1: 90 percent / NaOH / tetrahydrofuran; H2O / 35 h 2: tetrahydrofuran; hexamethylphosphoric acid triamide / 1) 5-8 deg C, 2) to 25 deg C 3: citric acid / tetrahydrofuran; H2O; petroleum ether / 6 h 4: CHCl3 / 0.33 h / 40 °C View Scheme