1: tert-butyl 4-oxo-piperidine-1-carboxylate With lithium hexamethyldisilazane in tetrahydrofuran; diethyl ether T=-78°C; 0.5 h; 2: oxalic acid diethyl ester in tetrahydrofuran; diethyl ether T=20°C; 3: With hydrogenchloride in tetrahydrofuran; diethyl ether; water

acetic acid; hydrazine 16 h;