Stereoselective synthesis of 25S,26-dihydroxyvitamin D3

•A convergent synthesis of 25S,26-dihydroxyvitamin D3 was achieved for biological testing.•An efficient and versatile synthetic approach to the all isomers of 25,26-dihydroxyvitamin D3 was established by osmium catalyzed asymmetric dihydroxylation.•The construction/formation of the triene moiety/system was done by the Wittig-Horner approach. A convergent approach to 25S,26-dihydroxyvitamin D3 (1) has been developed in our laboratories. The A-ring and the CD-fragment are constructed from ergocalciferol and Inhoffen-Lythgoe diol, respectively. The triene system is assembled by a Wittig-Horner coupling. With this convergent synthesis, a novel hydroxylated vitamin D metabolite in our laboratory is available for biological testing.