1: 2-[1-(tert-butoxycarbonyl)-4-piperidyl]acetic acid With 1,1'-carbonyldiimidazole in tetrahydrofuran T=20°C; 5 h; 2: malonic acid ethyl ester monopotassium salt With magnesium chloride in tetrahydrofuran T=20°C; 23 h; Heating / reflux; 3: With hydrogenchloride in tetrahydrofuran; water T=0°C; pH=7;