1: With n-butyllithium; diisopropylamine in tetrahydrofuran; hexanes T=-78°C; 0.5 h; 2: acetonitrile in tetrahydrofuran; hexanes 0.5 h; 3: 4-formyl-piperidine-1-carboxylic acid tert-butyl ester in tetrahydrofuran; hexanes 2 h;