Phthalide → Indeno(1,2-c)isochromene-5,11-dione

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Sodium methoxide (40 mL of a 4 M methanolic solution) was added to a solution of 2-carboxybenzaldehyde 1d (1.000 g, 7.455 mmol) and phthalide 2d (1.119 g, 7.455 mmol) in ethyl acetate (20 mL). The solution was heated at 65° C. for 18 h, concentrated, and acidified with coned HCl. The resulting mixture was diluted with benzene (125 mL), TsOH (100 mg) was added, and the solution was heated for 7 h at reflux in a flask affixed with a Dean-Stark trap. The solution was cooled to room temperature, concentrated, diluted with CHCl3 (150 mL), and washed with sat NaHCO3 (3×50 mL) and sat NaCl (50 mL). The organic layer was dried over sodium sulfate and concentrated to provide indenobenzopyran 4d as an orange solid (1.583 g, 86%): mp 258-259° C. (published mp 257° C.). 1H NMR (CDCl3) δ 8.40 (d, J=8.56 Hz, 1H), 8.32 (d, J=7.93 Hz, 1H), 7.84-7.79 (m, 1H), 7.61-7.39 (m, 5H). Additional details regarding the synthesis of compound 8 are found in Pailer et al., Monatsh Chem., 92:1037-47 (1961), the synthetic disclosure of which is incorporated herein by reference.

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