Crystal structure of 3,5-dimethoxy-2-[5-(naphthalen-1-yl)-4,5-dihydro-1H-pyrazol-3-yl]phenol

In the title compound, C21H20N2O3, the planes of the benzene ring and the naphthalene ring system are inclined to one another by 70.95°, and by 4.99 (6) and 75.93 (5)°, respectively, to the mean plane of the pyrazoline ring. The latter has an envelope conformation with the methine (CH) C atom as the flap. There is an intramolecular O—H⋯N hydrogen bond that forms an S(6) ring motif. In the crystal, molecules are linked by C—H⋯O hydrogen bonds, forming chains along [100]. The chains are linked via C—H⋯N hydrogen bonds, forming sheets parallel to the ab plane. The sheets are linked by a series of N—H⋯π and C—H⋯π interactions forming a three-dimensional structure.

The molecular structure of the title compound is shown in Fig Table 1).
In the crystal, molecules are linked by C-H···O hydrogen bonds forming chains along [100]. The chains are linked via C-H···N hydrogen bonds forming sheets parallel to the ab plane (Table 1 and Fig. 2). The sheets are linked by a series of N-H···π ( Fig. 3) and C-H···π interactions (Table 1) forming a three-dimensional structure.

S2. Synthesis and crystallization
The starting material chalcone was prepared by the previously reported method (Yong et al. 2013)and the pyrazoline was obtained by cyclization reaction of the chalcone with NH 2 NH 2 , as illustrated in Fig. 4. To a solution of 6-methoxy-2-hydroxyacetophenone (10 mmol, 1.66g) in 50 ml of ethanol was added 2,3-dimethoxy-1-naphthaldehyde (10 mmol, 1.56g) and the temperature was adjusted to around 276-277K in an ice-bath. To the reaction mixture was added 8 ml of 50% (w/v) aqueous KOH solution and the reaction mixture was stirred at room temperature for 20 h. At the end of the reaction, ice water was added to the mixture and it was then acidified with 6N HCl (pH = 3-4). The resulting precipitate was filtered and washed with water and ethanol. The crude solid was purified by recrystallization from ethanol to give the pure chalcone starting material. Excess hydrazine monohydrate (1 ml of 64-65% solution, 13 mmol) was added to a solution of the chalcone compound (5 mmol, 1.52g) in 30 ml anhydrous ethanol, and the solution was refluxed at 360 K for 5 h. The reaction mixture was cooled to room temperature to yield a solid that was then filtered. The crude solids were purified by recrystallization from ethanol to afford the pure pyrazoline title compound as yellow needle-like crystals

S3. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The NH and OH H atoms were located in a difference Fourier map and freely refined. The C-bound H atoms were placed in calculated positions and included in the refinement in a riding-model approximation: C-H = 0.95-1.00 Å with U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (C) for other H atoms.

Figure 1
The molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 30% probability level.

Figure 2
A view along the c axis of the crystal packing of the title compound. The hydrogen bonds are shown as dashed lines (see Table 1).

Figure 3
A view of the inversion dimers formed by a pair of N-H···π interactions (dashed lines; see Table 1), in the crystal structure of the title compound.

Figure 4
Synthetic scheme for the preparation of the title pyrazoline compound.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.