1: 7-(tert-butoxycarbonyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[3,4-a]pyrazine With n-butyllithium in tetrahydrofuran; hexane T=-78°C; 0.25 h; 2: formic acid ethyl ester in tetrahydrofuran; hexane T=-78°C; 0.25 h;