To a mixture of magnesium (24 g, 1.00 mole) in dry ether (500 ml) was added dropwise 2-bromopropane (60 ml, 639 mmole) while stirring. After the addition was completed, the reaction mixture was stirred for thirty minutes. The ethereal solution was transferred to another flask. Then to the resulting isopropyl-magnesium bromide solution was added portionwise cadmium bromide (75 g, 276 mmole) at room temperature. The resulting dark solution was refluxed gently for one hour, followed by the addition of dry benzene (200 ml), then most of the ether was removed. To this mixture, 3β-acetoxy-5-cholenic acid chloride 331 (50 g, 115 mmole) in dry benzene (300 ml) was added dropwise. The reaction mixture was stirred at room temperature for one hour and then poured slowly into a crushed ice and 10% hydrochloric acid mixture. The organic layer was separated. The aqueous layer was extracted with ether (3×300 ml). The combined ethereal solution was washed with 10% HCl, washed with water, dried (MgSO4), filtered, and concentrated in vacuo to give crude product, 3β-acetoxy-24-oxo-5-cholestene 332 (35.6 g, 70% yield), which was used for the next reaction without further purification. 1H NMR (400 MHz, CDCl3) δ: 0.69 (3H, s, 18-CH3), 0.95 (3H, d, 21-CH3), 1.04 (3H, s, 19-CH3), 1.25 (6H, 2d, 26-CH3, 27-CH3), 2.04 (3H, s, --OCOCH3), 4.61 (1H, m, 3α-H), 5.38 (1H, m, 6-H).
