The first synthesis of the title compound 4, a novel analog of 1α-hydroxyvitamin D (α-calcidiol) that might be therapeutically useful, is described. A key feature in the synthesis is the radical deoxygenation of the diol 21, which was prepared according to the previously reported procedure starting from 17. The resulting deoxygenated product 22 with the desired side-chain moiety was finally led to 4 in a conventional manner. Some aspects of the unusual reactivity of 25-OH on radical deoxygenation are also discussed.