Aldehyde (I), derived from vitamin D2, was submitted to a Reformatsky reaction with ethyl bromodifluoroacetate and activated Zn to produce a mixture of diastereomeric b-hydroxyesters (II). After chromatographic separation, the required (23S)-isomer was condensed with MeMgBr to give tertiary alcohol (III). Finally, desilylation of (III) with tetra n-butylammonium fluoride in THF provided the title compound.