in diethyl ether T=0°C;

1: 82 percent / n-BuLi / hexamethylphosphoric acid triamide; hexane / rt, 15 min, 50 deg C, 30 min, 0 deg C to rt, 1 h, 50 deg C, 2 h 2: 77 percent / CrO3, H2SO4 / acetone / -5 deg C, 30 min, rt, 3 h 3: 100 percent / diethyl ether / 0 °C View Scheme