1: With n-butyllithium in tetrahydrofuran; hexane T=-60°C; 8.75 h; Inert atmosphere; 2: With sulfur dioxide in tetrahydrofuran; hexane T=-65 - 20°C; 3: With NaOAc·3H2O; hydroxylamine-o-sulphonic acid in ethyl acetate T=0 - 20°C;