1: BH3 / tetrahydrofuran / 72 h / Heating 2: 88 percent / DMAP, NEt3 / CH2Cl2 / 0 °C 3: POCl3 / benzene / Heating 4: NaBH4 / methanol / 4 h / -78 °C 5: 82 percent / H2 / Pd/C / ethanol; aq. HCl View Scheme

1.1: 4-(N,N-dimethlyamino)pyridine; boron trifluoride diethyl etherate; B2H6*Me2S / 3 h / 70 °C 2.1: dicyclohexyl-carbodiimide; 4-(N,N-dimethlyamino)pyridine / dichloromethane / 2 h / 20 °C 3.1: trichlorophosphate / benzene / 7 h / |Reflux 3.2: 3 h / 20 °C / |Inert atmosphere 4.1: boron tribromide / dichloromethane / 2 h / -78 - 20 °C View Scheme

Stage #1: With  boron trifluoride diethyl etherate; complex boron hydride with tetrahydrofurane in  tetrahydrofuran 2 h;  Inert atmosphereReflux; Stage #2: With  hydrogenchloride in  tetrahydrofuran; water T=0°C; 12 h;   

Multi-step reaction with 2 steps 1: BH3 / tetrahydrofuran / 72 h / Heating2: 88 percent / DMAP, NEt3 / CH2Cl2 / 0 °C  

Multi-step reaction with 3 steps 1: BH3 / tetrahydrofuran / 72 h / Heating2: 88 percent / DMAP, NEt3 / CH2Cl2 / 0 °C3: POCl3 / benzene / Heating  

Multi-step reaction with 4 steps 1: BH3 / tetrahydrofuran / 72 h / Heating2: 88 percent / DMAP, NEt3 / CH2Cl2 / 0 °C3: POCl3 / benzene / Heating4: NaBH4 / methanol / 4 h / -78 °C