[Preparation]
Cholan-24-ol (1.033 g, 3 mmol) was dissolved in dry benzene (10 mL) by gentle warming and dry dimethyl sulfoxide (10 mL) was added, followed successively by dry pyridine (0.24 mL, 3.0 mmol), distilled trifluoroacetic acid (0.12 mL, 1.5 mmol), and dicyclohexylcarbodiimide (1.85 g, 9 mmol). The flask was tightly stoppered and left at room temperature for 18 h. Benzene (30 mL) was then added, and the crystalline dicyclohexylurea formed was removed by filtration and washed with benzene. The combined filtrate and washings were washed with water (3×50 mL), dried over sodium sulfate, and concentrated under reduced pressure to give 2.12 g of a syrup, which partially crystallized. The crude product was dissolved in benzene/hexane, 1:1, and chromatographed on 125 g of silica gel with this solvent mixture to give cholan-24-al 1871 (0.87 g, 84%); mp 102–104 C°. |