3,4-dihydro-2H-pyran; toluene-4-sulfonic acid Yield given;

1: NaBH4 / methanol / 2 h / Ambient temperature 2: 5percent HCl / tetrahydrofuran / 25 °C View Scheme

1: 70 percent / NH4OAc, 15percent aq. TiCl3 / tetrahydrofuran / Ambient temperature 2: NaBH4 / methanol / 2 h / Ambient temperature 3: 5percent HCl / tetrahydrofuran / 25 °C View Scheme

1: LiAlH(Ot-Bu)3 / tetrahydrofuran / 1.) 18 h, RT 2.) 3 h, 60 deg C 2: 70 percent / NH4OAc, 15percent aq. TiCl3 / tetrahydrofuran / Ambient temperature 3: NaBH4 / methanol / 2 h / Ambient temperature 4: 5percent HCl / tetrahydrofuran / 25 °C View Scheme

1.1: CuCN / tetrahydrofuran; diethyl ether / 1 h / -30 °C 1.2: tetrahydrofuran; diethyl ether / 8 h / -12 °C 2.1: pyridinium p-toluenesulfonate / CHCl3 / 12 h / 20 °C 3.1: O3 / CH2Cl2 / -78 °C 3.2: Ph3P / CH2Cl2 / 12 h / 20 °C 4.1: benzene / 7 h / 65 °C 5.1: DIBAL-H / toluene; hexane / 1 h / -78 °C 6.1: PCC; NaOAc; molecular sieves 4 Angstroem / CH2Cl2 / 1 h / 0 °C 7.1: BuLi / tetrahydrofuran; hexane / 0.25 h / 0 °C 7.2: tetrahydrofuran; hexane / 3 h / -78 - 0 °C 8.1: tetrabutylammonium fluoride / tetrahydrofuran / 2 h / 20 °C 9.1: Dess-Martin reagent / CH2Cl2 / 1 h / 0 °C 10.1: Ni(cod)2; PPh3; i-Bu2-ALAC / toluene / 2 h / 0 °C 11.1: O3 / CH2Cl2 / -78 °C 11.2: PPh3 / CH2Cl2 / 15 h / 20 °C 12.1: PCC; 4 Angstroem molecular sieves; AcONa / CH2Cl2 / 2 h / 0 °C 13.1: Dowex 50wX8 / tetrahydrofuran; H2O / 3 h / 20 °C View Scheme

1.1: Ni(cod)2; PPh3; i-Bu2-ALAC / toluene / 2 h / 0 °C 2.1: O3 / CH2Cl2 / -78 °C 2.2: PPh3 / CH2Cl2 / 15 h / 20 °C 3.1: PCC; 4 Angstroem molecular sieves; AcONa / CH2Cl2 / 2 h / 0 °C 4.1: Dowex 50wX8 / tetrahydrofuran; H2O / 3 h / 20 °C View Scheme

1.1: pyridinium p-toluenesulfonate / CHCl3 / 12 h / 20 °C 2.1: O3 / CH2Cl2 / -78 °C 2.2: Ph3P / CH2Cl2 / 12 h / 20 °C 3.1: benzene / 7 h / 65 °C 4.1: DIBAL-H / toluene; hexane / 1 h / -78 °C 5.1: PCC; NaOAc; molecular sieves 4 Angstroem / CH2Cl2 / 1 h / 0 °C 6.1: BuLi / tetrahydrofuran; hexane / 0.25 h / 0 °C 6.2: tetrahydrofuran; hexane / 3 h / -78 - 0 °C 7.1: tetrabutylammonium fluoride / tetrahydrofuran / 2 h / 20 °C 8.1: Dess-Martin reagent / CH2Cl2 / 1 h / 0 °C 9.1: Ni(cod)2; PPh3; i-Bu2-ALAC / toluene / 2 h / 0 °C 10.1: O3 / CH2Cl2 / -78 °C 10.2: PPh3 / CH2Cl2 / 15 h / 20 °C 11.1: PCC; 4 Angstroem molecular sieves; AcONa / CH2Cl2 / 2 h / 0 °C 12.1: Dowex 50wX8 / tetrahydrofuran; H2O / 3 h / 20 °C View Scheme

1.1: O3 / CH2Cl2 / -78 °C 1.2: PPh3 / CH2Cl2 / 15 h / 20 °C 2.1: PCC; 4 Angstroem molecular sieves; AcONa / CH2Cl2 / 2 h / 0 °C 3.1: Dowex 50wX8 / tetrahydrofuran; H2O / 3 h / 20 °C View Scheme

1.1: Dess-Martin reagent / CH2Cl2 / 1 h / 0 °C 2.1: Ni(cod)2; PPh3; i-Bu2-ALAC / toluene / 2 h / 0 °C 3.1: O3 / CH2Cl2 / -78 °C 3.2: PPh3 / CH2Cl2 / 15 h / 20 °C 4.1: PCC; 4 Angstroem molecular sieves; AcONa / CH2Cl2 / 2 h / 0 °C 5.1: Dowex 50wX8 / tetrahydrofuran; H2O / 3 h / 20 °C View Scheme

1.1: O3 / CH2Cl2 / -78 °C 1.2: Ph3P / CH2Cl2 / 12 h / 20 °C 2.1: benzene / 7 h / 65 °C 3.1: DIBAL-H / toluene; hexane / 1 h / -78 °C 4.1: PCC; NaOAc; molecular sieves 4 Angstroem / CH2Cl2 / 1 h / 0 °C 5.1: BuLi / tetrahydrofuran; hexane / 0.25 h / 0 °C 5.2: tetrahydrofuran; hexane / 3 h / -78 - 0 °C 6.1: tetrabutylammonium fluoride / tetrahydrofuran / 2 h / 20 °C 7.1: Dess-Martin reagent / CH2Cl2 / 1 h / 0 °C 8.1: Ni(cod)2; PPh3; i-Bu2-ALAC / toluene / 2 h / 0 °C 9.1: O3 / CH2Cl2 / -78 °C 9.2: PPh3 / CH2Cl2 / 15 h / 20 °C 10.1: PCC; 4 Angstroem molecular sieves; AcONa / CH2Cl2 / 2 h / 0 °C 11.1: Dowex 50wX8 / tetrahydrofuran; H2O / 3 h / 20 °C View Scheme