1: 4-(N,N-dimethlyamino)pyridine; triethylamine / tetrahydrofuran / 20 °C / Reflux 2: tetrabutyl ammonium fluoride; acetic acid / tetrahydrofuran / 20 °C 3: N,N,N',N',N'',N''-hexamethylphosphoric triamide; lithium diisopropyl amide / tetrahydrofuran; hexane / 4 h / -78 °C 4: trifluoroacetic acid / dichloromethane / 4 - 20 °C 5: water; sodium hydroxide / 64 h / 4 °C 6: bis-(2-oxo-3-oxazolidinyl)phosphoryl chloride; triethylamine / dichloromethane / 2 h View Scheme

1: 4-(N,N-dimethlyamino)pyridine; triethylamine / tetrahydrofuran / 20 °C / Reflux 2: tetrabutyl ammonium fluoride; acetic acid / tetrahydrofuran / 20 °C 3: N,N,N',N',N'',N''-hexamethylphosphoric triamide; lithium diisopropyl amide / tetrahydrofuran; hexane / 4 h / -78 °C 4: trifluoroacetic acid / dichloromethane / 4 - 20 °C 5: water; sodium hydroxide / 64 h / 4 °C View Scheme