,143, 1,075, 990, 902,
846, 799, 760, 730, 706, 683 cm-1
4,5-Dihydro-3-(4-isopropylphenyl)-5-[4-(trifluoro-
methyl)phenyl]isoxazole-4-carboxylic acid
(5l, C20H18F3NO3)
.
4,5-Dihydro-3-(2,4,5-trifluorophenyl)isoxazole-5-
carboxylic acid (5h, C10H6F3NO3)
Yield 94%; glass; IR (KBr): m = 2,960, 1,717, 1,610,
1,415, 1,323, 1,265, 1,160, 1,130, 1,069, 1,018, 960, 894,
836 cm-1; EIMS: m/z (%) = 377 (M?, 26), 362 (M?–
CH3, 20), 334 (M?–CH[CH3]2, 12), 333 (M?–O=C–O, 58),
318 (M?–O=C–OCH2, 25), 303 (M?–O=C–O[CH3]2, 12),
188 (M?–O=C–OC6H4CF3, 18), 173 (M?–O=C–
OC6H4CF3CH3, 31), 145 (C6H4CF3, 28), 43 (CH[CH3]2,
71).
1
Yield 75%; m.p.: 90–93 ꢁC; H NMR (200 MHz, CDCl3):
d = 7.75 (dt, J = 10.0, 6.5 Hz, 1H, H-60), 7.01 (td,
J = 10.0, 6.5 Hz, 1H, H-30), 6.51 (s, 1H, OH), 5.25 (dd,
J = 10.5, 7.9 Hz, 1H, H-5), 3.76 (d, J = 10.5 Hz, 2H,
H-4a), 3.74 (d, J = 7.9 Hz, 1H, H-4b) ppm; 13C NMR
(50.3 MHz, CDCl3): d = 174.3, 151.7, 116.7 (dd,
J = 24.2, 3.6 Hz), 114.8 (dd, J = 21.7, 4.3 Hz), 77.8,
40.3 (d, J = 8.3 Hz) ppm; IR (KBr): m = 3,433, 3,080,
2,920, 2,650, 1,719, 1,628, 1,580, 1,516, 1,440, 1,367,
1,290, 1,230, 1,190, 1,140, 1,010, 980, 897, 806, 730, 645,
4,5-Dihydro-3-(4-phenoxyphenyl)isoxazole-5-
carboxylic acid 2,4,6-trichlorophenylamide
(8a, C22H15Cl3N2O3)
600 cm-1
.
Method A, yield 41%; m.p.: 254–257 ꢁC; 1H NMR
(200 MHz, CDCl3): d = 8.90–7.00 (m, 12H, H-30, H-50,
H-20, H-60, H-300, H-500, H-200, H-600, H-400, H-3¢¢¢, H-5¢¢¢,
NH), 5.33 (dd, J = 9.0, 8.1 Hz, 1H, H-5), 3.78 (d,
J = 9.0 Hz, 1H, H-4), 3.77 (d, J = 8.1 Hz, 1H, H-4)
ppm; 13C NMR (50.3 MHz, CDCl3): d = 169.1, 159.5,
158.8, 155.2, 135.3 (2C), 134.9, 129.9 (2C), 129.7 (2C),
129.1 (2C), 125.3, 124.7, 122.5, 120.5 (2C), 118.7 (2C),
76.6, 39.8 ppm; IR (KBr): m = 3,434, 3,262, 3,080, 1,693,
1,580, 1,555, 1,487, 1,373, 1,243, 1,167, 1,078, 847, 804,
690 cm-1; EIMS: m/z (%) = 462 (M?, 2), 238 (M?–
CONHC6H2Cl3, 5), 224 (OCNHC6H2Cl3, 10), 195
(NHC6H2Cl3, 45), 169 (C6H5OC6H4, 20).
3-[3-(Trifluoromethyl)phenyl]isoxazole-5-carboxylic
acid (5i, C11H6F3NO3)
Yield 88%; m.p.: 104–106 ꢁC; 1H NMR (200 MHz,
CDCl3): d = 8.04 (s, 1H, OH), 8.12 (s, 1H, H-20), 8.04
(d, J = 7.6 Hz, 1H, H-40), 7.77 (d, J = 7.6 Hz, 1H, H-60),
7.65 (t, J = 7.6 Hz, 1H, H-50), 7.43 (s, 1H, H-4) ppm; 13C
NMR (50.3 MHz, CDCl3): d = 170.9, 162.1, 160.6, 130.1,
129.8, 129.7 (q, J = 39.6 Hz), 128.6, 127.4 (q,
J = 3.5 Hz), 123.8 (q, J = 3.6 Hz), 108.6 ppm; IR
(KBr): m = 3,440, 3,120, 2,910, 1,730, 1,698, 1,620,
1,600, 1,585, 1,457, 1,430, 1,410, 1,380, 1,329, 1,280,
1,230, 1,180, 1,150, 1,128, 1,100, 1,071, 990, 940, 915,
3-(4-Ethylphenyl)-4,5-dihydroisoxazole-5-carboxylic
acid 2-cyanophenylamide (8b, C19H17N3O2)
860, 805, 780, 760, 698 cm-1
.
Method A, yield 25%; glass; 1H NMR (200 MHz, CDCl3):
d = 9.12 (s, 1H, NH), 8.31 (d, J = 8.2 Hz, 1H, H-300), 7.63
(d, J = 8.3 Hz, 2H, H-60, H-20), 7.62 (d, 1H, J = 7.8 Hz,
H-600), 7.58 (dd, J = 7.8, 1.6 Hz, 1H, H-500), 7.26 (d,
J = 8.3 Hz, 2H, H-50, H-30), 7.26–7.19 (td, J = 8.4,
1.4 Hz, 1H, H-400), 5.29 (dd, J = 9.7, 6.7 Hz, 1H, H-5),
3.79 (m, J = 9.8, 6.4 Hz, 2H, H-4), 2.68 (q, J = 7.6 Hz,
2H, CH2), 1.24 (t, J = 7.4 Hz, 3H, CH3) ppm; 13C NMR
(50.3 MHz, CDCl3): d = 170.2, 157.6, 147.7, 139.2,
134.1, 132.7, 128.5 (2C), 127.3 (2C), 125.5, 125.2, 121.8,
115.9, 103.9, 78.9, 40.0, 28.9, 15.4 ppm; IR (KBr):
m = 3,366, 1,698, 1,581, 1,523, 1,449, 1,303, 860, 829,
759 cm-1; EIMS: m/z (%) = 319 (M?, 7), 174 (M?–
CONHC6H4CN, 100), 118 (NH2C6H4CN, 25), 105
(C6H4C2H5, 10).
3-[2-(Trifluoromethyl)phenyl]isoxazole-5-carboxylic
acid (5j, C11H6F3NO3)
1
Yield 78%; glass; H NMR (200 MHz, CDCl3): d = 9.81
(s, 1H, OH), 7.82 (m, 1H, H-30), 7.68–7.58 (m, 3H, H-40,
H-50, H-60), 7.67 (s, 1H, H-4) ppm; 13C NMR (50.3 MHz,
CDCl3): d = 162.4, 160.3, 159.9, 132.4, 132.4, 132.0,
130.6, 129.0 (q, J = 31.4 Hz), 126.8 (q, J = 5.2 Hz),
112.0 (q, J = 3.2 Hz) ppm; IR (KBr): m = 3,000, 2,840,
1,717, 1,605, 1,595, 1,580, 1,515, 1,445, 1,400, 1,387,
1,315, 1,270, 1,232, 1,180, 1,126, 1,105, 990, 950, 938,
905, 850, 771, 690 cm-1
.
4,5-Dihydro-5-methyl-3-(2,3,6-trichlorophenyl)isoxazole-
4-carboxylic acid (5k, C11H8Cl3NO3)
Obtained by hydrolysis of a corresponding known ester [9].
1
Yield 67%; glass; H NMR (200 MHz, CDCl3): d = 8.40
(s, 1H, OH), 7.49 (d, J = 8.8 Hz, 1H, H-40), 7.33 (d,
J = 8.8 Hz, 1H, H-50), 5.30 (quint, J = 6.7 Hz, 1H, H-5),
4.21 (d, J = 6.7 Hz, 1H, H-4), 1.55 (d, J = 6.7 Hz, 3H,
CH3CH) ppm; IR (neat): m = 3,420, 3,080, 2,986, 2,640,
1,715, 1,635, 1,422, 1,388, 1,287, 1,230, 1,200, 1,180,
3-(4-Ethylphenyl)isoxazole-5-carboxylic acid
(4-trifluoromethyl)phenylamide (8c, C19H15F3N2O2)
Method A, yield 95%; m.p.: 154–156 ꢁC; 1H NMR
(200 MHz, CDCl3): d = 8.70 (s, 1H, NH), 7.72
(d, J = 8.8 Hz, 2H, H-300, H-500), 7.60 (d, J = 8.4 Hz,
2H, H-20, H-60), 7.59 (d, 2H, J = 8.8 Hz, H-200), 7.26
1,036, 917, 830, 818, 760, 720 cm-1
.
123

Synthesis and biological activity of 3-substituted isoxazolecarboxamides
467
(d, J = 8.4 Hz, H-30, H-50), 5.25 (dd, J = 10.2, 6.6 Hz,
1H, H-5), 3.80 (d, J = 6.6 Hz, 1H, H-4a), 3.78 (d,
J = 10.2 Hz, 1H, H-4b), 2.85 (q, J = 7.6 Hz, 2H, CH2Ph),
1.24 (t, J = 7.6 Hz, 3H, C–CH3) ppm; 13C NMR
(50.3 MHz, CDCl3): d = 169.6, 157.0, 148.4, 145.5,
129.6 (2C), 128.4 (2C), 127.3 (q, J = 4.0 Hz, 2C), 121.7,
121.3 (2C), 80.6, 40.4, 29.5, 16.3 ppm; IR (KBr):
m = 3,320, 2,962, 2,925, 1,681, 1,620, 1,530, 1,411,
4,5-Dihydro-3-(2,3,6-trichlorophenyl)isoxazole-5-
carboxylic acid 4-(trifluoromethoxy)phenylamide
(8g, C17H10Cl3F3N2O3)
Method B, yield 37%; glass; 1H NMR (200 MHz, CDCl3):
d = 8.60 (s, 1H, NH), 7.63 (d, J = 8.8 Hz, 1H, H-600), 7.51
(d, J = 8.8 Hz, 1H, H-40), 7.34 (d, J = 8.8 Hz, 1H, H-30),
7.22 (d, J = 8.8 Hz, 2H, H-300, H-500), 5.35 (dd, J = 10.8,
5.4 Hz, 1H, H-5), 3.74 (d, J = 10.8 Hz, 1H, H-4), 3.69 (d,
J = 5.4 Hz, 1H, H-4) ppm; 13C NMR (50.3 MHz, CDCl3):
d = 167.9, 158.1, 151.3 (q, J = 4.8 Hz), 139.9, 134.1,
133.8, 133.6, 132.5, 132.4, 129.0, 122.5 (2C), 121.3 (2C),
78.9, 38.4 ppm; IR (KBr): m = 3,300, 3,080, 2,932, 1,684,
1,610, 1,530, 1,510, 1,450, 1,420, 1,305, 1,262, 1,220,
1,165, 1,107, 1,040, 850, 817, 750 cm-1; EIMS: m/z
(%) = 477 (M?, 65).
1,327, 1,160, 1,123, 1,072, 836 cm-1
.
4,5-Dihydro-3-(2-hydroxyphenyl)isoxazole-5-carboxylic
acid 4-(sec-butyl)phenylamide (8d, C20H22N2O3)
Method A, yield 55%; glass; 1H NMR (200 MHz, CDCl3):
d = 9.47 (s, 1H, NH), 8.41(s, 1H, HO), 7.48 (d,
J = 8.6 Hz, 2H, H-600, H-200), 7.16 (m, 4H, H-30, H-40,
H-50, H-60), 7.15 (d, J = 8.6 Hz, 2H, H-300, H-500), 5.23 (dd,
J = 11.2, 5.6 Hz, 1H, H-5), 3.90 (d, J = 5.6 Hz, 1H, H-4),
3.86 (d, J = 11.2 Hz, 1H, H-4), 2.57 (m, 1H, CH), 1.56 (m,
2H, CH2), 1.20 (d, J = 5.6 Hz, 3H, CH3), 0.79 (t,
J = 7.4 Hz, 3H, CH3) ppm; 13C NMR (50.3 MHz,
CDCl3): d = 168.4, 159.6, 157.6, 144.9, 134.4, 132.8,
129.2, 127.8 (2C), 120.3 (2C), 120.1, 117.3, 113.0, 77.9,
41.4, 40.2, 31.3, 22.0, 12.4 ppm; IR (KBr): m = 3,300,
3,060, 2,961, 1,683, 1,600, 1,525, 1,495, 1,417, 1,310,
3-(2,3,6-Trichlorophenyl)isoxazole-5-carboxylic acid
4-bromophenylamide (8h, C16H8BrCl3N2O2)
Method A, yield 39%; glass; 1H NMR (200 MHz, CDCl3):
d = 8.38 (s, 1H, NH), 7.59 (d, J = 8.6 Hz, 2H, H-200,
H-600), 7.51 (d, J = 8.7 Hz, 1H, H-40), 7.45 (d, J = 8.7 Hz,
1H, H-50), 7.40 (d, J = 8.6 Hz, 2H, H-300, H-500), 7.12 (s,
1H, H-4) ppm; 13C NMR (50.3 MHz, CDCl3): d = 163.5,
160.2, 153.2, 135.5, 134.0, 133.6, 132.6, 132.3, 132.2 (3C),
128.8, 121.9 (2C), 118.4, 109.4 ppm; IR (KBr): m = 3,341,
3,292, 3,110, 2,920, 1,695, 1,663, 1,620, 1,590, 1,539,
1,490, 1,420, 1,395, 1,350, 1,313, 1,250, 1,181, 1,099,
1,258, 918, 870, 824, 754 cm-1
.
3-(2,4-Dichlorophenyl)isoxazole-5-carboxylic acid
4-bromophenylamide (8e, C16H9BrCl2N2O2)
1,073, 1,009, 880, 820, 759 cm-1
.
Method A, yield 75%; glass; 1H NMR (CDCl3, 200 MHz):
d = 8.26 (s, 1H, NH), 7.72 (d, J = 8.2 Hz, 1H, H-60), 7.56
(m, 4H, H-200, H-300, H-500, H-600), 7.49 (s, 1H, H-4), 7.39
(dd, J = 8.2, 1.9 Hz, 1H, H-50) ppm; 13C NMR
(50.3 MHz, CDCl3): d = 163.2, 161.8, 153.6, 137.4,
135.8, 134.1, 132.6 (2C), 131.9, 131.0, 130.8, 128.0,
122.1 (2C), 109.2 ppm; IR (KBr): m = 3,340, 2,340, 1,670,
1,596, 1,532, 1,395, 819 cm-1; EIMS: m/z (%) = 410
(M?, 27), 214 (M?–O=C–NHC6H4Br, 68), 172
(NH2C6H4Br, 15), 171 (NHC6H4Br, 7), 157 (C6H4Br,
16), 75 (C6H3, 16).
3-[4-(Trifluoromethyl)phenyl]isoxazole-5-carboxylic acid
2,6-dichloro-4-nitrophenylamide (8i, C17H8Cl2F3N3O4)
Method C, yield 49%; m.p.: 129–131 ꢁC; 1H NMR
(200 MHz, CDCl3): d = 8.39 (s, 1H, NH), 8.17 (s, 2H,
H-300, H-500), 7.92 (d, J = 8.2 Hz, 2H, H-30, H-50), 7.75 (d,
J = 8.2 Hz, 2H, H-20, H-60), 7.47 (s, 1H, H-4) ppm; 13C
NMR (50.3 MHz, CDCl3): d = 162.6, 161.7, 152.3, 144.5,
142.1, 136.4 (2C), 128.9, 127.6 (2C), 126.6 (2C), 126.1 (2C,
q, J = 3.9 Hz), 107.9 ppm; IR (KBr): m = 3,364, 1,700,
1,623, 1,496, 1,325, 1,131, 1,065, 950, 900, 816, 741 cm-1
;
EIMS: m/z (%) = 446 (M?, 1), 410 (M?–Cl, 35), 240 (M?–
NHC6H2Cl2NO2, 63), 212 (M?–NHC6H2Cl2NO2C=O,
100), 145 (C6H5CF3, 51), 69 (CF3, 10).
3-(2,4-Dichlorophenyl)isoxazole-5-carboxylic acid
4-methoxyphenylamide (8f, C17H12Cl2N2O3)
Method A, yield 69%; m.p.: 154–157 ꢁC; 1H NMR
(200 MHz, CDCl3): d = 8.39 (s, 1H, NH), 7.71 (d,
J = 8.6 Hz, 1H, H-60), 7.57 (d, J = 8.8 Hz, 2H, H-200,
H-600), 7.47 (d, J = 2.0 Hz, 1H, H-30), 7.46 (s, 1H, H-4),
7.30 (dd, J = 8.6, 2.0 Hz, 1H, H-50), 3.80 (s, 3H, OCH3)
ppm; 13C NMR (50.3 MHz, CDCl3): d = 163.7, 161.7,
157.6, 153.5, 137.3, 134.1, 131.9, 130.7, 129.8, 127.9,
126.0, 122.3 (2C), 114.7 (2C), 108.8, 55.7 ppm; IR (KBr):
m = 3,382, 2,922, 1,684, 1,540, 1,510, 1,423, 1,250, 1,034,
3-[3,5-Bis(trifluoromethyl)phenyl]isoxazole-5-carboxylic
acid 2,6-dichloro-4-nitrophenylamide
(8j, C18H7Cl2F6N3O4)
Method C, yield 31%; glass; 1H NMR (200 MHz, CDCl3):
d = 8.35 (s, 2H, H-500, H-300), 8.32 (s, 2H, H-20, H-60), 8.21
(s, 1H, NH), 8.04 (s, 1H, H-40), 7.52 (s, 1H, H-4) ppm; 13C
NMR (50.3 MHz, CDCl3): d = 162.1, 159.6, 152.2, 144.7,
142.0, 136.3 (2C), 129.4, 128.3 (2C, q, J = 4.3 Hz),
107.2 ppm; IR (KBr): m = 3,438, 3,100, 1,689, 1,630,
1,541, 1,520, 1,352, 1,281, 1,185, 1,137, 904, 815, 740,
825 cm-1
;
EIMS: m/z (%) = 362 (M?, 53), 212
(M?–C8H8NO2, 100), 184 (M?–C8H8NO2–CO, 27), 149
(M?–C8H8NO2–CO–Cl, 34), 123 (C4H3Cl2, 85).
706 cm-1
.
123

468
M. Gucma, W. M. Gołe˛biewski
3-[4-(Trifluoromethyl)phenyl]isoxazole-5-carboxylic acid
3,5-dichloro-2,6-difluoropyridin-4-ylamide
(9a, C16H6Cl2F5N3O2)
-72.9 (dd, J = 26.4, 13.2 Hz, 1F), -86.8 (dd, J = 21,7,
13.2 Hz, 1F), -113.4 (m, 1F), -127.3 (dtd, J = 22.2, 8.5,
5.7 Hz, 1F), -140.5 (m, 1F), -141.8 (dd, J = 26.4,
20.7 Hz, 1F) ppm; IR (KBr): m = 3,380, 3,253, 3,120,
3,020, 2,900, 1,701, 1,624, 1,580, 1,520, 1,477, 1,440,
1,400, 1,360, 1,270, 1,240, 1,193, 1,140, 1,095, 1,073,
1
Yield 51%; glass; H NMR (200 MHz, CDCl3): d = 8.32
(s, 1H, NH), 8.0 (d, J = 8.2 Hz, 2H, H-50, H-30), 7.80 (d,
J = 8.2 Hz, 2H, H-60, H-20), 7.50 (s, 1H, H-4) ppm; 13C
NMR (50.3 MHz, CDCl3): d = 162.5, 161.7, 152.6, 128.9,
127.4 (2C), 126.4 (2C, t, J = 3.9 Hz), 107.6 ppm; 19F
NMR (471 MHz, CDCl3): d = -63.4 (s, 3F), -69.3 (s,
2F) ppm; IR (KBr): m = 3,240, 3,000, 1,695, 1,603, 1,501,
1,435, 1,411, 1,326, 1,280, 1,160, 1,138, 1,073, 1,020, 952,
1,030, 1,005, 925, 895, 875, 800, 730 cm-1
.
3-[4-(Trifluoromethyl)phenyl]isoxazole-5-carboxylic acid
2,3,5,6-tetrafluoropyridin-4-ylamide (9e, C16H6F7N3O2)
Method C, yield 66%; m.p.: 209–211 ꢁC, 1H NMR
(200 MHz, (CD3)2CO): d = 8.32 (s, 1H, NH), 8.00 (d,
J = 8.3 Hz, 2H, H-30, H-50), 7.80 (d, J = 8.3 Hz, 2H, H-
20, H-60), 7.50 (s, 1H, H-4) ppm; 13C NMR (50.3 MHz,
(CD3)2CO): d = 163.5, 162.5, 154.1, 132.1, 127.9 (2C),
126.3 (2C, q, J = 4.0 Hz), 106.7 ppm; 19F NMR
(471 MHz, (CD3)2CO): d = -63.9 (3F), -93.1 (m, 1F),
-141.5 (m, 1F), -146.1 (m, 1F), -146.5 (m, 1F) ppm; IR
(KBr): m = 3,450, 3,297, 3,130, 2,920, 2,840, 1,698, 1,650,
1,620, 1,522, 1,490, 1,436, 1,420, 1,328, 1,285, 1,240,
1,171, 1,131, 1,118, 1,077, 1,050, 1,000, 960, 910, 870,
891, 849, 788, 739 cm-1
.
4,5-Dihydro-3-[4-(trifluoromethyl)phenyl]isoxazole-5-
carboxylic acid 3,5-dichloro-2,6-difluoropyridin-4-
ylamide (9b, C16H8Cl2F5N3O2)
Method B, yield 25%; glass; 1H NMR (200 MHz, CDCl3):
d = 8.65 (s, 1H, NH), 7.83 (d, J = 8.3 Hz, 2H, H-50, H-30),
7.72 (d, J = 8.3 Hz, 2H, H-60, H-20), 5.43 (t, J = 8.4 Hz,
1H, H-5), 3.83 (d, J = 8.4 Hz, 2H, H-4) ppm; 13C NMR
(50.3 MHz, CDCl3): d = 168.2, 156.8, 145.4, 131.1, 127.5
(2C), 126.1 (q, J = 3.6 Hz, 2C), 79.3, 39.5 ppm; 19F NMR
(471 MHz, CDCl3): d = -63.8 (s, 3F), -88.8 (s, 2F) ppm;
IR (KBr): m = 3,220, 2,920, 2,850, 1,705, 1,602, 1,490,
1,405, 1,327, 1,175, 1,125, 1,070, 1,040, 919, 878, 840,
840, 760 cm-1
.
3-[3-(Trifluoromethyl)phenyl]isoxazole-5-carboxylic acid
2,3,5,6-tetrafluoropyridin-4-ylamide (9f, C16H6F7N3O2)
Method C, yield 69%; glass; 1H NMR (200 MHz, CDCl3):
d = 8.51 (s, 1H, NH), 8.12 (s, 1H, H-20), 8.04 (d,
J = 7.8 Hz, 1H, H-40), 7.80 (d, J = 7.8 Hz, 1H, H-60),
7.66 (t, J = 7.8 Hz, 1H, H-50), 7.52 (s, 1H, H-4) ppm; 13C
NMR (50.3 MHz, CDCl3): d = 163.1, 162.2, 152.4, 132.2
(q, J = 32.9 Hz), 130.4, 130.1, 128.5, 127.9 (q,
J = 3.6 Hz), 124.1 (q, J = 4.0 Hz), 107.8 ppm; 19F
NMR (471 MHz, CDCl3): d = -63.4 (s, 3F), -88.8 (m,
1F), -144.6 (m, 1F) ppm; IR (KBr): m = 3,410, 3,245,
2,920, 2,850, 1,699, 1,644, 1,618, 1,523, 1,464, 1,420,
1,327, 1,282, 1,240, 1,170, 1,150, 1,118, 1,076, 1,050,
788 cm-1
.
3-[4-(Trifluoromethyl)phenyl]isoxazole-5-carboxylic acid
5-chloro-2,3,6-trifluoropyridin-4-ylamide
(9c, C16H6ClF6N3O2)
Method C, yield 65%; m.p.: 211–214 ꢁC; 1H NMR
(200 MHz, CDCl3): d = 8.32 (s, 1H, NH), 8.00 (d,
J = 8.1 Hz, 2H, H-30, H-50), 7.80 (d, J = 8.1 Hz, 2H, H-
20, H-60), 7.50 (s, 1H, H-4) ppm; 13C NMR (50.3 MHz,
CDCl3): d = 162.8, 162.0, 152.0, 128.5, 127.4 (2C), 126.3
(q, J = 3.8 Hz, 2C), 107.6 ppm; 19F NMR (471 MHz,
CDCl3): d = -63.6 (s, 3F), -72.4 (dd, J = 25.9, 13.7 Hz,
1F), -86.2 (dd, J = 20.7, 13.2 Hz, 1F), -140.9 (dd,
J = 27.3, 20.7 Hz, 1F) ppm; IR (KBr): m = 3,420, 3,252,
3,130, 2,910, 2,840, 1,697, 1,625, 1,538, 1,481, 1,430,
1,400, 1,327, 1,278, 1,250, 1,170, 1,139, 1,118, 1,074,
1,000, 966, 920, 874, 810, 760, 696 cm-1
.
3-[3-(Trifluoromethyl)phenyl]isoxazole-5-carboxylic acid
5-chloro-2,3,6-trifluoropyridin-4-ylamide
(9g, C16H6ClF6N3O2)
1,050, 950, 905, 870, 850, 838, 760, 740 cm-1
.
Method C, yield 28%; glass; 1H NMR (200 MHz, CDCl3):
d = 8.11 (s, 1H, H-20), 8.01 (dm, J = 7.6 Hz, 1H, H-40),
7.76 (dm, J = 7.6 Hz, 1H, H-60), 7.64 (m, 1H, H-50), 7.32
(s, 1H, H-4) ppm; 13C NMR (50.3 MHz, (CD3)2CO):
d = 163.4, 157.4, 154.1, 131.7, 131.4, 128.4 (q,
J = 3.6 Hz), 124.6 (q, J = 3.5 Hz), 108.1 ppm; 19F
NMR (471 MHz, (CD3)2CO): d = -63.7 (3F), -75.6
(dd, J = 25.4, 14.0 Hz, 1F), -90.9 (dd, J = 25.9,
21.7 Hz, 1F), -145.1 (dd, J = 25.9, 21.7 Hz, 1F) ppm;
IR (KBr): m = 3,408, 3,200, 2,925, 2,860, 1,715, 1,662,
1,620, 1,500, 1,475, 1,400, 1,380, 1,328, 1,270, 1,171,
4,5-Dihydro-3-(2,4,5-trifluorophenyl)isoxazole-5-carbox-
ylic acid 5-chloro-2,3,6-trifluoropyridin-4-ylamide
(9d, C15H6ClF6N3O2)
Method C, yield 85%; glass; 1H NMR (200 MHz, CDCl3):
d = 8.59 (s, 1H, NH), 7.78–7.66 (dt, J = 10.5, 6.6 Hz, 1H,
H-30), 7.12–6.98 (td, J = 10.0, 6.4 Hz, 1H, H-60), 5.18 (dd,
J = 8.9, 8.5 Hz, 1H, H-5), 3.87 (d, J = 8.5 Hz, 1H, H-4),
3.86 (d, J = 8.9 Hz, 1H, H-4) ppm; 13C NMR (50.3 MHz,
CDCl3): d = 168.5, 153.4, 116.8 (ddd, J = 21.2, 6.4,
2.0 Hz), 107.1 (dd, J = 28.2, 21.2 Hz), 79.4, 41.1 (d,
J = 8.3 Hz) ppm; 19F NMR (471 MHz, CDCl3): d =
1,130, 1,074, 905, 895, 805, 696 cm-1
.
123

Synthesis and biological activity of 3-substituted isoxazolecarboxamides
469
3-[2-(Trifluoromethyl)phenyl]isoxazole-5-carboxylic acid
2,3,5,6-tetrafluoropyridin-4-ylamide (9h, C16H6F7N3O2)
Method C, yield 53%; glass; 1H NMR (200 MHz, CDCl3):
d = 8.51 (s, 1H, NH), 7.86 (m, 1H, H-30), 7.68 (m, 3H, H-
40, H-50, H-60), 7.34 (d, J = 0.8 Hz, 1H, H-4) ppm; 13C
NMR (50.3 MHz, CDCl3): d = 163.0, 160.9, 152.2, 132.2,
131.7, 130.7, 126.8 (q, J = 5.2 Hz), 110.8 (q, J = 4.8 Hz)
ppm; IR (KBr): m = 3,420, 3,207, 3,100, 3,000, 2,900,
2,840, 1,720, 1,641, 1,604, 1,537, 1,470, 1,420, 1,400,
1,316, 1,280, 1,227, 1,192, 1,124, 1,060, 1,039, 1,005, 968,
(NH2C6H4Br, 100), 145 (C6H4CF3, 15), 69 (CF3, 12), 43
(CH[CH3]2, 10).
Biological assay
The compounds were screened for fungicidal activity in
two types of tests. The in vitro test carried out for Fusarium
culmorum Sacc., Phytophthora cactorum Schroek, Alter-
naria alternata Keissl. (Fr.), Rhizoctonia solani Kuhn, and
Botrytis cinerea Pers. Ex Fr involved determination of
mycelial growth retardation in potato-glucose agar (PGA).
Stock solutions of test chemicals in acetone were added to
agar medium to give a concentration of 200 or 20 lg cm-3
and dispersed into Petri dishes. Four discs containing test
fungus were placed at intervals on the surface of the
solidified agar, and the dishes were then inoculated for
4–8 days depending on the growth rate of the control
samples, after which fungal growth was compared with
that in untreated control samples. An in vivo test assayed
the retarding effect of the compounds on germination
of Erysiphe graminis Tritici spores. The wheat seedlings
were sprayed with a solution of the test chemical at
1,000 lg cm-3, and the plants were infected with spores of
the fungus 24 h later. The fungicidal activity was expressed
as the percentage of plant infection compared to that on the
control.
865, 775, 700 cm-1
.
4,5-Dihydro-5-methyl-3-(2,3,6-trichlorophenyl)isoxazole-
4-carboxylic acid 4-bromophenyl amide
(10, C17H12BrCl3N2O2)
Method B, yield 19%; glass; 1H NMR (200 MHz, CDCl3):
d = 7.50 (d, J = 8.7 Hz, 1H, H-40), 7.40 (d, J = 8.7 Hz,
2H, H-200, H-600), 7.34 (d, J = 8.7 Hz, 1H, H-50), 7.24 (d,
J = 8.7 Hz, 2H, H-300, H-500), 5.39 (quint, J = 6.2 Hz, 1H,
H-5), 4.17 (d, J = 6.2 Hz, 1H, H-4), 1.59 (d, J = 6.2 Hz,
3H, CH3) ppm; 13C NMR (50.3 MHz, CDCl3): d = 170.9,
155.2, 135.9, 135.7, 133.9, 133.7, 132.9 (2C), 132.7, 132.5,
132.4, 129.9, 121.7 (2C), 72.6, 68.1, 14.1 ppm; IR (KBr):
m = 3,370, 3,292, 3,080, 2,980, 1,663, 1,595, 1,515, 1,489,
1,441, 1,396, 1,305, 1,287, 1,240, 1,179, 1,072, 1,009, 920,
819, 780, 725 cm-1; EIMS: m/z (%) = 461 (M?, 40).
4,5-Dihydro-3-(4-isopropylphenyl)-5-[4-(trifluoro-
methyl)phenyl]isoxazole-4-carboxylic
Acknowledgments This work was supported in part by the Polish
Ministry of Science and Higher Education Research (Grant 429E-142/
S/2008), which is gratefully acknowledged.
acid 4-bromophenylamide (11, C26H22BrF3N2O2)
Method A, yield 48%; m.p.: 247–250 ꢁC; 1H NMR
(200 MHz, CDCl3): d = 7.70 (d, J = 8.6 Hz, 2H, H-500,
H-300), 7.65 (d, J = 8.4 Hz, 2H, H-20, H-60), 7.54 (d,
J = 8.6 Hz, 2H, H-200, H-600), 7.43 (d, J = 9.0 Hz, 2H, H-
3¢¢¢, H-5¢¢¢), 7.34 (d, J = 9 Hz, 2H, H-2¢¢¢, H-6¢¢¢), 7.33 (d,
J = 8.4 Hz, 2H, H-50, H-30), 6.08 (d, J = 3.8 Hz, 1H, H-
5), 4.37 (d, J = 3.8 Hz, 1H, H-4), 2.93 (sept, J = 6.9 Hz,
1H, CHCH[CH3]2), 1.24 (d, J = 6.9 Hz, 6H, CH[CH3]2)
ppm; 13C NMR (50.3 MHz, CDCl3): d = 167.2, 154.6,
151.5, 145.1, 138.2, 132.0 (2C), 128.2, 127.1 (2C),
127.1 (2C), 127.0 (2C), 125.9 (2C, q, J = 3.6 Hz), 121.7
(2C), 87.0, 64.2, 34.0, 23.3 ppm; 19F NMR (471 MHz,
CDCl3): d = -63.1 (3F) ppm; IR (KBr): m = 3,443,
2,965, 1,658, 1,539, 1,489, 1,398, 1,327, 1,167, 1,125,
1,068, 1,010, 900, 830 cm-1; EIMS: m/z (%) = 532, 530
(M?, 2), 215 (M?–NHC6H4BrC6H4CF3, 20), 188 (M?–
NHC6H4BrC6H4CF3CO, 24), 172 (NHC6H4Br, 82), 173
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