[CH3:1][CH:2]([CH2:4][CH2:5][CH2:6][C@H:7]([C@@H:9]1[C@:26]2([CH3:27])[C@H:12]([C:13]3[CH2:14][CH2:15][C:16]4[C@:21]([C:23]=3[CH2:24][CH2:25]2)([CH3:22])[CH2:20][CH2:19][C:18](=[O:28])[CH:17]=4)[CH2:11][CH2:10]1)[CH3:8])[CH3:3].CCC(C)[BH-](C(C)CC)C(C)CC.[Li+].Cl>O1CCCC1>[CH3:3][CH:2]([CH2:4][CH2:5][CH2:6][C@H:7]([C@@H:9]1[C@:26]2([CH3:27])[C@H:12]([C:13]3[CH2:14][CH2:15][C:16]4[C@:21]([C:23]=3[CH2:24][CH2:25]2)([CH3:22])[CH2:20][CH2:19][C@H:18]([OH:28])[CH:17]=4)[CH2:11][CH2:10]1)[CH3:8])[CH3:1].[CH3:3][CH:2]([CH2:4][CH2:5][CH2:6][C@H:7]([C@@H:9]1[C@:26]2([CH3:27])[C@H:12]([C:13]3[CH2:14][CH2:15][C:16]4[C@:21]([C:23]=3[CH2:24][CH2:25]2)([CH3:22])[CH2:20][CH2:19][C@@H:18]([OH:28])[CH:17]=4)[CH2:11][CH2:10]1)[CH3:8])[CH3:1]To a solution of 520 mg cholesta-4,8-dien-3-one in 45 ml tetrahydrofuran 1.70 ml of a L-Selectride solution (1 N, in tetrahydrofuran) are added dropwise at −75° C. The reaction mixture is warmed to room temperature within 4 hours, poured into hydrochloric acid (1 N) and extracted with ethyl acetate. The organic layer is separated, washed with brine, dried over anhydrous sodium sulphate and filtered. After evaporation of the solvent the residue is chromatographed with a mixture of hexane and ethyl acetate to give 286 mg cholesta-4,8-dien-3β-ol and 20 mg cholesta-4,8-dien-3α-ol as white solids.
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