A review with 47 refs. covers a convergent strategy for prepg. vitamin D group compds., based on one key intermediate (C-22 vitamin a1c.) and affording not only the major vitamin D 3 metabolite but also analogs modified at the aliphatic side chain. The analogs are active components in drugs or new compds. endowed with a therapeutic activity. The key intermediate is now prepd. from ergocalciferol. Analogs are prepd. by adding a side-chain fragment (prepd. sep.) to the vitamin synthon. The strategy is illustrated by syntheses of vitamin D-2 and D-3 analogs which may have a therapeutic value.