1: 1.) t-butyl-lithium / 1.) THF, -70 deg, 1 h 2: 10percent aq. H2SO4 / diethyl ether / 1 h / 0 °C 3: 82 percent / 40percent aq. HF / acetonitrile / 2 h / 20 °C View Scheme

1: t-BuLi / tetrahydrofuran; pentane / 0.75 h / -50 °C 2: HMPA / -20 °C 3: 85 percent / n-Bu4NF / tetrahydrofuran / 12 h / 20 °C 4: 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;