Stereospecific synthesis of (22R)-22-hydroxycholesterol and (22R)-cholesta-5,24-diene-3β,22-diol

Abstract
A stereospecific method previously developed in the triterpene series for the synthesis of inotodiol (I) is shown to be equally valid in the steroid series. Addition of the appropriate Grignard reagent to (22ξ)-22,23-epoxy-6β-methoxy-3α,5α-cyclo-24-norcholane (VI) and (VII)[derived from the bromohydrins (Va–c)] furnished, after regeneration of the 5-en-3β-ol system, the title compounds in good yields, almost stereospecifically. It follows that electrophilic addition to the double bond occurs as previously defined for 24,25,26,27-tetranorlanosta-8,22-dien-3β-yl acetate, the (22S)-23-bromo-22-hydroxy- and (22R)-22-bromo-23-hydroxy-isomers being the major bromohydrins formed.

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