1: HMPA / -20 °C 2: 85 percent / n-Bu4NF / tetrahydrofuran / 12 h / 20 °C 3: 60 percent / pyridinium p-toluenesulphonate / methanol; CH2Cl2 / 12 h / 20 °C View Scheme

With  tert.-butyl lithium in  tetrahydrofuran; pentane T=-50°C; 0.75 h;