4-[(4-Benzyloxybenzylidene)amino]-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one

In the title molecule, C25H23N3O2, two terminal phenyl rings are twisted by 50.20 (6) and 71.26 (5)° from the mean plane (r.m.s. deviation = 0.032 Å) of the central benzylidene–amino–pyrazolone fragment. The N atoms of the pyrazole ring have a pyramidal environment, the sums of the valence angles around them being 353.5 (2) and 347.3 (2)°. The crystal structure is stabilized by C—H⋯O interactions.

In the title molecule, C 25 H 23 N 3 O 2 , two terminal phenyl rings are twisted by 50.20 (6) and 71.26 (5) from the mean plane (r.m.s. deviation = 0.032 Å ) of the central benzylidene-aminopyrazolone fragment. The N atoms of the pyrazole ring have a pyramidal environment, the sums of the valence angles around them being 353.5 (2) and 347.3 (2) . The crystal structure is stabilized by C-HÁ Á ÁO interactions.

Related literature
Related crystal structures have been described by Shi (2005), Jun (2005), Zhen et al. (2006), Liu et al. (2006), Diao & Chen (2006), Duan et al. (2006), Hu (2006) and Zhang et al. (2006).  Table 1 Hydrogen-bond geometry (Å , ).  Pyrazolone, as a prominent structural motif, is found in numerous pharmaceutically active compounds. Due to the easy preparation and rich biological activity, pyrazolone framework plays an essential role and represents an interesting template for combinatorial and medicinal chemistry. Indeed, pyrazolone based derivatives have shown several biological activities such as analgesic, anti-inflammatory, antipyretic, antiarrhythmic, antifungal, muscle relaxing, psychoanaleptic, anticonvulsant, enzyme inhibiting, antidiabetic and antibacterial activities. So, the chemistry of pyrazolone and its derivatives is particularly interesting because of their potential application in medicinal chemistry. Here we present the results of the X-ray structure determination of the title compound, 1.

Experimental
Quite recently, the crystal structures of a series of similar compounds, with substituted rings C and D (cf. Compound 1, without additional substituents on the phenyl rings, might be regarded as the reference molecule. It has almost perfectly coplanar central part, consisting of two rings B and C (pyrazolone and phenyl) and the linking C-N=C -C chain (maximum deviation from the least-squares plane is 0.070 (1) Å). The dihedral angle between the planes of the two rings B and C is only 1.42 (13)°, and is significantly smaller than in the other similar molecules (6.21 (10) In the pyrazolone ring, the N atoms of the pyrazole ring have pyramidal environment, sums of the valence angles around them are 353.5° for N1 and 347.3° for N2. The bond lengths pattern within this ring suggests significant delocalization and is also typical for these compounds, in contrast, the bond N41-C42 (1.276 (2) Å) has an obvious double-bond character.
In the crystal structure relatively short and linear C16-H16···O49 i hydrogen bonds join molecules into centrosymmetric dimers; these dimers, in turn, by means of other, still weaker C-H···O contacts expand in two dimensions (Table 1, Fig. 2).

Refinement
Hydrogen atoms were found in difference Fourier maps and isotropically refined.

Figure 1
The molecular structure of 1 showing the atom labelling scheme and ring labels (cf. Comment). Displacement ellipsoids are drawn at the 50% probability level, hydrogen atoms are depicted as spheres with arbitrary radii.

Figure 2
A portion of the crystal packing viewed along [010] direction; C-H···O hydrogen bonds (cf.  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.68 e Å −3 Δρ min = −0.22 e Å −3 Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.