3-(3-Chlorobenzyl)-1H-isochromen-1-one

The asymmetric unit of the title compound, C16H11ClO2, a chemically synthesized isocoumarin, contains three independent molecules. The benzopyran and benzene rings are approximately perpendicular to each other, forming dihedral angles ranging from 83.08 (14) to 87.43 (11)°. In the crystal structure, molecules are linked by intermolecular C—H⋯O hydrogen-bonding interactions, forming chains running parallel to the a axis.

The asymmetric unit of the title compound, C 16 H 11 ClO 2 , a chemically synthesized isocoumarin, contains three independent molecules. The benzopyran and benzene rings are approximately perpendicular to each other, forming dihedral angles ranging from 83.08 (14) to 87.43 (11) . In the crystal structure, molecules are linked by intermolecular C-HÁ Á ÁO hydrogen-bonding interactions, forming chains running parallel to the a axis.

Comment
The isocoumarin nucleus is an abundant structural motif in natural products (Barry, 1964). Many constituents of the steadily growing class of known isocoumarins exhibit valuable biological properties such as antifungal (Sturtz et al., 2002), antitumor or cytotoxic, anti-inflammatory, anti-allergic (Rossi et al., 2003 and enzyme inhibitory activity (Powers et al.,2002).
Naturally occurring halo-isocoumarins and their halogeno-3,4-dihydroiscoumarin derivatives are very rare. However, a few examples of naturally occurring chlorine containing isocoumarins are known (Thomas & Jens, 1999). In view of the importance of this class of compounds, the title compound, an isocoumarine derivative containing a 3-chlorobenzyl substituent, has been synthesized and its crystal structure is reported here.
The asymmetric unit of the title compound contains three crystallographically independent molecules of similar geometry ( Fig.1). The molecules are not planar, the dihedral angles formed by the benzopyran ring with the corresponding benzene ring being 83.08 (14), 87.43 (11) and 84.25 (14)° for the molecules containing Cl11, Cl21 and Cl31, respectively.
The bond lengths (Allen et al., 1987) and angles are within normal ranges and comparable with those reported for 3-(2chlorobenzyl)isocoumarin (Abid et al., 2006). In the crystal packing, molecules are linked by intermolecular C-H···O hydrogen bonds (Table 1) into chains running parallel to the a axis (Fig. 2).

Experimental
A mixture of 2-(3-chlorophenyl)acetic acid (4.76 g, 28 mmol) and thionyl chloride (2.94 ml, 34 mmol) was heated for 30 min in the presence of a few drops of DMF under reflux at 343 K to give 2-(3-chlorophenyl)acetyl chloride. Completion of the reaction was indicated by the disappearance of gas evolution. The removal of excess thionyl chloride was carried out under reduced pressure to afford 2-(3-chlorophenyl)acetyl chloride. Homophthalic acid (1.3 g, 7.2 mmol) was then added and the solution was refluxed for 6 hrs at 473 K with stirring. The reaction mixture was extracted with ethyl acetate (3 times 100 ml), and an aqueous solution of sodium carbonate (5%, 200 ml) was added to remove the unreacted homophthalic acid. The organic layer was separated, concentrated and chromatographed on silica gel using petroleum ether (313-353 K fractions) as eluent to afford the title compound (yield 62%; m.p. 350-351 K). Colourless single crystals suitable for X-ray analysis were obtained by slow evaporation of an ethyl acetate solution.

Refinement
H atoms were positioned geometrically with C-H = 0.93-0.97Å and constrained to ride on their parent atoms, with U iso (H) = 1.2 U eq (C). The poor diffraction quality of the crystal may account for the high R int , weighted and unweighted R factors. Fig. 1. The asymmetric unit of the title compound, with displacement ellipsoids drawn at the 50% probability level.