p-Toluenesulfonic acid (78 mg, 0.41 mmol), 3,4-dihydro-2H-pyrane (20.1 ml, 0.098 mol) were added to a solution of methyl 3α,7α-dihydroxy-5β-cholan-24-oate (1) (2.0 g, 4.9 mmol) in dioxane (6 mL). The reaction mixture was stirred at room temperature for 15 min. H2O (50 mL) was then added and the mixture was partially concentrated under vacuum and extracted with EtOAc (3×50 mL). The combined organic fractions were washed with brine (1×50 mL), dried (Na2SO4) and evaporated under vacuum. The residue was purified by chromatography on silica gel column. Elution with light petroleum/ethyl acetate 80/20 afforded 2.5 g of the pure compound 2 (90% yield).
