Crystal structure of (3,5-dibromo-2-hydroxyphenyl){1-[(naphthalen-1-yl)carbonyl]-1H-pyrazol-4-yl}methanone

In the title compound, C21H12Br2N2O3, a 1,4-diaroyl pyrazole derivative, the dihedral angles between the naphthalene ring system and the pyrazole ring, the pyrazole and benzene rings, and the naphthalene ring system and benzene ring are 50.0 (2), 51.1 (2) and 1.34 (16)°, respectively. The phenolic proton forms an intramolecular O—H⋯O hydrogen bond with the adjacent carbonyl O atom. In the crystal, molecules are linked by C—H⋯O hydrogen bonds, forming inversion dimers. The dimers are linked by C—H⋯Br hydrogen bonds, forming double stranded chains along [01-1]. The chains are linked by π–π interactions between the pyrazole rings and between the naphthalene and benzene rings [centroid–centroid distances = 3.592 (4) and 3.632 (4) Å, respectively].

The reaction of 6,8-dibromo-3-formylchromone (Ishikawa, 2014) with 1-naphthoylhydrazide in ethanol gave white solids, and orange crystals were obtained from an acetonitrile/ethanol solution of the white solids ( Fig. 1). The crystallographic analysis revealed that the structure of the orange crystals is a 1,4-diaroyl pyrazole, as shown in Fig. 2, which should be thermodynamically more stable than that of the white solids. The dihedral angles between the naphthalene and pyrazole rings, the pyrazole and benzene rings and the naphthalene and benzene rings are 50.0 (2), 51.1 (2) and 1.34 (16)°, respectively. The phenolic proton forms an intramolecular O-H···O hydrogen bond with the adjacent carbonyl O2 atom. In the crystal, the molecules are linked through stacking interactions between the pyrazole rings and the naphthalene and benzene rings [centroid-centroid distances = 3.553 (4) and 3.632 (4) Å, respectively, i: -x + 2, -y, -z + 1], and are further connected through intermolecular C-H···O hydrogen bonds, as shown in Fig. 3. A significant short contact around the bromine atoms is not observed.
The driving force of the intramolecular cyclization ( Fig. 1) should be a resonance energy gain, resulting from the extension of the conjugated system across the entire molecule. The intramolecular cyclization is not observed for the chromone derivatives with electron-donating substituents (Ishikawa & Watanabe, 2014a,b,c,d), and thus the activation energy for the chromone derivative with the electron-withdrawing substituents should be lower than that for ones with electron-donating substituents.

Figure 1
Reaction scheme for the title compound.

Figure 2
The molecular structure of the title compound, with displacement ellipsoids drawn at the 50% probability level.
Hydrogen atoms are shown as small spheres of arbitrary radius.

Figure 3
A crystal packing view of the title compound. Intramolecular O-H···O and intermolecular C-H···O hydrogen bonds are represented by dashed lines.