Synthesis of New Aromatic (C17−C20)-Locked Side-Chain Analogues of Calcitriol (1α,25-Dihydroxyvitamin D3),1

The synthesis of four new analogues of calcitriol (1α,25-(OH)2-D3)possessing aromatic and conjugated double bond units at the side chain are described. The triene system is introduced using the Lythgoe−Hoffmann La Roche convergent Wittig−Horner approach. The key steps in the preparation of the requisite upper fragments are the introduction of the side chain with the E-conjugated aromatic system and its photochemical conversion to the Z counterpart.