1: Et3N / tetrahydrofuran / 0.42 h / -10 °C 2: aq. MH3 / tetrahydrofuran / 0.75 h / -10 °C 3: 85 percent / Lawesson's reagent / CH2Cl2 / 16 h / Ambient temperature 4: KHCO3 / 1,2-dimethoxy-ethane / 16 h / -15 °C 5: TFAA, 2,6-lutidine / 1,2-dimethoxy-ethane / 0.5 h / -10 °C 6: 87 percent / aq. LiOH / methanol / 3 h / Ambient temperature View Scheme

1: aq. MH3 / tetrahydrofuran / 0.75 h / -10 °C 2: 85 percent / Lawesson's reagent / CH2Cl2 / 16 h / Ambient temperature 3: KHCO3 / 1,2-dimethoxy-ethane / 16 h / -15 °C 4: TFAA, 2,6-lutidine / 1,2-dimethoxy-ethane / 0.5 h / -10 °C 5: 87 percent / aq. LiOH / methanol / 3 h / Ambient temperature View Scheme

1: 90 percent / 5.5 N hydrochloric acid / 16 h / Heating 2: 1.) sodium hydroxide / 1.) dioxane, 3 h, 0 deg C, 2.) 1 h, RT View Scheme

sodium hydroxide 1.) dioxane, 3 h, 0 deg C, 2.) 1 h, RT; Yield given. Multistep reaction;

1.1: benzotriazol-1-ol; 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride; N-ethyl-N,N-diisopropylamine / tetrahydrofuran; dichloromethane / 0.17 h 2.1: triethylamine; trifluoroacetic anhydride / dichloromethane / 0 °C 3.1: sodium hydrogencarbonate / methanol / 2 h / 70 °C / pH 6 / aq. phosphate buffer 4.1: benzotriazol-1-yloxyl-tris-(pyrrolidino)-phosphonium hexafluorophosphate; N-ethyl-N,N-diisopropylamine / dichloromethane / 0.17 h / 0 °C 4.2: 0 - 20 °C 5.1: trifluoroacetic acid / dichloromethane / 0 - 20 °C 6.1: benzotriazol-1-ol; N-ethyl-N,N-diisopropylamine; HATU / dichloromethane; acetonitrile 7.1: triethylsilane; trifluoroacetic anhydride / 2 h / 0 - 20 °C 8.1: triethylamine / dichloromethane / 3 h / 0 - 20 °C View Scheme

trifluoroacetic acid in dichloromethane 0.5 h;