1: With n-butyllithium; N,N,N',N'',N''-pentamethyldiethylenetriamine in tetrahydrofuran; hexane T=-78°C; 3 h; 2: With boric acid trimethyl ester in tetrahydrofuran; hexane T=20°C; 2 h; 3: With dihydrogen peroxide; acetic acid in tetrahydrofuran; hexane T=0°C; Further stages.;