CINNAMOYLACETONITRILE ARYLHYDRAZONES IN HETEROCYCLIC SYNTHESIS: SIMPLE SYNTHESIS OF PYRIDAZINES AND THEIR CONDENSED DERIVATIVES

Article abstract of DOI:10.1135/cccc19940186

A new route for the synthesis of the title ring systems starting with the cinnamoylacetonitrile arylhydrazones (Ia, Ib) is described.It involves the self-cyclization of I which was found to be pH dependent.

Full text of DOI:10.1135/cccc19940186

186
Nawwar, Swellem, Chabaka:
CINNAMOYLACETONITRILE ARYLHYDRAZONES IN HETEROCYCLIC
SYNTHESIS: SIMPLE SYNTHESIS OF PYRIDAZINES AND THEIR
CONDENSED DERIVATIVES
Galal A. M. NAWWAR, Randa H. SWELLEM and Laila M. CHABAKA
National Research Centre, Dokki, Cairo, Egypt
Received June 30, 1992
Accepted December 4, 1992
A new route for the synthesis of the title ring systems starting with the cinnamoylacetonitrile arylhy-
drazones (Ia, Ib) is described. It involves the self-cyclization of I which was found to be pH depend-
ent.
3-Oxoalkanonitriles are versatile reagents and their chemistry has received considerable
attention1. Several heterocyclic compounds could be prepared on utilizing benzoyl-
acetonitrile2,3. When cinnamoylacetonitrile was used instead of the benzoyl derivative,
a broader variety of heterocycles were synthesized also through simple methods4,5. Re-
cently, we have reported a novel approach to the synthesis of pyrano[2,3-d]pyridazines
starting with the hydrazones Ia and Ib. We became interested in proving that these
available hydrazones can be utilized as convenient precursors for the synthesis of pyri-
dazines annulated with various five and six membered heterocycles.
Thus, we were able to synthesize our previously reported pyridazine derivatives IIa
and IIb in a better yield and simpler procedure by keeping solutions of the hydrazones
Ia and Ib in tetrahydrofuran at 25 °C for 48 h in presence of catalytic amounts of
concentrated sulfuric acid: an acid induced self-cyclization occurred affording com-
pounds IIa and IIb. On reacting of compound Ia with hydrazine hydrate in boiling
ethanol, only a complicated mixture was formed. On the other hand, when the reaction
was conducted at room temperature (25 °C) a product of a molecular formula C17H15N5
(m/z 289) was obtained. Two structures seemed possible for this product (cf. structures
IIIa and IVa in Scheme 1). Structure IIIa was confirmed by the spectral data and chemi-
1
cal behaviour. The H NMR spectrum revealed a pyrazoline ring (H-5) signal at δ 4.9
ppm. If the product was the pyridazine derivative IVa one would expect the same
proton signal (H-6) at downfield shift6. In accordance with this view, the same py-
razoline product IIIa was obtained when the pyridazine derivative IIa was allowed to
react with hydrazine hydrate at 25 °C.
Similarly, the pyrazoline IIIb was obtained in satisfactory yield from the reaction of
hydrazine hydrate with either Ib or IIb on applying the above mentioned experimental
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SCHEME 1
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Nawwar, Swellem, Chabaka:
TABLE I
Yields, melting points and analytical data of compounds III – X, XIII, and XVI
Calculated/Found
M. p., °C
solvent
Formula
(M. w.)
Compound Yield, %
% C
% H
% Cl
% N
IIIa
IIIb
IVa
IVb
Va
75
70
60
63
45
45
70
65
60
55
70
63
40
35
50
53
90
ether
C17H15N5
70.57
70.39
5.23
5.02
–
–
24.20
23.95
(289.3)
99
ether
C17H14ClN5
(323.8)
63.06
62.87
4.36
4.20
10.95
10.52
21.63
21.37
218 – 220
dioxane
C17H15N5
(289.3)
70.56
70.41
5.22
4.97
–
–
24.21
24.00
224
dioxane
C17H14ClN5
(323.8)
63.06
62.79
4.36
4.13
10.95
10.63
21.63
21.40
250 – 252
dioxane
C17H15N5
(289.3)
70.56
70.36
5.22
5.00
–
–
24.21
23.86
Vb
263
dioxane
C17H14ClN5
(323.8)
63.06
62.74
4.36
4.07
10.95
10.59
21.63
21.40
VI
128
dioxane
C23H17N7O4
(455.4)
60.66
60.43
3.76
3.51
–
–
21.53
21.24
VII
215
ethanol
C19H17N5O
(331.4)
68.87
68.77
5.17
5.00
–
–
21.13
20.87
VIII
IX
183
ethanol
C21H18ClN5O2
(407.9)
61.84
61.61
4.45
4.35
8.69
8.40
17.17
16.85
194
dioxane
C21H18ClN5O2
(407.9)
61.84
61.74
4.45
4.12
8.69
8.48
17.17
17.00
Xa
220
methanol
C17H16N4O2
(308.3)
66.22
66.19
5.23
5.01
–
–
18.17
17.95
Xb
228
methanol
C17H15ClN4O2
(342.8)
59.57
59.28
4.41
4.30
10.34
9.98
16.34
16.00
XIIIa
XIIIb
XVIa
XVIb
255
dioxane
C17H13N4O
(289.3)
70.58
70.36
4.53
4.37
–
–
19.37
19.03
267
dioxane
C17H12ClN4O
(323.8)
63.07
62.79
3.74
3.56
10.95
10.61
17.30
17.17
>300
ethanol
C23H17N7O
(407.4)
67.80
67.63
4.21
4.00
–
–
24.06
23.65
>300
ethanol
C23H16ClN7O
(441.9)
62.52
62.40
3.65
3.37
8.02
7.71
22.19
21.78
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Pyridazines and their Condensed Derivatives
189
conditions. Based on these data, it could be deduced that the self-cyclization of the
hydrazones I to form pyridazines II is a pH dependent reaction and the N(1)−C(6) bond
in these pyridazines splits with remarkable ease at alkaline pH as we have previously
reported6. To make use of this behaviour, we have carried out the reaction of the pyri-
dazines IIa and IIb with hydrazine hydrate in presence of sulfuric acid as a catalyst.
The hydrazonopyridazines IVa and IVb were obtained in this case instead of the py-
razoles IIIa and IIIb. Structure IV was established through elemental analyses and spec-
tral data (cf. Table I).
Cyclization of compounds IVa and IVb could be achieved by heating at 220 °C to
afford the aimed pyrazolo[4,3-c]pyridazines Va and Vb, respectively. Their structures
were established based on elemental analyses and spectral data; the IR spectra showed
the absence of the C≡N group.
In accordance with these results, the hydrazone Ia condensed readily with 2,4-dini-
trophenylhydrazine in presence of sulfuric acid to give a deep red product of molecular
formula C23H17N7O4 (m/z 455) which could be formulated as the hydrazono- pyridazine
derivative VI according to elemental analysis and spectral data (cf. Table I). Several
attempts for the cyclization of VI in order to prepare the corresponding pyrazolo[4,3-
c]pyridazine derivative were carried out but none of them was successful.
Continuing our interest in the synthesis of pyridazines, compound IIIa was acetylated
with acetic anhydride affording the N-acetylpyrazole VII which could be further acy-
lated with chloroacetyl chloride in presence of one equivalent of sodium hydride to
give the N,N′-diacylpyrazole derivative VIII. Structures of compounds VII and VIII
were established based on their elemental analyses and spectral data (cf. Table I). The
chemical behaviour of compound VIII was also in full accordance with the N,N′-diacyl
structure. Thus, when it was boiled under reflux in xylene in the presence of one equi-
valent of sodium hydride, a product with a molecular formula C21H17ClN5O2 (m/z 406)
was obtained. The 3-(3-pyrazolyl)pyridazine structure IX was suggested for this prod-
1
uct on the basis of elemental analysis and spectral data. Its H NMR spectrum showed
a pyrazoline protons pattern similar to that present in the parent compound in addition
to a (D2O) exchangeable signal at δ 4.8 ppm attributable to the amino group protons.
While the IR spectrum revealed the absence of the cyano group absorption and showed
a broad absorption at 3 300 – 3 200 cm−1 assigned to the amino group absorption plus
two carbonyl group absorptions at 1 650 and 1 680 cm−1 attributable to the acetyl and
pyridazine carbonyl groups absorptions, respectively.
The behaviour of the arylhydrazones Ia and Ib towards hydroxylamine hydrochloride
was also investigated under different experimental conditions. Thus, it has been found
that Ia could react with hydroxylamine hydrochloride in presence of pyridine to yield a
product of a molecular formula C17H16N4O2 (m/z 308). Its IR spectrum showed the
absence of the cyano group and the presence of a carbonyl absorption at 1 650 cm−1
beside a broad absorption band at 3 150 – 3 250 cm−1 assignable to an amino group.
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Nawwar, Swellem, Chabaka:
1
Moreover, the H NMR spectrum showed ABX system, attributable to the CH2−CH
moiety; this characteristic protons pattern was previously observed in our report on
tetrahydro-4-oxopyridazine derivatives6 and accordingly structure Xa was given for the
product. An analogous result was obtained from the reaction of Ib with hydroxylamine
hydrochloride affording Xb under the same experimental conditions (see Scheme 2). It
is assumed that the formation of X occurred via the intermediacy of the pyridazine II
which subsequently reacted with hydroxylamine to afford the final product. In accord-
ance with this view, compound Xa was obtained when the pyridazine IIa was allowed
to react with hydroxylamine hydrochloride under similar reaction conditions.
If the hydrazones I reacted with hydroxylamine prior to its cyclization, other types of
cyclizations would be expected to compete with the proposed structure as observed
when the reaction was carried out in presence of aqueous potassium hydroxide. Instead
of the pyridazines isoxazolopyridazines XIIIa and XIIIb were obtained. The IR spec-
trum of XIIIa showed absence of the cyano group absorption which ruled out the
possible formation of the isoxazole derivative corresponding to the pyrazole structure
III. Moreover, its 1H NMR spectrum revealed two doublets at δ 5.9 (J = 8 Hz) and δ 6.3
(J = 8 Hz) attributable to the pyridazine H-6 and H-5, respectively. It is assumed that
the formation of XIIIa and XIIIb occurred via the intermediacy of the hydroxyimino
derivatives XIIa and XIIb with subsequent cyclization.
Attempts for the preparation of the isoxazolopyridazine XI were carried out by re-
fluxing of Xa in different solvents in presence of dehydrating agents. However, none of
them was fruitful and the starting material was always recovered unchanged.
New pyrano[2,3-d]pyridazine tricarbonitrile derivatives XVIa and XVIb could be pre-
pared by refluxing compounds Ia and Ib with the enaminonitrile XIV in ethanol in
presence of piperidine. Structure XVI was assigned to the product based on elemental
1
analyses, spectral data and analogy with published data7. Thus the H NMR spectrum
of XVIa revealed only two singlets at δ 3.4 and δ 6.9 ppm assignable to the cyano-
methyl group protons and the pyridazine H-6, respectively, beside the aromatic protons
signals at δ 7.3 – 7.7 ppm and the amino group protons signals at δ 7.1 and 8.6 ppm.
Compounds XVIa and XVIb were also the only isolable products obtained when the
pyridazines IIa and IIb were used instead of the hydrazones Ia and Ib in their reaction
with the nitrile XIV.
Accordingly, it could be concluded that the conveniently available cinnamoyl-
acetonitrile hydrazones I are good precursors for the synthesis of the difficulty ac-
cessible pyridazines and their condensed derivatives through simple methods.
EXPERIMENTAL
All melting points were uncorrected. The IR spectra were recorded in KBr with a Pye–Unicam SP-
1
1000 spectrometer; wavenumbers are given in cm−1. The H NMR spectra were run on a Varian EM
390 (90 MHz) and Gemini-200 spectrometers, using tetramethylsilane as an internal reference.
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SCHEME 2
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Nawwar, Swellem, Chabaka:
Chemical shifts are given in ppm (δ-scale), coupling constants (J) in Hz. The mass spectra were re-
corded with a Varian MAT 311 A mass spectrometer (70 eV).
1-Aryl-4-oxo-6-phenyl-1,4,5,6-tetrahydropyridazine-3-carbonitriles (IIa, IIb)
A solution of the hydrazone Ia, Ib (0.01 mol) in tetrahydrofuran (30 ml) in presence of concentrated
sulfuric acid (1 ml) was left overnight at 25 °C. The precipitate formed was collected and crystallized
from the proper solvent6.
3-(Arylhydrazono)cyanomethyl-5-phenyl-4,5-dihydropyrazole3 (IIIa, IIIb)
Compounds Ia, Ib or IIa, IIb (0.01 mol) in tetrahydrofuran (15 ml) were treated each with 99% hy-
drazine hydrate (0.3 g, 0.01 mol) at 25 °C: precipitation occurred immediately after addition and the
solid products were filtered off and crystallized.
Compound IIIa. IR spectrum: 3 400 – 3 200 (2 × NH); 2 200 (C≡N). 1H NMR spectrum: 3.0 dd,
1 H (pyrazoline H-4 axial, J = 15, J = 12); 3.6 dd, 1 H (pyrazoline H-4 equatorial, J = 15, J = 10); 4.9 dd,
1 H (pyrazoline H-5, J = 12, J = 10); 7.0 – 7.7 m, 10 H (aromatic protons); 12.2 s, 4 H (NH); 12.7 brs,
1 H (NH).
1
Compound IIIb. IR spectrum: 3 800 – 3 200 (2 × NH); 2 200 (C≡N). H NMR spectrum: 3.1 dd,
1 H (pyrazoline H-4 axial, J = 15, J = 12); 3.8 dd, 1 H (pyrazoline H-4 equatorial, J = 15, J = 10); 5.1 dd,
1 H (pyrazoline H-5, J = 12, J = 10); 7.0 – 7.7 m, 9 H (aromatic protons); 12.7 brs, 1 H (NH); 15.2 s,
1 H (NH).
1-Aryl-4-hydrazono-6-phenyl-1,4,5,6-tetrahydropyridazine-3-carbonitriles (IVa, IVb)
Compounds IIa, IIb (0.01 mol) in tetrahydrofuran (30 ml) were treated each with 99% hydrazine
hydrate (0.3 g, 0.01 mol) in presence of concentrated sulfuric acid (3 ml) at 25 °C with stirring for
48 h. Hexane (20 ml) was then added to the reaction mixture forming so two layers: the hexane layer
was discarded while the tetrahydrofuran one was partially concentrated and the solid product thus ob-
tained was crystallized.
1
Compound IVa. IR spectrum: 3 400 – 2 860 (NH−NH2 and NH2); 2 220 (C≡N). H NMR spectrum:
2.7 – 3.4 m, 2 H (pyridazine H-5); 5.8 – 6.0 m, 1 H (pyridazine H-6); 7.0 – 7.6 m, 10 H (aromatics);
11.2 brs, 1 H (NH2); 12.1 brs, 1 H (NH).
Compound IVb. IR spectrum: 3 400 – 2 860 (NH−NH2 and NH2); 2 210 (C≡N).
3-Amino-5-aryl-6-phenyl-1H-pyrazolino[4,3-c]pyridazines (Va, Vb)
Compounds IVa, IVb (0.01 mol) were each fused at 220 °C for 6 h in an oil bath. The oil obtained
was triturated with methanol and the solid thus formed was collected and crystallized.
1
Compound Va. IR spectrum: 3 300 – 3 150 (NH2 and NH). H NMR spectrum: 3.8 brs, 1 H (NH);
5.8 m, 1 H (pyrazolinopyridazine H-6); 7.1 – 7.6 m, 11 H (aromatic protons and pyrazolinopyridazine
H-7); 11.3 brs, 1 H (NH).
1
Compound Vb. IR spectrum: 3 300 – 3 150 (NH2 and NH). H NMR spectrum: 4.0 brs, 2 H (NH2);
5.8 m, 1 H (pyrazolinopyridazine H-6); 7.1 – 7.6 m, 10 H (aromatic protons and pyrazolinopyridazine
H-7); 11.5 brs, 1 H (NH).
1,6-Diphenyl-4-(2,4-dinitrophenylhydrazono)-1,4,5,6-tetrahydropyridazine-3-carbonitrile (VI)
A solution of Ia (2.75 g, 0.01 mol) in tetrahydrofuran (30 ml) was treated with 2,4-dinitrophenylhy-
drazine (1.38 g, 0.01 mol) in the presence of concentrated sulfuric acid (1 ml). The reaction mixture
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Pyridazines and their Condensed Derivatives
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was left at 25 °C for 48 h, the precipitated solid product was collected, washed with water thor-
1
oughly and crystallized from dioxane as deep red crystals. IR spectrum: 2 210 (C≡N). H NMR spec-
trum: 2.8 – 3.3 m, 2 H (pyridazine H-5); 6.2 m, 1 H (pyridazine H-6); 7.0 – 7.5 m, 10 H (aromatic
protons); 7.8 d, 1 H (dinitrophenyl H-6, J(6,5) = 9); 8.3 dd, 1 H (dinitrophenyl H-5, J(5,6) = 9, J(5,3)
= 3); 8.8 d 1 H (dinitrophenyl H-3, J(3,5) = 3); 11.1 s, 1 H (NH).
1-Acetyl-3-(phenylhydrazono)cyanomethyl-5-phenyl-4,5-dihydropyrazole (VII)
A solution of IIIa (2.9 g, 0.01 mol) in acetic anhydride (30 ml) was boiled under reflux for 1 h,
cooled, poured into ice water and left overnight. The obtained oil was triturated with acetone to give
a solid product crystallizable from ethanol as yellow crystals. IR spectrum: 3 400 (NH); 2 200
1
(C≡N); 1 650 (C=O). H NMR spectrum: 2.2 s, 3 H (CH3); 3.1 dd, 1 H (pyrazoline H-4 axial); 3.5 dd,
1 H (pyrazoline H-4 equatorial); 5.4 dd, 1 H (pyrazoline H-5); 7.0 – 7.5 m, 10 H (aromatic protons);
11.7 s, 1 H (NH).
1-Acetyl-3-[(N-chloroacetylphenylhydrazono)cyanomethyl]-5-phenyl-4,5-dihydropyrazole (VIII)
A solution of VII (3.3 g, 0.01 mol) in dry benzene (30 ml) in presence of sodium hydride (0.24 g, 0.01
mol) was stirred at 25 °C for 30 min. Chloroacetyl chloride (1.13 g, 0.01 mol) in dry benzene (5 ml)
was added dropwise to the stirred solution over a period of 15 min. Stirring was kept for further 3 h,
then the solvent was evaporated and the oil residue washed with 4 M hydrochloric acid then triturated
with methanol. The resulting solid product was collected and crystallized from ethanol as pale yellow
1
crystals. IR spectrum: 2 210 (C≡N); 1 665 (C=O); 1 650 (C=O). H NMR spectrum: 2.3 s, 3 H (CH3);
2.7 s, 2 H (CH2−Cl); 3.2 dd, 1 H (pyrazoline H-4 axial); 3.5 dd, 1 H (pyrazoline H-4 equatorial); 5.6 dd,
1 H (pyrazoline H-5); 7.0 – 7.6 m, 10 H (aromatic protons).
4-Amino-5-chloro-3-[3-(1-acetyl-5-phenyl)-4,5-dihydropyrazolyl]-1-phenylpyridazine-6-one (IX)
Compound VIII (1.02 g, 0.005 mol) was boiled under reflux in xylene (25 ml) in presence of sodium
hydride (0.12 g, 0.005 mol) for 6 h. The reaction mixture was then partially concentrated, cooled and
the solid formed was dissolved in water then neutralized with dilute hydrochloric acid. The solid
product, thus obtained, was collected and crystallized from dioxane as yellow crystals. IR spectrum:
1
3 300 – 3 200 (NH2); 1 680 (C=O); 1 650 (C=O). H NMR spectrum: 2.2 s, 3 H (CH3); 3.2 dd, 1 H
(pyrazoline H-4 axial); 3.5 dd, 1 H (pyrazoline H-4 equatorial); 4.8 brs, 2 H (NH2); 5.5 dd, 1 H (py-
razoline H-5); 7.1 – 7.8 m, 10 H (aromatic protons).
1-Aryl-3-[(hydroxyimino)aminomethyl]-4-oxo-6-phenyl-1,4,5,6-tetrahydropyridazines (Xa, Xb)
A suspension of Ia, Ib or IIa, IIb (0.01 mol) in dioxane (30 ml) was treated with hydroxylamine
hydrochloride (0.7 g, 0.01 mol) in the presence of pyridine (1 ml). The reaction mixture was refluxed
for 4 h, then left to cool. The precipitated solid product was filtered off and crystallized from the
proper solvent.
1
Compound Xa. IR spectrum: 3 500 (OH); 3 250 – 3 150 (NH2); 1 650 (C=O). H NMR spectrum:
2.8 m, 2 H (pyridazine H-5); 5.9 m, 1 H (pyridazine H-6); 7.1 – 7.6 m, 11 H (10 × aromatic proton and
OH); 8.6 d, 2 H (NH2).
Compound Xb. IR spectrum: 3 500 (OH); 3 200 – 3 180 (NH2); 1 655 (C=O).
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6-Aryl-1-imino-5-phenylisoxazolo[4,3-c]pyridazines (XIIIa, XIIIb)
A solution of Ia, Ib (0.01 mol) in ethanol (25 ml) was treated with hydroxylamine hydrochloride (1.4 g,
0.02 mol) in presence of 10% aqueous sodium hydroxide (10 ml) at 25 °C with stirring for 6 h. The
reaction mixture was neutralized with acetic acid, the solvent was then evaporated and the oil ob-
tained was boiled under reflux in butanol (25 ml) in presence of acetic acid (5 ml) for 40 h. The
reaction mixture was evaporated till dryness, ether (5 ml) was added to the obtained oil followed by
a dropwise addition of petroleum ether (5 ml, b.p. 40 – 60 °C) and the reaction mixture was refrig-
erated overnight. The solid product formed was filtered off and crystallized.
1
Compound XIIIa. IR spectrum: 3 400 – 3 300 (2 × NH); 1 645 (C=N). H NMR spectrum: 5.9 d,
1 H (isoxazolopyridazine H-5); 6.3 d, 1 H (isoxazolopyridazine H-4); 7.1 – 7.7 m, 10 H (aromatic
protons); 11.0 s, 1 H (C=NH); 13.2 s, 1 H (NH).
Compound XIIIb. IR spectrum: 3 400 – 3 300 (2 × NH); 1 650 (C=N).
6-Aryl-2,4-diamino-4-cyanomethyl-5-phenyl-5H-pyrano[2,3-d]pyridazine-3,8-dicarbonitrile (XVIa,
XVIb)
Compounds Ia, Ib or IIa, IIb (0.01 mol) were refluxed each with the nitrile XIV (1.3 g, 0.01 mol) in
butanol (30 ml) in presence of piperidine (1 ml) for 8 h. The reaction mixture was evaporated till
dryness, the oil formed was washed thoroughly with dilute hydrochloric acid and the solid product,
thus obtained, was collected followed by crystallization.
Compound XVIa. IR spectrum: 3 370 – 3 130 (2 × NH2); 2 200 – 2 205 (2 × C≡N). 1H NMR
spectrum: 3.4 s, 2 H (CH2); 6.9 s, 1 H (pyranopyridazine H-5); 7.1 s, 2 H (NH2); 7.3 – 7.7 m, 10 H
(aromatic protons); 8.6 brs, 2 H (NH2).
Compound XVIb. IR spectrum: 3 400 – 3 150 (2 × NH2); 2 220 – 2 200 (2 × C≡N). 1H NMR
spectrum: 3.6 s, 2 H (CH2); 6.9 s, 1 H (pyranopyridazine H-5); 7.2 s, 2 H (NH2); 7.3 – 7.9 m, 9 H
(aromatic protons); 10.2 brs, 2 H (NH2).
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