1.1: oxalyl dichloride / N,N-dimethyl-formamide / dichloromethane / 0 - 23 °C / Inert atmosphere 2.1: sodium azide / water; acetone / 1 h / 0 °C 3.1: 36 h / 90 °C 4.1: hydrazine hydrate / ethanol / 14 h / 50 °C / Inert atmosphere 4.3: pH 11 View Scheme