Crystal structure of (Z)-3-benzyloxy-6-[(2-hydroxy-5-methylanilino)methylidene]cyclohexa-2,4-dien-1-one

In the title Schiff base compound, C21H19NO3, the conformation about the C=C bond is Z. The N—H group and carbonyl O atom form an intramolecular N—H⋯O hydrogen bond with an S(6) ring motif. The benzyloxy ring and the 2-hydroxy-5-methylphenyl ring are inclined to the central six-membered ring by 13.68 (9) and 9.13 (8)°, respectively, and to one another by 21.95 (9)°. In the crystal, molecules are linked by O—H⋯O hydrogen bonds, forming helical chains along [010].

To this a few drops of conc. HCL was added as a catalyst and the mixture was refluxed for 12 h. After cooling the solution to 80°C it was stirred for 45 min the a precipitate formed. It was filtered off and washed with ice cold ethyl acetate to give the pure title Schiff base compound as an orange solid (yield 35%). This crude product was dissolved in ethyl acetate and two spoons of activated charcoal were added. The mixture was filtered over celiteµ000174 and the product was crystallized from ethyl acetate. The compound was very difficult to crystalize and only after several attempts over a period of four months were crystals suitable for X-ray diffraction analysis finally obtained.

S2. Refinement
The OH and NH H atoms, and the methine H atom were located in a difference Fourier map and freely refined. The Cbound H atoms were fixed geometrically and treated as riding atoms: C-H = 0.93 Å (aromatic) and 0.97 Å (methylene) with U iso (H) = 1.2U eq (C).
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Figure 1
View of the molecular structure of the title molecule, 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). 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.