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

In the title compound, C20H18N2O2, the central pyrazoline ring has an envelope conformation with the atom substituted by the naphthalene ring as the flap. It bridges a benzene ring and a naphthalene ring system which are almost normal to one another, making a dihedral angle of 82.03 (6) °. There is an intramolecular O—H⋯N hydrogen bond forming an S(6) ring motif. In the crystal, molecules are linked by pairs of N—H⋯π interactions, forming inversion dimers. There are also C—H⋯π interactions present and the dimers are linked via C—H⋯O hydrogen bonds, forming ribbons propagating along the a-axis direction.


S1. Introduction
Pyrazolines have been reported to show a wide range of biological activities: They have been reported to be effective as Alzheimer drugs (Neudorfer et al., 2014), and as having anti-inflammatory (Viveka et al., 2015) and antitumor properties (Congiu et al., 2010). The title pyrazoline derivative was synthesized in continuation of our research program (Hwang et al. 2013), and we report herein on its crystal structure.
The molecular structure of the title compound is shown in Fig In the crystal, molecules are linked by pairs of N-H···π interactions forming inversion dimers ( Fig. 2 and Table 1).
There are also C-H···π interactions present and the dimers are linked via C-H···O hydrogen bonds forming ribbons propagating along the a axis direction. (Table 1).
An example of intermolecular N-H···π interaction in pyrazoline system was reported in a recent publication (Naveen et al., 2015). Examples of pyrazoline structures have been also published (Zhu et al., 2013;Patel et al., 2013).

S2. Experimental
To a solution of 6-methoxy-2-hydroxyacetophenone (10 mmol, 1.66 g) in 40 ml of ethanol was added 1-naphthaldehyde (10 mmol, 1.56 g) and the temperature was adjusted to around 276-277 K in an ice-bath. To the reaction mixture was added 10 ml of 50% (w/v) aqueous KOH solution and the reaction mixture was stirred at room temperature for 24 h. At the end of the reaction, ice water was added to the mixture and it was 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 pure chalcone. Excess hydrazine monohydrate (1 ml of 64-65% solution, 13 mmol) was added to a solution of the chalcone compound (5 mmol, 1.52 g) 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 title compound as yellow needles (m.p.: 429-430 K; yield: 56%).

S2.1. Refinement
Crystal data, data collection and structure refinement details are summarized in ride on their parent atoms: 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. The intramolecular O-H···N hydrogen bond is shown as a dashed line (see Table 1).

Figure 2
Part of the crystal structure of the title compound, showing the intramolecular O-H···N hydrogen bond and the intermolecular N-H···π interactions, as dashed lines (see Table 1). H atoms not involved in these interactions have been omitted for clarity.  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.