1.1: zinc; ammonium chloride / water; tetrahydrofuran / 1 h / 50 °C / Inert atmosphere 1.2: 0.17 h / 23 °C / Inert atmosphere 2.1: triethylamine / toluene / 26 h / 110 °C / Inert atmosphere 3.1: trifluoroacetic acid / dichloromethane / 12 h / 23 °C / Inert atmosphere 4.1: oxalyl dichloride / N,N-dimethyl-formamide / dichloromethane / 0 - 23 °C / Inert atmosphere 5.1: sodium azide / water; acetone / 1 h / 0 °C 6.1: 36 h / 90 °C 7.1: hydrazine hydrate / ethanol / 14 h / 50 °C / Inert atmosphere 7.3: pH 11 View Scheme

Multi-step reaction with 3 steps 1: (R)-diphenylprolinol trimethylsilyl ether; chloroacetic acid / toluene2: caesium carbonate / 4 h / 0 - 20 °C3: -15 °C