Acta Crystallographica Section C
Crystal Structure
Communications
ISSN 0108-2701
5-Amino-6-phenyl-1,6-dihydro-
pyridazin-3(2H)-one
a
a
Figure 1
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Hector Novoa de Armas, *² Norbert M. Blaton,
Oswald M. Peeters,a Camiel J. De Ranter,a Beatriz Pita,b
A plot of (I) showing the atomic numbering scheme. Displacement
ellipsoids are drawn at 50% probability level, and H atoms are shown as
spheres of arbitrary radii.
b
b
c
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Eddy Sotelo, Enrique RavinÄa and Margarita Suarez
aLaboratorium voor Analytische Chemie en Medicinale Fysicochemie, Faculteit
Farmaceutische Wetenschappen, Katholieke Universiteit Leuven, Van Evenstraat 4,
b
we used this compound as an intermediate in the synthesis of
pyrido[2,3-d]pyridazines (Pita et al., 2000).
There are no unusual bond distances and angles in (I), and
they are in the range of calculated values using the AM1
method in related structures (Estevez et al., 1998). The bond
lengths in the pyridazinone ring range from 1.304 (2) to
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B-3000 Leuven, Belgium, Departamento de Quõmica Organica, Laboratorio de
Quimica Medicinal, Facultad de Farmacia, Universidad de Santiago de Compostela,
c
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Santiago de Compostela, 15706 Galicia, Spain, and Departamento de Quõmica
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Organica, Laboratorio de Sõntesis Organica, Universidad de La Habana, Apartado
10400, La Habana, Cuba
Correspondence e-mail: hector.novoa@farm.kuleuven.ac.be
Ê
1.450 (3) A. The torsion angle between the pyridazinone and
Received 13 September 1999
Accepted 24 November 1999
the phenyl ring, found using the quantum chemical AM1
method in MOPAC (Stewart, 1990) for the lower energy
conformations, is in the range 40±140ꢀ, with a heat of forma-
In the title compound, C10H9N3O, the pyridazinone moiety is
essentially planar and forms a dihedral angle of 49.5 (1)ꢀ with
the phenyl substituent. The molecular packing is stabilized by
van der Waals interactions and hydrogen bonds.
1
tion of 38.30 kcal mol (1 kcal = 4.184 kJ). In the crystal
structure this angle is 51.3 (3)ꢀ, which corresponds to the
minimum in the energy calculations. The calculated favoured
conformation of the enol form corresponds to torsion angles
in the same range (40±140ꢀ) and a heat of formation of
34.20 kcal mol 1, which shows that this enol is the predomi-
nant form at equilibrium. This is contrary to the fact that in the
crystal the molecule is present in the amide form, which
corresponds to a higher heat of formation. The dihedral angle
between the respective least-squares planes of the pyridazi-
none ring and the phenyl ring is 49.5 (1)ꢀ. The mean Csp2Ð
Comment
It is known that 6-aryl-3(2H)-pyridazinones and their 4,5-di-
hydro derivatives display several pharmacological activities,
all of them related to cardiotonics, such as reduction of blood
pressure, inhibition of platelet aggregation, positive inotropic
activity, and others (Robertson et al., 1986). Likewise, 6-aryl-
pyridazinones with nitro and acyl substituents at the 4- and 5-
positions show good antiaggregating properties (Schudt et al.,
1991). We have previously reported the synthesis of 5-
aminomethyl-6-aryl-4,5-dihydropyridazinones and 6-aryl-5-
aminomethyl-3(2H)-pyridazinones (RavinÄa et al., 1990). Some
of these compounds show a good in vitro inhibitory activity on
ADP-induced rat platelet aggregation. As a continuation of
this previous report on the chemistry and pharmacology of
this class of compounds, we carried out the crystal structure
2
Ê
Csp bond length within the phenyl ring is 1.382 (1) A. A view
of (I) can be seen in Fig. 1.
The N3 atom of the amine and the N1 atom of the amide
group in the pyridazinone ring are involved in two inter-
molecular hydrogen bonds with a neighbouring O1, forming
an in®nite two-dimensional network in the plane [001].
Experimental
A
suspension of 5-bromo-6-phenyl-3(2H)-pyridazinone (0.5 g,
1.9 mmol), ammonium chloride (0.3 g, 5.6 mmol) and ammonium
hydroxide (50 ml) was heated at 458 K at pressure of 374 psi (1 psi '
6.895 kPa) for 3 h in a Parr reactor. The mixture was evaporated in
vacuo and washed with ammonium hydroxide, and the solid obtained,
(I), was recrystallized from ethanol (yield 70%; m.p. 517 K). Spec-
1
troscopic analysis: IR (KBr), cm 1: 3480±3425 (NH), 1670 (CO); H
NMR (DMSO-ꢀ6, p.p.m.): ꢀ 12.12 (s, 1H, NH, deuterium oxide
exchangeable), 7.50±7.43 (m, 5H, aromatics), 5.71 (s, 1H, CHÐCO),
5.96 (s, 2H, NH2); 13C NMR (p.p.m.): ꢀ 162.5 (C3), 99.1 (C4), 149.2
(C5), 140.1 (C6), 134.4 (C10), 129.1 (C20, C60), 128.8 (C30, C50), 129.1
(C40); analysis, calculated: C 64.16, H 4.85, N 22.45%; found: C 64.20,
H 4.78, N 22.43%.
determination of 5-amino-6-phenyl-1,6-dihydropyridazin-
3(2H)-one, (I). This enamine-like compound can be employed
in the synthesis of hetero-condensed pyridazinones. Recently,
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² On leave from: Centro de Quõmica Farmaceutica, Departamento de Analisis,
Apartado 16042, La Habana, Cuba.
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Acta Cryst. (2000). C56, 345±346
# 2000 International Union of Crystallography
Printed in Great Britain ± all rights reserved 345
Novoa De Armas, Hector
