1: 88 percent / LDA; HMPA / tetrahydrofuran / 4 h / -78 °C 2: 75 percent / trifluoroacetic acid / CH2Cl2 / 3 h / 20 °C 3: aq. NaOH / 72 h / 20 °C 4: 16 mg / triethylamine; bis(2-oxo-3-oxazolidinyl)phosphonic chloride / CH2Cl2 / 3 h / 20 °C View Scheme

1: N,N,N',N',N'',N''-hexamethylphosphoric triamide; lithium diisopropyl amide / tetrahydrofuran; hexane / 4 h / -78 °C 2: trifluoroacetic acid / dichloromethane / 4 - 20 °C 3: water; sodium hydroxide / 64 h / 4 °C View Scheme