Reaction Steps
A solution of 3,4-bis-(1,1-dimethyl-allyloxy)-xanthen-9-one (229 mg, 0.587 mmol) in toluene (10 mL) was refluxed under argon for 2 h. The solvent was evaporated and the residue was purified by column chromatography (SiO2, EtOAc:hexanes/10-30%) to give the title compound as white solids (145 mg, 63%): 1H NMR (CDCl3, 300 MHz) δ 7.95 (dd, J=1.5, 7.8 Hz, 1H), 7.53 (ddd, J=1.5, 7.2, 8.1 Hz, 1H), 7.44 (dd, J=0.6, 7.2 Hz, 1H), 7.07 (m, 2H), 4.42 (m, 1H), 3.50 (dd, J=4.5, 6.9 Hz, 1H), 2.63 (m, 2H), 2.46 (d, J=9.3 Hz, 1H), 2.35 (dd, J=4.2, 12.6 Hz, 1H), 1.73 (s, 3H), 1.31 (m, 1H), 1.31 (s, 6H), 0.92 (s, 3H); 13C NMR (CDCl3, 75 MHz) δ 202.8, 176.3, 159.5, 136.1, 134.8, 134.7, 133.6, 126.8, 121.8, 119.0, 118.9, 118.0, 90.3, 84.6, 83.5, 48.8, 46.8, 30.4, 29.2, 25.4, 25.2, 16.8.
