oxalyl dichloride; dimethyl sulfoxide; triethylamine in dichloromethane T=-78 - 20°C; Swern oxidation;

1: With n-butyllithium in tetrahydrofuran; N,N,N',N',N'',N''-hexamethylphosphoric triamide; hexane T=0°C; 2 h; 2: With toluene-4-sulfonic acid in methanol T=20°C; 1 h;