Abstract: The present invention is a process for the preparation of 17?-hydroxy-7?-methyl-19-nor-17?-pregn-5(10)-en-20-yn-3-one (17?-ethynyl-17?-hydroxy-7?-methyl-5(10)-estren-3-one, tibolone) of formula 1, which comprises hydrolysis of 17?-ethynyl-17?-hydroxy-7?-methyl-5(10)-estrene 3,3-cyclic ketals of formula 2, where groups R1, R2, R3 and R4 are hydrogen atoms or alkyl groups, or R1 and R3, taken together with the carbon atoms within the dioxolane ring to which they are attached, form an alicyclic ring fused to the dioxolane ring, with R2 and R4 being hydrogen atoms, or R1 and R3 together with the carbon atoms to which they are attached form an aromatic ring fused to the dioxolane ring, where R2 and R4, taken together, form a chemical bond within said aromatic ring.

Abstract: Vitamin D.sub.3 analogues of the formula (I): ##STR1## wherein R.sub.1 is hydrogen or hydroxy, R.sub.2 is hydrogen, (C.sub.1 -C.sub.3) alkyl, phenyl, or trifluoromethyl, R.sub.3 is branched or unbranched (C.sub.1 -C.sub.4) alkyl, cyclopropyl or CF.sub.3, A and B are individually hydrogen or methyl, or A and B together form methylene, X is CH.sub.2 or O, and n is 2 or 3. These compounds are useful for treating various skin and bone disorders and cancers. These compounds are also useful in cosmetic applications and for diagnostic purposes. Compounds of formula (I) are prepared by reacting a C--25 ester compound with an organometallic compound or by coupling a CD ring ester moiety with a Wittig reagent or an enyne compound to form the desired diene or triene system.