[CH2:1]1[CH:4]2[CH2:5][C:6]3[CH:7]=[CH:8][CH:9]=[CH:10][C:11]=3[CH:3]2[C:2]1=[O:12].[OH:13]O.[Na]>C(O)(=O)C.O>[O:13]1[C:2](=[O:12])[CH2:1][CH:4]2[CH2:5][CH:6]3[C:11]([CH:10]=[CH:9][CH:8]=[CH:7]3)=[C:3]12A solution of 1,2a,7,7a-tetrahydro-2H-Cyclobut[a]inden-2-one (Example I4, 0.377 mg, 2.383 mmol) in acetic acid (5 mL) and water (0.5 mL) was cooled at 0° C. and hydrogen peroxide (30% in water, 0.810 mL, 7.14 mmol) was added. The solution as stirred for 3 h at 0° C. and the reaction mixture was poured into saturated solution of sodium hydrogenocarbonate. The solution was extracted with ethyl acetate and the combined organic layers were washed with brine, dried and concentrated. The residue was purified by flash chromatography eluting with cyclohexane and ethyl acetate (4/1) to give rac-Tetrahydroindeno[1,2-b]furan-2-one (Colourless oil, 383 mg, 92%), that solidified upon cooling (data match with litt data, CAS 4471-33-4). C11H10O2; MW: 174.20; LCMS (method A) RT 1.32 min; ES: 175 (60%, MH+), 129 (100%); IR: 1769 cm−1; 1H NMR (400 MHz, CDCl3) δ 7.50 (1H, d), 7.25-7.39 (4H, m), 5.91 (1H, d), 3.28-3.45 (2H, m), 2.86-2.97 (2H, m), 2.41 (1H, dd) ppm.
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