1-(2-Hydroxy-3,4-dimethoxyphenyl)-2-(4-methoxyphenyl)ethanone

In the title compound, C17H18O5, the pyrogallol group is almost coplanar with the mean plane of the attached carbonyl group [dihedral angle of 1.95 (13)°] and makes a dihedral angle of 56.01 (10)° with the other benzene ring. Of the three methoxy groups, only one is significantly twisted relative to its attached benzene ring [C—O—C—C torsion angles of 4.0 (5), 3.9 (6) and −106.3 (4)°]. Intramolecular O—H⋯O and C—H⋯O hydrogen bonds help to establish the conformation, and the packing is consolidated by C—H⋯O interactions and π–π stacking interactions [centroid–centroid separation = 3.735 (2) Å].

The bond lengths and angles of the title compound, (I), are unexceptional. The carbonyl group is almost coplanar with the pyrogallol fragment with a dihedral angle of 1.95 (13) °. The C16-O4-C4-C5 torsion angle [4.0 (5) °] indicates that the methoxy group is coplanar with the attached phenyl ring (pyrogallol fragment), the same as the methoxy group (O5, C17) attached to the p-methoxyphenyl moiety. However, the C15-O3-C3-C4 torsion angle indicates that the methoxy group is twisted at -106.3 (4) ° with respect to the pyrogallol ring.
The molecule of (I) is stabilized by intramolecular O-H···O and C-H···O hydrogen bonds (Table 1). The six-membered pseudo-ring closed by the former bond is almost planar with mean deviation of 0.010Å and coplanar with the fused C1-C6 benzene ring (Fig. 1). The packing is stabilized by intermolecular C-H···O hydrogen bonds as well as weak π-π interactions with a centroid-to-centroid distance of 3.735 (2)Å.
Experimental 4-Methoxyphenacetyl chloride was prepared by treating 4-methoxyphenacetic acid with thionyl chloride at room temperature for 24 h. The solvent was removed in vacuo. To a mixture of pyrogallol trimethoxyl ether (2 g, 11.9 mmol) and 4-methoxyphenacetyl chloride (2.3 g, 12.2 mmol) in dried carbon disulfide (4 ml) was added anhydrous aluminium chloride (2.8 g) with stirring at room temperature overnight. Then the mixture was heated under reflux for 0.5 h. After removal of the solvent by decantation, the residue was poured into ice-cold diluted hydrochloric acid. The precipitate was suction filtered and crystallized from methanol to furnish light yellow blocks of (I).

Refinement
The H atom bonded to O2 was located in a difference Fourier map and freely refined. All other H atoms were placed in geometrically idealized positions (C-H = 0.93-0.97Å) and refined as riding with U iso = 1.2U eq (C) or 1.5U eq (methyl C).
Figures Fig. 1. The molecular structure of (I) with displacement ellipsoids for the non-hydrogen atoms drawn at the 30% probability level.