1: trifluoroacetic acid / dichloromethane / 19 h / 0 - 20 °C 2: triethylamine / dichloromethane / 0.17 h / 0 °C 3: sodium azide / water; N,N-dimethyl-formamide / 18 h / 90 °C 4: hydrogen / ethanol / 18 h / 20 °C 5: phosphoric acid / ethanol / 0.5 h / 55 °C View Scheme