Unusual Course of the Reaction of Allyl Phosphine Oxides with the Grundmann Ketone

<div><p></p><p>This article describes efficient preparation of isomeric allyl phosphine oxides possessing a protected cyclohexanediol fragment. Their base-catalyzed interconversions are examined and reactions with the Grundmann ketone provide an adduct containing the rearranged vinyl phosphine oxide moiety, instead of 19-norvitamin D₃ analogs, the expected products of the Horner–Wittig process.</p>