Studies with enamines: Synthesis and reactivity of 4-nitrophenyl-1- piperidinostyrene. Synthesis of pyridazine, oxadiazole, 1,2,3-triazole and 4-aminopyrazole derivatives

Article abstract of DOI:10.1515/znb-2007-0218

4-Nitrophenyl-1-piperidinostyrene (4) reacts with an aromatic diazonium salt to afford the arylhydrazonal 6. The latter condenses with active methylene compounds to yield pyridazine derivatives, and with hydroxylamine hydrochloride to produce oxadiazole a

Full text of DOI:10.1515/znb-2007-0218

Studies With Enamines: Synthesis and Reactivity of
4-Nitrophenyl-1-piperidinostyrene. Synthesis of Pyridazine,
Oxadiazole, 1,2,3-Triazole and 4-Aminopyrazole Derivatives
Tayseer A. Abdallah, Abdellatif M. Salaheldin, and Naglaa F. Radwan
Department of Chemistry, Faculty of Science, Cairo University, Giza, A. R. Egypt
Reprint requests to Dr. A. M. Salaheldin. E-mail: amsalaheldin@yahoo.com
Z. Naturforsch. 2007, 62b, 261 – 266; received October 19, 2006
4-Nitrophenyl-1-piperidinostyrene (4) reacts with an aromatic diazonium salt to afford the aryl-
hydrazonal 6. The latter condenses with active methylene compounds to yield pyridazine derivatives,
and with hydroxylamine hydrochloride to produce oxadiazole and 1,2,3-triazole derivatives. Com-
pound 12 was reacted with chloroacetonitrile to afford 4-aminopyrazoles 15.
Key words: 2-Arylhydrazononitriles, Pyridazinimine, Oxadiazole, 1,2,3-Triazole,
4-Aminopyrazoles
Introduction
afforded the enamine 4 in good yield. Utilization of tri-
ethyl orthoformateand piperidine in DMF solution was
found more economic and safer than using DMFDMA.
It is believed that piperidine reacts with acetal 1 which
then condenses with 2 to yield 3, which is readily de-
carboxylated into the final isolated product 4 as de-
picted in Scheme 1.
Enamines are versatile reagents that are currently
utilized extensively as synthetic equivalents of aldehy-
des [1 – 5]. In earlier work we have shown that func-
tionally substituted enamines are versatile precursors
to otherwise not readily obtainable active methylene
aldehydes [6 – 8]. In conjunction with this work, we
report here a synthesis of the title compound 4 and its
use as a 4-nitrophenylacetaldehyde equivalent for the
synthesis of different heteroaromatic compounds such
as pyridazines, 4-aminopyrazoles and 1,2,3-triazoles
(Scheme 1). The strategy adopted herein for the syn-
thesis of the target compound 4 is based on the use
of 4-nitrophenylacetic acid (2).
The possibility that decarboxylation preceded con-
densation was ruled out based on the failure of attempts
to condense 4-nitrotoluene with orthoformate under
the same reaction conditions. Although it was earlier
reported that nitrotoluenes condense with DMFDMA
to yield enamines [9], we failed to repeat this work.
1
The H NMR spectrum of compound 4 showed two
singlet signals for the piperidinyl protons at δ = 1.64
(3 CH2) and 3.20 (2 CH2) ppm and two doublets at δ =
5.30 and 6.96 ppm for the two olefinic protons. The
Result and Discussion
The reaction of 4-nitrophenylacetic acid (2) with olefinic coupling constant (3J = 14 Hz) indicated that
triethyl orthoformate and piperidine in DMF solution the reaction product exists solely in the E-form 4. The
Scheme 1.
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262
T. A. Abdallah et al. · Synthesis and Reactivity of 4-Nitrophenyl-1-piperidinostyrene
Scheme 2.
Z-isomer 5 was not detected by NMR. 13C NMR and with malononitrile in ethanol in the presence of a cat-
mass spectra of compound 4 are in accordance with the alytic amount of triethylamine to yield compound 9
proposed structure.
which was coupled with an aromatic diazonium salt to
afford compound 7a. Compound 7a was cyclized into
the pyridazinimine 8a by heating in ethanolic triethy-
lamine solution (m. p., mixed m. p. and TLC control).
Compound 8a could be converted into 8b by refluxing
compound 8a in ethanolic hydrochloric acid as indi-
cated in Scheme 2 [14, 15].
The considerable biological activities of pyridazine
derivatives have incited considerable interest in de-
veloping efficient synthetic approaches for differently
substituted pyridazine derivatives [10 – 13]. Com-
pound 4 proved to be a perfect synthetic equivalent
for 4-nitrophenylacetaldehyde to produce pyridazine
derivatives. Thus, it coupled readily with aromatic di-
The utility of 2-arylhydrazonoaldehydes in hetero-
azonium salts to yield the arylhydrazonals 6. It re- cyclic synthesis has received a considerable interest in
acted with malononitrile and ethyl cyanoacetate to af- the past decade [7, 8]. Compound 6 reacted with hy-
ford compounds 8a, b. Establishing of their structures droxylamine hydrochloride in ethanol in the presence
was based on the elemental analyses and spectral data. of triethylamine to afford the oxime 10, similar to an
Compound 8a was converted quantitively into pyri- earlier report on arylhydrazonals[7]. In refluxing aque-
dazinone 8b by treatment with ethanolic hydrochloric ous acetic acid and in the presence of sodium acetate,
acid solution as shown in Scheme 2 [14, 15].
compound 6 reacted with hydroxylamine hydrochlo-
ride to yield 2-arylhydrazononitrile 12, formed via in-
termediacy of the oxime acetate 11.
Establishing of structure 8 was based on the spectral
analysis. For example, the IR spectra of compound 8a
showed an NH stretching band at 3363 cm−1 and a
Compound 12 has also been obtained from treat-
strong band at 2196 cm−1 for the CN group. In case ment of oxime 11 with acetic acid/ammonium ac-
of 8b, a C=O absorption band at 1681 cm−1 in ad- etate solution. It is believed that 11 was acylated in
dition to a CN band at 2235 cm−1 was found. The acetic acid solution and that the acylated compound 11
1H NMR spectra of compound 8a revealed, in addition derivative underwent thermal elimination of acetic acid
to the aromatic protons, the presence of a singlet at δ = to yield 12 (Scheme 3).
7.63 ppm corresponding to pyridazinimine 4-H and a
singlet at δ = 8.58 ppm correspondingto NH. The mass
spectra of the products are in accordance with the pro-
posed structure (cf. Experimental Section).
Treatment of compound 6 with acetic anhydride at
reflux afforded the oxadiazole derivative 13, whereas
refluxing of 10 in acetic anhydride yielded the 1,2,3-
triazole derivative 14. The structures of 13 and 14 were
The structures of compounds 8a, b were confirmed established based on their elemental analysis and spec-
by their alternative synthesis via refluxing compound 4 tral data. For example, the 1H NMR spectrum of com-
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T. A. Abdallah et al. · Synthesis and Reactivity of 4-Nitrophenyl-1-piperidinostyrene
263
Scheme 3.
pound 13 revealed the presence of a singlet at δ = 4-Nitrophenyl-1-piperidinostyrene (4)
2.66 ppm corresponding to a CH3 group, a multiplet
A mixture of 4-nitrophenyl acetic acid (0.5 mol), triethyl
orthoformate (0.5 mol) and piperidine (0.5 mol) was treated
with 50 mL of DMF and refluxed for 72 h. The reaction mix-
ture was then cooled to r. t. and poured onto water. The solid
product, so formed, was collected by filtration and crystal-
lized from ethanol. M. p. 98 – 99 ◦C. Yield: 75 %. – IR (KBr):
ν = 2853 (CH aliphati◦c), 1629 (C=C) cm−1. – 1H NMR
(300 MHz, CDCl3, 25 C, TMS): δ = 1.64 (s, 6H, 3CH2),
3.20 (s, 4H, 2CH2), 5.30 (d, J = 14 Hz, 1H, CH), 6.94 (d,
J = 14 Hz, 1H, CH), 7.16 (d, J = 9 Hz, 2H, Ar-H), 8.04 (d,
J = 9 Hz, 2H, Ar-H). – 13C NMR (75 MHz, [D6]DMSO):
δ = 23.8, 25.2, 48.9, 94.7 (HC=CH), 122.2, 124.2, 141.1
(HC=CH), 144.7, 149.0. – MS (EI, 70 eV): m/z (%) = 232
(36) [M+]. – C13H16N2O2 (232.27): calcd. C 67.22, H 6.94,
N 12.06; found C 66.95, H 6.80, N 12.22.
at δ = 7.30– 8.35 ppm corresponding to aromatic pro-
tons and a singlet at δ = 9.86 ppm corresponding
to NH. The mass spectrum of the product was consis-
tent with these results. Again compound 13 could also
be obtained by refluxing the 2-aryl-hydrazononitrile12
with hydroxylamine hydrochloride in acetic anhydride
for 4 h (m. p., mixed m. p. and TLC control). The
1H NMR spectrum of compound 14 revealed in addi-
tion to the aromatic protons a singlet at δ = 8.15 ppm
corresponding to the triazole proton 5-H.
Compound 12, so formed, proved to be a valuable
precursor to arylazoles. For example, reacting 12 with
chloroacetonitrile afforded 4-aminopyrazole 15, rela-
tives of which have been described recently [16].
2-[2-(4-Chlorophenyl)hydrazono]-2-(4-nitrophenyl)-
acetaldehyde (6)
Experimental Section
All melting points were measured with a Gallenkamp
A cold solution of arenediazonium chloride (10 mmol)
electrothermal melting point apparatus and are uncorrected. was prepared by adding a solution of sodium nitrite (10 mmol
IR spectra were recorded as KBr pellets with a Pye Uni- in 2 mL of H2O) to a cold solution of the aromatic amine
cam SP 3-300 Spectrophotometer. 1H and 13C NMR spectra hydrochloride with stirring. The resulting solution of the
were recorded in deuterated dimethylsulfoxide [D6]DMSO arenediazonium chloride was added to a cold solution of 1-
or deuterated chloroform (CDCl3) at 300 MHz with a Varian (4-nitrostyryl)piperidine (4) in ethanol (50 mL) containing
Gemini NMR spectrometer using tetramethylsilane (TMS) sodium acetate (5 g). The reaction mixture was stirred at r. t.
as an internal reference, and results are expressed as δ val- for 30 min. The solid product, so formed, was collected by
ues. Mass spectra were performed on a Shimadzu GCMS-QP filtration, washed with water and crystallized from ethanol.
1000 Ex mass spectrometer at 70 eV. Elemental analyses M. p. 210 – 212 ◦C. Yield: 70 %. – IR (KBr): ν = 3423 (NH),
were carried out at the Microanalytical Center of Cairo Uni- 170◦0 (C=O) cm−1. – 1H NMR (300 MHz, [D6]DMSO,
versity.
25 C, TMS): δ = 7.16 (d, J = 9 Hz, 2H, Ar-H), 7.41 (d,
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T. A. Abdallah et al. · Synthesis and Reactivity of 4-Nitrophenyl-1-piperidinostyrene
J = 9 Hz, 2H, Ar-H), 7.66 (d, J = 9 Hz, 2H, Ar-H), 8.32 (d, 5-H), 7.85 – 8.27 (m, 4H, Ar-H), 8.58 (s, 1H, NH). – MS
J = 9 Hz, 2H, Ar-H), 9.56 (s, 1H, CHO), 11.0 (s, 1H, NH). – (EI, 70 eV): m/z (%) = 351 (100) [M+], 353 (33) [M++2].
MS (EI, 70 eV): m/z (%) = 303 (72) [M+], 305 (23) [M++2]. – C17H10ClN5O2 (351.7): calcd. C 58.05, H 2.87, N 19.91,
– C14H10ClN3O3 (303.7): calcd. C 55.37, H 3.32, N 13.84, Cl 10.08; found C 57.80, H 2.80, N 20.17, Cl 10.30.
Cl 11.67; found C 55.26, H 3.10, N 13.75, Cl 11.60.
2-(4-Chlorophenyl)-2,3-dihydro-6-(4-nitrophenyl)-3-oxo-
pyridazine-4-carbonitrile (8b)
2-[2-[(4-Chlorophenyl)hydrazono]-2-(4-nitrophenyl)
ethylidene]malononitrile (7a)
M. p. 270 – 272 ◦C (EtOH/DMF, 3 : 1). Yield: 74 %. –
.
A cold solution of arenediazonium chloride (10 mmol)
was prepared by adding a solution of sodium nitrite (10 mmol
in 2 mL of H2O) to a cold solution of the aromatic amine
hydrochloride with stirring. The resulting solution of the
arenediazonium chloride was added to a cold solution of 9
in ethanol (50 mL) containing sodium acetate (5 g). The
reaction mixture was stirred at r. t. for 30 min. The solid
product, so formed, was collected by filtration, washed with
water and crystallized from ethanol. M. p. 130 – 132 ◦C.
Yield: 72 %. – IR (KBr): ν = 3340 (NH), 2220, 2208 (CN),
1610 (C=C) cm−1. – MS (EI, 70 eV): m/z (%) = 351 (36)
[M+], 353 (11) [M++2]. – C17H10ClN5O2 (351.74): calcd.
C 58.05, H 2.87, N 19.91, Cl 10.08; found C 57.95, H 3.05,
N 19.77, Cl 10.18.
IR (KBr): ν = 2235 (CN), 1681 (C=O) cm−1. – 1H NMR
(300 MHz, [D6]DMSO, 25 ◦C, TMS): δ = 7.56 (d, J = 9 Hz,
2H, Ar-H), 7.92 (d, J = 9 Hz, 2H, Ar-H), 8.19 (d, J = 9 Hz,
2H, Ar-H), 8.35 (d, J = 9 Hz, 2H, Ar-H), 9.08 (s, 1H, 5-H). –
MS (EI, 70 eV): m/z (%) = 352 (75) [M+], 354 (23) [M++2].
– C14H10ClN3O3 (352.73): calcd. C 57.89, H 2.57, N 15.88,
Cl 10.05; found C 57.66, H 2.70, N 15.75, Cl 10.30.
2-[2-(4-Nitrophenyl)vinyl]malononitrile (9)
A mixture of 4 (2.32 g, 10 mmol), malononitrile (0.66 g,
10 mmol) and triethylamine (1.01 g, 10 mmol) in ethanol
(25 mL) was refluxed for 3 h. The solvent was evaporated un-
der vacuum, and the crude product was collected and crystal-
lized from ethanol. M. p. 80 – 81 ◦C. Yield: 80 %. – IR (KBr):
General procedure for the preparation of pyridazine deriva-
tives 8a, b
1
ν = 2201 (CN), ◦1601 (C=C) cm−1. – H NMR (300 MHz,
[D6]DMSO, 25 C, TMS): δ = 4.44 (s, 1H, CH), 7.25 (d,
J = 9 Hz, 1H, CH), 7.80 (d, J = 9 Hz, 1H, CH), 7.90 – 8.35
(m, 4H, Ar-H). – MS (EI, 70 eV): m/z (%) = 213 (31) [M+].
– C11H7N3O2 (213.19): calcd. C 61.97, H 3.31, N 19.71;
found C 61.65, H 3.35, N 19.75.
Method A: a mixture of 2-arylhydrazonal 6 (10 mmol)
and malononitrile or ethyl cyanoacetate (10 mmol of each)
was refluxed in ethanol (50 mL) for 3 h in the presence of
triethylamine. The solvent was evaporated in vacuo and the
solid residue was collected by filtration and crystallized from
ethanol.
2-(4-Chlorophenylhydrazono)-2-(4-nitrophenyl)ethanal-1-
Method B: To a solution of 7a (10 mmol) in 30 mL of
ethanol was added 1 mL of triethylamine, and the solution
was refluxed for 1 h. After cooling to r. t. the reaction mixture
was diluted with cold water and neutralized with hydrochlo-
ric acid. The precipitate was collected by filtration and crys-
tallized to afford a product, which was identical to 8a in all
respects.
oxime (10)
A warm solution of hydroxylamine hydrochloride (0.69 g,
10 mmol) and sodium carbonate (1.26 g, 12 mmol) in wa-
ter (10 mL) was added to a stirred solution of the arylhy-
drazonoethanal (6) (10 mmol) in ethanol (4 mL). The re-
action mixture was stirred at r. t. for 4 h. The oximes soon
separated as semisolid crystals that were solidified by cool-
ing in crushed ice. The solid product, so formed, was col-
lected by filtration and crystallized from ethanol/DMF (3 : 1).
M. p. 270 – 272 ◦C. Yield: 77 %. – IR (KBr): ν = 3365 (OH),
3206 (NH) cm−1. – 1H NMR (300 MHz, [D6]DMSO, 25 ◦C,
TMS): δ = 7.05 (d, J = 9 Hz, 2H, Ar-H), 7.20 (s, 1H, CH),
7.44 (d, J = 9 Hz, 2H, Ar-H), 7.60 (d, J = 10 Hz, 2H, Ar-H),
8.16 (d, J = 10 Hz, 2H, Ar-H), 8.24 (s, 1H, NH), 8.88 (s, 1H,
OH). – MS (EI, 70 eV): m/z (%) = 318 (80) [M+], 320 (26)
[M++2]. – C14H11ClN4O3 (318.75): calcd. C 52.76, H 3.48,
N 17.58, Cl 11.12; found C 52.89, H 3.35, N 17.75, Cl 11.22.
Transformation of 8a to 8b
To a solution of 3.03 g (10 mmol) of 8a in 30 mL of
ethanol was added conc. HCl (5 mL) and the solution was
refluxed for 1 h. After cooling to r. t. the reaction mixture
was diluted with cold water and neutralized with ammonia.
The precipitate was collected by filtration and crystallized to
afford a product, which was identical to 8b in all respects.
2-(4-Chlorophenyl)-2,3-dihydro-3-imino-6-(4-nitro-
phenyl)pyridazine-4-carbonitrile (8a)
(4-Chlorophenyl)hydrazono-(4-nitrophenyl)acetonitrile (12)
Method A: A mixture of hydroxylamine hydrochloride
25 C, TMS): δ = 7.20 – 7.53 (m, 4H, Ar-H), 7.63 (s, 1H, (0.69 g, 10 mmol), sodium acetate (3 g) and arylhydrazo-
.
◦
M. p. 175 – 177 C. Yield: 70 %. – IR (KBr): ν = 3363
(NH), 2196 (CN) cm−1. – 1H NMR (300 MHz, [D6]DMSO,
◦
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T. A. Abdallah et al. · Synthesis and Reactivity of 4-Nitrophenyl-1-piperidinostyrene
265
noethanal (6) (10 mmol) was refluxed in acetic acid (20 mL) (m, 4H, Ar-H), 9.86 (s, 1H, NH). – MS (EI, 70 eV): m/z (%) =
for 4 h. The solvent was removed under vacuum and the 357 (13) [M+]. – C16H12ClN5O3 (357.75): calcd. C 53.72,
residue was poured onto water. The solid product was col- H 3.38, N 19.58, Cl 9.91; found C 53.60, H 3.40, N 19.38,
lected by filtration and crystallized from ethanol.
Cl 9.60.
Method B: The oxime 10 (10 mmol) was refluxed in acetic
acid (10 mL) and ammonium acetate (3 g) for 4 h, and
then left to cool at r. t. The solvent was reduced under vac-
uum and the residue was poured onto water. The solid prod-
uct was collected by filtration and crystallized from ethanol.
M. p. 200 – 201 ◦C. Yield: 80 %. – IR (KBr): ν = 3380 (NH),
2208 (CN) cm−1. – 1H NMR (300 MHz, [D6]DMSO, 25 ◦C,
TMS): δ = 6.99 – 7.25 (m, 4H, Ar-H), 7.30 (s, 1H, NH), 7.75
(d, J = 10 Hz, 2H, Ar-H), 8.22 (d, J = 10 Hz, 2H, Ar-H). –
13C NMR (75 MHz, [D6]DMSO): δ = 157.2 (C=N), 155.2,
144.1, 137.4, 130.2, 129.1, 124.5, 123.4, 120.2, 117.2 (CN).
– MS (EI, 70 eV): m/z (%) = 300 (25) [M+], 302 (8) [M++2].
– C14H9ClN4O2 (300.70): calcd. C 55.92, H 3.02, N 18.63,
Cl 11.79; found C 55.75, H 2.90, N 18.90, Cl 11.94.
2-(4-Chlorophenyl)-4-(4-nitrophenyl)-2H-[1,2,3]triazole
(14)
The oxime 11 (10 mmol) was refluxed in acetic anhydride
(10 mL) for 4 h, and then left to cool at r. t. The solid prod-
uct separated was collecte◦d by filtration and crystallized from
ethanol. M. p. 150 – 152 C. Yield: 55 %. – IR (KBr): ν =
2925 (CH-Ar), 1601 (C=N) cm−1. – 1H NMR (300 MHz,
CDCl3, 25 ◦C, TMS): δ = 7.48 (d, J = 9 Hz, 2H, Ar-H), 7.61
(d, J = 9 Hz, 2H, Ar-H), 8.04 (d, J = 9 Hz, 2H, Ar-H), 8.32
(d, J = 9 Hz, 2H, Ar-H), 8.15 (s, 1H, triazole 5-H). – MS
(EI, 70 eV): m/z (%) = 300 (69) [M+], 302 (24) [M++2].
– C14H9ClN4O2 (300.75): calcd. C 55.92, H 3.02, N 18.63,
Cl 11.79; found C 55.70, H 3.17, N 18.51, Cl 11.95.
2-(4-Chlorophenyl)-1-(5-methyl-1,2,4-oxadiazol-3-yl)-
(4-nitrophenyl)methylene hydrazine (13)
4-Amino-2-(4-chlorophenyl)-5-(4-nitrophenyl)-2H-
pyrazole-3-carbonitrile (15)
Method A: A mixture of hydroxylamine hydrochloride
(0.69 g, 10 mmol), and arylhydrazonoethanal (6) (10 mmol)
was refluxed in acetic anhydride (20 mL) for 6 h. The sol-
vent was removed under vacuum and the residue was poured
onto water. The solid product was collected by filtration and
crystallized from ethanol.
Method B: A mixture of hydroxylamine hydrochloride
(0.69 g, 10 mmol) and arylhydrazononitrile 12 (10 mmol)
was refluxed in acetic anhydride (10 mL) for 4 h, and then
left to cool at r. t. The solvent was removed under vacuum
and the residue was poured onto water. The solid product
To a solution of 12 (3.0 g, 10 mmol) in dioxane (25 mL)
and triethylamine (1.01 g, 10 mmol), chloroacetonitrile
(1 mL, 0.016 mol) was added. The reaction mixture was re-
fluxed for 3 h and then the solvent evaporated in vacuo; the
solid product was filtered off and crystallized from ethanol.
M.p. 187 – 188 ◦C. Yield: 85 %. – IR (KBr): ν = 3451, 3348
(NH2), 2217 (CN) cm−1. – 1H NMR (300 MHz, [D6]DMSO,
◦
25 C, TMS): δ = 6.49 (s, 2H, NH2), 7.25 – 7.48 (m, 4H,
Ar-H), 7.55 (d, J = 10 Hz, 2H, Ar-H), 8.20 (d, J = 10 Hz,
2H, Ar-H). – 13C NMR (75 MHz, [D6]DMSO): δ = 145.2,
143.0 (C-3), 141.6, 139.3, 137.6, 135.9 (C-4), 134.6, 128.8,
124.5, 122.2, 119.7 (C-5), 117.9 (CN). – MS (EI, 70 eV): m/z
was collected by filtration and crystallized from ethanol.
M. p. 120 – 122 C. Yield: 55 %. – IR (KBr):◦ν = 3396 (%) = 339 (37) [M+], 341 (11) [M++2]. – C16H10ClN5O2
◦
(NH) cm−1. – 1H NMR (300 MHz, CDCl3, 25 C, TMS):
(339.74): calcd. C 56.56, H 2.97, N 20.61, Cl 10.44; found
δ = 2.66 (s, 3H, CH3), 7.30 – 7.60 (m, 4H, Ar-H), 7.69 – 8.35 C 56.42, H 3.10, N 20.30, Cl 10.50.
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