1: chlorosulfonic acid / 30 °C 2: Tris-HCl buffer; aq. NaOH / tetrahydrofuran / 4 h / 20 °C / pH 8 - 9 3: N-(3-(dimethylamino)propyl)-N-ethylcarbodiimide*HCl / methanol / 20 °C 4: polyphosphoric acid trimethylsilyl ester / 120 - 170 °C 5: aq. NaOH / 0.5 h / 70 °C View Scheme

chlorosulfonic acid T=30°C;

1: With chlorosulfonic acid T=100°C; 3 h; 2: With sodium azide in water; acetone T=40°C; 2.5 h;

thionyl chloride; N,N-dimethyl-formamide 4 h; Inert atmosphereReflux;