Water → (E)-Methyl 3alpha-acetoxy-5beta-chol-9(11),16,22-trien-24-oate

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Ethyl aluminum dichloride (104.5 mL, 192 mmol, 1.8 M in toluene) was added to a solution of methyl propiolate (13.58 mL, 153 mmol) in DCM (100 mL) at 0° C. under inert atmosphere. The resulting solution was stirred for 15 min and then compound 1.6a (22 g, 64.3 mmol) was added. After stirring for an additional 20 min at 0° C., the temperature was raised to 25° C. and held there for a further 18 h. At this point the reaction was determined to be complete by TLC, and the mixture was poured into cold (0° C.) water (200 mL). The phases were separated and the aqueous layer was extracted with DCM (150 mL). The organic layers were combined and washed sequentially with water (200 mL) and saturated brine solution (100 mL). It was then dried over anhydrous Na2SO4 (40 g) and filtered. The filtrate was concentrated under vacuum and the resulting solid was purified by slurring in methanol (280 mL) to provide compound 1.7a (17.5 g 68%) as a white solid.

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