1.1: hydrazine hydrate / tetrahydrofuran / 4 h / 0 - 15 °C 2.1: triethylamine / tetrahydrofuran / 1 h / 20 °C 3.1: acetic acid / tetrahydrofuran / 48 h / 20 °C 4.1: sodium hydroxide / tetrahydrofuran / 5 h / 20 °C 5.1: N-ethyl-N,N-diisopropylamine; HATU / tetrahydrofuran / 3 h / 20 °C 5.2: 48 h View Scheme