1: triphenylphosphine, diizopropylazodicarboxylate / tetrahydrofuran / 2.5 h / 25 °C 2: sodium methoxide / methanol / 40 h / -5 °C 3: imidazole / dimethylformamide / Ambient temperature 4: 1.) lithium diisopropylamide, HMPA / 1.) THF, hexane, -78 deg C, 40 min, 2.) THF, hexane, -78 deg C, 1.5 h 5: 1.) lithium diisopropylamide, HMPA, 2.) acetic acid / 1.) THF, hexane, -78 deg C, 0.5 h, 2.) THF, hexane, -78 deg C, 5 min 6: 83 percent / NaOH / methanol; H2O / 1.) RT, 0.5 h, 2.) 50 deg C, 1 h View Scheme