1: ethyl 2-oxo-cyclohexanecarboxylate With sodium hydride in tetrahydrofuran T=0°C; 0.166667 h; 2: With n-butyllithium in tetrahydrofuran; hexane T=0°C; 0.416667 h; 3: 4-bromo-but-1-ene in tetrahydrofuran; hexane T=0 - 20°C; 22 h; Further stages.;