A convenient five-step route to 25-hydroxylated vitamin D3 compounds on (hydroxymethyl)polystyrene support is reported. A CD-side chain fragment was anchored to the solid phase through an ester group at C25 and coupled to an A ring building block to assemble the vitamin D triene system by the Wittig−Horner approach. Deprotection of the hydroxy group was carried out on the support, prior to functionalization