Stereoselective synthesis of vitamin D3 analogues with cyclic side chains

The synthesis of a new class of vitamin D analogues having a cyclic side chain is described. Readily available starting material, a short sequence with high yielding steps are key features of the synthesis. Alcohols 12c and 12d were readily separable by flash chromatography and the stereochemistry at C22 was established unambiguously by X-ray diffraction analysis of 12c.