1: C8H16N2O2 With n-butyllithium in tetrahydrofuran; hexane T=-78 - 20°C; 1 h; 2: oxalic acid diethyl ester in tetrahydrofuran; hexane T=-78 - 20°C; 16 h; 3: With toluene-4-sulfonic acid in toluene 8 h; Heating; Further stages.;