Crystal structure of (Z)-3-benzyloxy-6-[(2-hydroxyanilino)methylidene]cyclohexa-2,4-dien-1-one

In the title compound, C20H17NO3, the methylidenecyclohexa-2,4-dienone moiety is approximately planar [maximum deviation = 0.0615 (10) Å] and is oriented at diherdral angles of 69.60 (7) and 1.69 (9)° to the phenyl and hydroxybenzene rings, respectively. The amino group links with the carbonyl O atom via an intramolecular N—H⋯O hydrogen bond, forming an S(6) ring motif. In the crystal, the molecules are linked by O—H⋯O hydrogen bonds and weak C—H⋯O and C—H⋯π interactions, forming a three-dimensional supramolecular architecture.


S1. Comment
Azomethine compounds are extensively incoporated in many pharmaceutical and food industry applications (Prakash & Adhikari, 2011). Elimination of excess drugs from the bloodstream or body is an essential process to protect against potential toxicity. In most cases the more hydrophilic drugs/pharmacophores are the more they are readily excreted by the kidneys in urine (Lin & Lu, 1997). The existence of conjugated double bonds and more hydroxylic groups in bioactive molecules increases not only their hydrophilicity but also the rate of their membrane absorption. Based on such facts we herein report the crystal structure of a potential bioactive hydrophilic azomethine derivative.
A view of the molecular structure of (I) with numbering Scheme is shown in Fig. 1. In the molecule, the methylenecyclohexa-2,4-dienone moiety is approximately planar [maximum deviation = 0.0615 (10) Å] and its mean plane is oriented with respect to the terminal benzene rings at 69.60 (7) and 1.69 (9)°, respectively. The amino group links with the carbonyl O atom via an intramolecular N-H···O hydrogen bond, forming an S(6) ring motif. In the crystal, the molecules are linked by the intermolecular O-H···O hydrogen bond, weak C-H···O and C-H···π interactions to form the three dimensional supramolecular architecture.
To this a few drops of conc. HCL was added as a catalyst and refluxed for 4 h. After cooling the solution, After stirring at 80°C for 45 min the formed precipitate was filtered off and washed with ice ether and ethyl acetate to give pure Schiff base as an Orange solid in an 35% yield. The crude product was dissolved in ethyl acetate and two spoons of activated charcoal were added. the mixture was filtered and the product was crystallized from an ethyl acetate solution.

S3. Refinement
All hydrogen atoms were fixed geometrically and treated as riding with C-H = 0.93-0.97 Å and N-H = 0.86 Å, U iso (H) = 1.2U eq (C,N).  View of the molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
Partial view along the b axis of the crystal packing of the title compound, showing the hydrogen bonds as dashed lines (see Table 1 for details).

(Z)-3-Benzyloxy-6-[(2-hydroxyanilino)methylidene]cyclohexa-2,4-dien-1-one
Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles 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. Hydrogen-bond geometry (Å, º) Cg1 is the centroid of the C15-C20 ring. Symmetry codes: (i) −x, y−1/2, −z+1/2; (viii) −x+1, y−1/2, −z+1/2; (ix) −x, −y+1, −z.