sulfuric acid; nitric acid; urea in acetic anhydride T=-20 - 25°C;

sulfuric acid in sulfuric acid; nitric acid treatment of boronic acid deriv. with HNO3 and H2SO4 in presence of urea;

sulfuric acid; nitric acid; urea in acetic anhydride T=0 - 20°C;

sodium hydroxide; sulfuric acid; urea in water; acetic anhydride to aq. soln. nitric acid and sulfuric acid and few urea crystals at 0°C soln. 2-(trifluoronethyl)phenylboronic acid in acetic anhydride was slowly added and stirred for 4 h at 0°C; react. mixt. was poured onto ice and NaOH was added to pH 3-5, aq. phasewas extd. with Et2O, washed with brine, dried, and concd. in vacuo, rev erse-phase MPLC;