Chelerythrine (10, 0.20 mg) in dry dichloromethane (3 mL) was
stirred at 220uC under argon atmosphere for 30 min. Boron
tribromide (1 M, in dichloromethane, 5 mL) was added to the
mixture which was then stirred during 18 h. The reaction was
quenched by addition of methanol (10 mL). The solvent was
removed in vacuum and the residue was purified by reverse phase
liquid chromatography from methanol, to yield the 2,3-dihydroxy
chelerythrine derivative (14) in 33% yield, as a yellowish oil