sulfuric acid 240 h; Heating;

1: (2S)-(-)-trans-4-hydroxy-proline With acetic anhydride; acetic acid 2: ethanol With hydrogenchloride

thionyl chloride T=20°C;

1.1: acetic anhydride; acetic acid / 5.5 h / 50 °C / Reflux 1.2: 3 h / Reflux 2.1: thionyl chloride / 20 °C View Scheme

1: i-Pr2NEt / CH2Cl2 / Ambient temperature 2: 98 percent / oxalyl chloride, DMSO / CH2Cl2 / 2 h / -78 °C 3: ethanol; H2O / 48 h / 55 °C 4: 1.) aq. NaOH, 2.) SOCl2 / 1.) reflux, overnight, 2.) reflux, 3 d 5: 100 percent / CH2Cl2 / Ambient temperature 6: 85 percent / H2 / 5percent Pd/C / ethanol / 4 h / 3102.9 Torr / Ambient temperature 7: 1.) HCl (gas), 2.) 1 N aq. NaOH / 1.) Et2O, RT, 1 h, 2.) THF, RT, overnight View Scheme

1: sodium hydrogencarbonate / 1,4-dioxane; water / 0 - 20 °C 2: lithium borohydride / tetrahydrofuran / 0 - 20 °C / Inert atmosphere View Scheme