(1S,3R)-Cholesta-5,7-diene-1,3,25-triol, a photochemical reaction precursor for the preparation of 1α,25-dihydroxyvitamin D₃ , was synthesized by utilizing the intact skeleton of diosgenin in 16 steps in 7.6% overall yield. The reductive E/F ring opening of 3-benzyloxy-diosgenin produced 3,16,26-cholesteratriol benzyl ether 5. The C-26 hydroxy group was shifted to C-25 through the elimination and hydroxylation after the selective removal of C-16 hydroxyl group in 5. The A/B structural unit of the target molecule was constructed by the functional transformation of the A/B ring of diosgenin. (1S,3R)-Cholesta-5,7-diene-1,3,25-triol can be converted into 1α,25-dihydroxyvitamin D₃ according to the known photochemical reaction.

Key words: 1α,25-dihydroxyvitamin D₃, diosgenin, (1S,3R)-cholesta-5,7-diene-1,3,25-triol, resource chemistry