organic papers o4022 Qadeer et al.  C 11 H 6 O 4 doi:10.1107/S1600536806032399 Acta Cryst. (2006). E62, o4022–o4023 Acta Crystallographica Section E Structure Reports Online ISSN 1600-5368 3H-Furo[3,4-c]isochromene-1,5-dione Ghulam Qadeer, a Nasim Hasan Rama, a * Muhammad Tahir Hussain a and Wai-Yeung Wong b a Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan, and b Department of Chemistry, Hong Kong Baptist University, Waterloo Road, Kowloon Tong, Hong Kong, People’s Republic of China Correspondence e-mail: nasim_hasan_rama@hotmail.com Key indicators Single-crystal X-ray study T = 293 K Mean (C–C) = 0.003 A ˚ R factor = 0.034 wR factor = 0.096 Data-to-parameter ratio = 10.2 For details of how these key indicators were automatically derived from the article, see http://journals.iucr.org/e. Received 14 July 2006 Accepted 15 August 2006 # 2006 International Union of Crystallography All rights reserved The title compound, C 11 H 6 O 4 , is a synthetic isocoumarin and is essentially planar. Comment Isocoumarin is an abundant structural motif in natural products (Barry, 1964). Many constituents of the steadily growing class of known isocoumarins exhibit valuable biolo- gical properties, such as antifungal (Meepagala et al., 2002), antitumor or cytotoxic, anti-inflammatory, anti-allergic (Rossi et al., 2003), and enzyme inhibitory activities (Powers et al. , 2002). Naturally occurring haloisocoumarins and their halo- 3,4-dihydroisocoumarin derivatives are very rare; however, a few examples of naturally occurring chlorine-containing isocoumarins are known (Larsen & Breinholt, 1999). In view of the importance of this class of compounds, the title compound, (I), has been synthesized, and its crystal structure is reported here. The molecular structure of the title compound is shown in Fig. 1. In (I), all bond lengths and angles are within normal ranges (Allen et al., 1987). The five-membered ring is coplanar with the isocoumarin ring system. The bond lengths within the benzene ring lie between 1.375 (3) A ˚ and 1.405 (2) A ˚ . There is no hydrogen bonding below 3.0 A ˚ found in the crystal struc- ture. Experimental A mixture of homophthalic acid (2.0 g, 11 mmol) and chloroacetyl chloride (7.96 g, 5 ml, 46 mmol) was refluxed for 6 h at 473 K with stirring. The reaction mixture was dissolved in ethyl acetate (3  100 ml) and an aqueous solution of sodium carbonate (5%, 2  100 ml) was added in order to remove the unreacted homophthalic acid. The organic layer was separated, concentrated and chromato- graphed on silica gel using petroleum ether (313–353 K fraction) as eluant to afford the title compound (yield 66%, m.p. 404 K). Color- less single crystals suitable for X-ray analysis were obtained by slow evaporation of an ethyl acetate solution.