5-Chloro-6-hydroxy-7,8-dimethylchroman-2-one

In the title molecule, C11H11ClO3, the fused pyran ring adopts a half-chair conformation. In the crystal, intermolecular O—H⋯O hydrogen bonds link molecules into chains along [100]. These chains are interconnected by weak intermolecular C—H⋯O contacts which generate R 2 2(8) ring motifs, forming sheets parallel to (001). Tetragonal symmetry generates an equivalent motif along b. Furthermore, the sheets are linked along the c axis by offset π–π stacking interactions involving the benzene rings of adjacent molecules [with centroid–centroid distances of 3.839 (2) Å], together with an additional weak C—H⋯O hydrogen bond, resulting in an overall three-dimensional network.

In the title molecule, C 11 H 11 ClO 3 , the fused pyran ring adopts a half-chair conformation. In the crystal, intermolecular O-HÁ Á ÁO hydrogen bonds link molecules into chains along [100]. These chains are interconnected by weak intermolecular C-HÁ Á ÁO contacts which generate R 2 2 (8) ring motifs, forming sheets parallel to (001). Tetragonal symmetry generates an equivalent motif along b. Furthermore, the sheets are linked along the c axis by offsetstacking interactions involving the benzene rings of adjacent molecules [with centroidcentroid distances of 3.839 (2) Å ], together with an additional weak C-HÁ Á ÁO hydrogen bond, resulting in an overall threedimensional network.
Data collection: APEX2 (   Compound (I) , Fig 1, consists of a chromanone unit with an OH substituent at C4, a chloro substituent at C5 and methyl substituents on C2 and C3. The fused C1/C6-C9/O1 ring is in a half-chair conformation. Bond distances (Allen et al., 1987) and angles are normal and similar to those in closely related structures (Budzianowski & Katrusiak, 2002;Goswami et al., 2011).

Experimental
The title compound was synthesized in three steps. In the first step trimethyl-p-hydroquinone (Fieser & Ardao, 1956) (15.2 g, 100 mmol) was oxidized using sodium dichromate (10.8 g, 41 mmol) in acetic acid (50 ml). The product was characterized using NMR spectroscopy and the data were consistent with reported data of trimethyl-p-benzoquinone. The second step (chlorination) is an alternative to the existing literature (Bishop et al., 1963). Trimethyl-p-benzoquinone (10 g, 67 mmol) was added to conc. hydrochloric acid (100 ml) with vigorous stirring. The resulting suspension was heated to reflux for 3 hr.
After dilution with water the solid was filtered out and re-dissolved in aqueous acetic acid. Aqueous sodium dichromate (10 g, 38 mmol) was added in portions. After the mixture had stood for 15 min, a yellow solid was precipitated by dilution with water. Crystallization from ethanol-water solution gave a yellow material, m.p. 337-338K; (lit. m.p. 337-338K). In the final step, a solution of methyl malonate (5.7 g, 43 mmol) in dry MeOH (25 ml) was refluxed for one hour with finely powdered MgOMe (3.85 g, 70 mmol). A solution of chlorotrimethyl-p-quinone (4 g, 21 mmol) in dry MeOH (25 ml) was added dropwise to the refluxing solution and reflux continued for 13 hr. The solid was removed from the cooled mixture, washed with ether and carefully mixed with HCl (10%, 50 ml) and stirred at 283K to remove impurities. The yellow solid product (3 g) was filtered out and dissolved in acetone and stirred with dil. hydrochloric acid (100 ml). The resulting white suspension was then refluxed for 5 hr. The solution was cooled and extracted with ether (3 × 30 mL) and the combined organic extracts washed with brine, dried (MgSO 4 ) and evaporated. To the crude residue in toluene (60 ml), 4-methylbenzenesulfonic acid (0.47 g, 27 mmol) was added with stirring, and the mixture then refluxed. After 12 hr, the nearly colourless solution was cooled to room temp. and extracted with EtOAc (3 × 30 ml). The organic extract was washed with sat. aqueous NaHCO 3 and the aqueous layer back-extracted once with EtOAc (30 ml). The combined organic extracts were washed with brine and dried over MgSO 4 . X-ray quality crystals of the title compound, 5-chloro-6-hydroxy-7,8-dimethylchroman-2-one were  12.6, 22.0, 28.6,115.1, 117.8, 123.8, 125.0, 143.8, 145.9, 165.3.

Refinement
The OH hydrogen atom was located in a difference Fourier map and refined freely with U iso = 1.2U eq (O). Methyl and methylene H-atoms were refined using a riding model with d(C-H) = 0.98 Å, U iso =1.5U eq (C) for methyl and 0.99 Å, U iso =1.2U eq (C) for methylene. Fig. 1. The molecular structure of (I) showing ellipsoids drawn at the 50% probability level.