1: (1-phenyl-propylidene)-carbazic acid ethyl ester 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 10 h; Heating; Further stages.;

1: 67 percent / CH2Cl2; diethyl ether / 96 h / Heating 2: 41 percent / Heating View Scheme