trifluoroacetic anhydride in dichloromethane T=0 - 20°C; 3 h;

1: 77 percent / methanol / 20 h / Heating 2: 98 percent / H2 / Pd(OH)2/C / methanol / 12 h / 20 °C 3: 93 percent / Et3N; 4-(dimethylamino)pyridine / CH2Cl2 / 1.75 h / 0 - 20 °C 4: 91 percent / aq. LiOH / tetrahydrofuran / 15 h / 20 °C 5: 98 percent / trifluoroacetic anhydride / CH2Cl2 / 3 h / 0 - 20 °C View Scheme

1: 98 percent / H2 / Pd(OH)2/C / methanol / 12 h / 20 °C 2: 93 percent / Et3N; 4-(dimethylamino)pyridine / CH2Cl2 / 1.75 h / 0 - 20 °C 3: 91 percent / aq. LiOH / tetrahydrofuran / 15 h / 20 °C 4: 98 percent / trifluoroacetic anhydride / CH2Cl2 / 3 h / 0 - 20 °C View Scheme

1: 93 percent / Et3N; 4-(dimethylamino)pyridine / CH2Cl2 / 1.75 h / 0 - 20 °C 2: 91 percent / aq. LiOH / tetrahydrofuran / 15 h / 20 °C 3: 98 percent / trifluoroacetic anhydride / CH2Cl2 / 3 h / 0 - 20 °C View Scheme

1: 91 percent / aq. LiOH / tetrahydrofuran / 15 h / 20 °C 2: 98 percent / trifluoroacetic anhydride / CH2Cl2 / 3 h / 0 - 20 °C View Scheme