sodium tetrahydroborate in methanol T=-30 - -15°C; 1.5 h; Yield given;

1: NaBH4 / methanol / 1.5 h / -30 - -15 °C 2: 90 percent / imidazole / CH2Cl2 / 3 h 3: DIBAL-H / CH2Cl2; toluene / 2 h / -90 °C 4: molecular sieves (4 Angstroem), BF3*OEt2 / diethyl ether / 0.5 h 5: 1.) 1,1,1,3,3,3,-hexamethyldisilazane, ammonium sulfate, 2.) SnCl4, TMSOTf / 1.) reflux, 2 h, 2.) 1,2-dichloroethane, RT, 2 h 6: TBAF / tetrahydrofuran / 8 h 7: K2CO3 / methanol View Scheme

1: NaBH4 / methanol / 1.5 h / -30 - -15 °C 2: 90 percent / imidazole / CH2Cl2 / 3 h 3: DIBAL-H / CH2Cl2; toluene / 2 h / -90 °C 4: molecular sieves (4 Angstroem), BF3*OEt2 / diethyl ether / 0.5 h 5: 1.) 1,1,1,3,3,3-heksamethylenedisilazane, ammonium sulfate, 2.) SnCl4, TMSOTf / 1.) reflux, 2 h, 2.) 1,2-dichloroethane, RT, 2 h 6: TBAF / tetrahydrofuran / 8 h / Ambient temperature View Scheme

1: NaBH4 / methanol / 1.5 h / -30 - -15 °C 2: 90 percent / imidazole / CH2Cl2 / 3 h 3: DIBAL-H / CH2Cl2; toluene / 2 h / -90 °C 4: molecular sieves (4 Angstroem), BF3*OEt2 / diethyl ether / 0.5 h 5: 1.) 1,1,1,3,3,3,-hexamethyldisilazane, ammonium sulfate, 2.) SnCl4, TMSOTf / 1.) reflux, 2 h, 2.) 1,2-dichloroethane, RT, 2 h 6: TBAF / tetrahydrofuran / 8 h / Ambient temperature View Scheme