An efficient route to 1α,25-dihydroxyvitamin D3 functionalized at C-11

An efficient route to vitamin D3 analogues functionalized at C-11 is described. Key features of this synthesis are: (i) the development of a novel and efficient route for the introduction of the 25-hydroxylated side chain, present in the most important metabolites of vitamin D3, and (ii) the stereoselective functionalization of the C-ring of 1α,25-(OH)2-D3 at C-11.