sodium hydroxide; dihydrogen peroxide in tetrahydrofuran -100°C, after 15 min warming to room temp. with stirring, keeping overnight, treating with H2O2-NaOH at 0°C, stirring for 1 h at room temp. and for 15 min at 50°C; Aq. phase is satd. with K2CO3, extd. with diethyl ether, combined organic phases are dried (K2CO3), concd., chromd. (silicagel, ethyl acetate-petroleum ether);