Reaction Steps
Fluorescein (40 g, 120.5 mmol) was dissolved in dimethylformamide (DMF, 500 mL) in a 2 L flask fitted with a mechanical stirrer then potassium carbonate (72 g, 521.7 mmol) was added in as a single portion. The reaction was heated to 80° C. then benzyl chloride (42 mL, 363.5 mmol) was added dropwise. After 24 h at 80° C. the reaction was cooled down to room temperature. Acetone (400 mL) was added and the product was allowed to precipitate overnight. The solid orange product was filtered, washed with acetone and dried in a vacuum oven at 50° C. The O-benzylfluorescein benzyl ester was obtained as an orange solid (36.4 g, 59%): mp 192-193° C. (Lit. 193-194° C.); 1H NMR (DMSO-d6): 4.97 (dd, 2H, J=12.2 Hz, J=15.3 Hz), 5.28 (s, 2H), 6.13 (d, 1H, J=1.9 Hz), 6.36 (dd, 1H, J=9.9 Hz), 6.77 (d, 1H, J=9.9 Hz), 6.82 6.77 (d, 1H, J=9.0 Hz), 6.90-6.98 (m, 3H), 7.14-7.27 (m, 4H), 7.33-7.52 (m, 6H), 7.78 (dt, 1H, J=1.65 Hz, J=7.4 Hz), 8.23 (dd, 1H, J=1.35 Hz, J=7.7 Hz); 13C NMR (DMSO-d6): 67.4, 70.7, 101.9, 105.2, 114.7, 115.0, 117.3, 128.3, 128.5, 128.7, 128.8, 128.9, 129.4, 130.0, 130.2, 130.6, 130.8, 131.2, 131.4, 133.8, 134.1, 135.3, 136.6, 150.1, 153.9, 158.7, 163.3, 165.5, 184.4; IR (nujol) cm−1 1728, 1643, 1595, 1517, 1462, 1377, 1261, 1211, 1081, 855. C34H24O5: Calc.(C, 79.67; H, 4.72) Found (C, 79.74; H, 4.79).
