7,8-(2,2-Dimethyl-2H-pyran)-5,4-dihydroxyflavonol (Sophorol, 12):(CH3)2SO4 (10.53 mmol, 1.0 mL) was added dropwise to a stirred solution of 11 (500 mg, 1.02 mmol) in NaOH (5% aqueous solution; 15 mL). The mixture was stirred at room temperature and maintained at pH 9-10 for 5 hours. Thereafter, the reaction mixture was adjusted to pH 6 using HCl (2% aqueous solution) and then extracted with the mixture. Water anhydrous Na2SO4 was dried free and the solvent was evaporated. The solid residue was recrystallized EtOAc/petroleum ether from it to give locust flavanol (181 mg, 96%) as yellow needles with a melting point melting point 272-274C.
