Crystal structure of (E)-4-hydroxy-3-{1-[(4-hydroxyphenyl)imino]ethyl}-6-methyl-2H-pyran-2-one

In the title Schiff base, C14H13NO4, which adopts the phenol–imine tautomeric form, the dihedral angle between the planes of the benzene and heterocyclic (r.m.s. deviation = 0.037 Å) rings is 53.31 (11)°. An intramolecular O—H⋯N hydrogen bond closes an S(6) ring. In the crystal, molecules are linked by O—H⋯O hydrogen bonds to generate C(11) chains propagating in the [010] direction. A weak C—H⋯O link is also observed, leading to the formation of R 5 5(32) rings extending parallel to the (101) plane.

Depending on the tautomers, two types of intra-molecular hydrogen bonds are possible: O-H···N in benzenoid and N-H···O in quinoid tautomers.
As part of our ongoing studies of Schiff bases (Djedouani et al., 2007(Djedouani et al., , 2008, we now describe the synthesis and the structure of the title compound, which takes the form phenol-imine and complete a six-membered pseudocycle via an intramolecular O-H····O hydrogen bond. The dehydroacetic acid ring and phenyl ring are almost planer with r.m.s deviation for the mean plane are 0.0260 and 0.0027 respectively. The dihedral angle between the two rings is 53.30 (0.05) °. The two torsional angles τ1 (N1-C5-C14-C4) and τ2 (C5-N1-C1-C6) defining the confirmation of the molecule.

S2. Experimental
Compound (I) was prepared by refluxing a mixture of a solution containing dehydroacetic acid (0.01 mmol) and para-4aminophenol (0.01 mmol) in ethanol (40 ml). The reaction mixture was stirred for 2 h under reflux and left to cool.
Yellow crystals grew after a few days. The methyl H atoms were constrained to an ideal geometry (C-H = 0.96 Å) with U iso (H) = 1.2Ueq(C), but were allowed to rotate freely about the C-C bonds.

Figure 1
The structure of the title compound in 50% probability ellipsoids.

Figure 2
Part of the crystal structure of (I), showing the formation of S(6) rings with dashed red lines. C-H···O and O-H···O hydrogen bonds are shown as blue dashed lines.