1: CH3CBr2CO2Et With tert.-butyl lithium in tetrahydrofuran T=-78 - 0°C; 3.5 h; 2: 3-(tert-butyldimethylsilyloxy)2-butanone in tetrahydrofuran T=20°C; 0.5 h; 3: With hydrogenchloride in ethanol Further stages.;