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Molecules 2011, 16(1), 915-932; doi:10.3390/molecules16010915
Article

X-Ray Supramolecular Structure, NMR Spectroscopy and Synthesis of 3-Methyl-1-phenyl-1H-chromeno[4,3-c]pyrazol-4-ones Formed by the Unexpected Cyclization of 3-[1-(Phenyl-hydrazono)ethyl]-chromen-2-ones

1
,
2, 1, 2, 1 and 2,*
1 Unidad Profesional Interdisciplinaria de Biotecnología del Instituto Politécnico Nacional, Av. Acueducto s/n, Barrio la Laguna Ticomán 07340, México D. F., Mexico 2 Facultad de Ciencias Químicas, Universidad de Colima, km 9 Carretera Coquimatlán-Colima, Coquimatlán Colima 28400, Mexico
* Author to whom correspondence should be addressed.
Received: 16 December 2010 / Revised: 8 January 2011 / Accepted: 18 January 2011 / Published: 21 January 2011
(This article belongs to the Section Molecular Diversity)
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Abstract

The molecular structures of nine 3-methyl-1-phenyl-1H-chromeno[4,3-c]pyrazol-4-one isomers, obtained by the oxidative cyclization of the corresponding 1-phenylhydrazono chromen-2-ones with copper acetate as catalyst, are reported. The molecular and supramolecular structures of the 8-chloro, 8-bromo- and 8-nitro isomers 2b-d, were established by X-ray diffraction. The halogenated isomers 2b and 2c are isomorphs, they crystallize as a triclinic system, space group P-1 with two molecules in the asymmetric unit. Compound 2d crystallizes as a monoclinic system, space group P21/m with two molecules in the unit cell. The 1-phenyl ring [Cg(4)] is almost perpendicularly positioned to the chromene-pyrazole ring system. This conformation is in agreement with the anisotropic NMR shielding effect exerted by the phenyl ring over H-9 in solution. The supramolecular architecture is almost controlled by C―H···A (A = O, p) and face to face p-stacking interactions. The observed p-stacking trend between chromene and pyrazole rings is given by the overlapping between the best donor and acceptor rings in each compound.
Keywords: oxidative cyclization; benzopyrano-arylhydrazone; benzopyrano-pyrazolone; pi-stacking oxidative cyclization; benzopyrano-arylhydrazone; benzopyrano-pyrazolone; pi-stacking
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Padilla-Martinez, I.I.; Flores-Larios, I.Y.; García-Baez, E.V.; Gonzalez, J.; Cruz, A.; Martínez-Martinez, F.J. X-Ray Supramolecular Structure, NMR Spectroscopy and Synthesis of 3-Methyl-1-phenyl-1H-chromeno[4,3-c]pyrazol-4-ones Formed by the Unexpected Cyclization of 3-[1-(Phenyl-hydrazono)ethyl]-chromen-2-ones. Molecules 2011, 16, 915-932.

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