1: With hydrogenchloride; water in isopropyl alcohol T=45°C; 6.5 h; 2: With sodium hydroxide in water

1.1: 2-methyl tetrahydrofuran / 22 °C 2.1: 2,2,6,6-tetramethyl-piperidine; n-butyllithium / hexane; tetrahydrofuran / -78 - -70 °C / Inert atmosphere 2.2: -20 °C / Inert atmosphere 3.1: hydrogenchloride; water / isopropyl alcohol / 6.5 h / 45 °C View Scheme

1.1: 2,2,6,6-tetramethyl-piperidine; n-butyllithium / hexane; tetrahydrofuran / -78 - -70 °C / Inert atmosphere 1.2: -20 °C / Inert atmosphere 2.1: hydrogenchloride; water / isopropyl alcohol / 6.5 h / 45 °C View Scheme

1.1: dichloromethane / 20 °C 1.2: 20.08 h / 14 - 30 °C 2.1: sodium hydroxide; water / dichloromethane / Cooling with ice 3.1: 2-methyl tetrahydrofuran / 22 °C 4.1: 2,2,6,6-tetramethyl-piperidine; n-butyllithium / hexane; tetrahydrofuran / -78 - -70 °C / Inert atmosphere 4.2: -20 °C / Inert atmosphere 5.1: hydrogenchloride; water / isopropyl alcohol / 6.5 h / 45 °C View Scheme

1.1: sodium hydroxide; water / dichloromethane / Cooling with ice 2.1: 2-methyl tetrahydrofuran / 22 °C 3.1: 2,2,6,6-tetramethyl-piperidine; n-butyllithium / hexane; tetrahydrofuran / -78 - -70 °C / Inert atmosphere 3.2: -20 °C / Inert atmosphere 4.1: hydrogenchloride; water / isopropyl alcohol / 6.5 h / 45 °C View Scheme

1.1: triethylamine / tetrahydrofuran / 20 h / 65 °C 2.1: lithium hexamethyldisilazane / tetrahydrofuran / 1 h / -78 °C 2.2: 0.5 h / -78 °C 2.3: 2 h / -78 - 0 °C 3.1: trifluoroacetic acid / dichloromethane / 16 h / 20 °C 4.1: benzotriazol-1-ol; 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride; N-ethyl-N,N-diisopropylamine / dichloromethane / 20 °C 5.1: N,N-diethylaniline / ethanol; hexane / Resolution of racemate View Scheme