Synthesis of the Enantiomer of 1alfa,25-Dihydroxy Vitamin D3(calcitrol) and a Diastereomer of 1alfa,25-Dihydroxy Vitamin D3, Differing from Natural Product in Configuratoion at All but One Asymmetric Carbon Atoms

Convergent synthesis of ent-1alfa,25-dihydroxyvitamin D3 (ent-calcitriol, 2) and (1S,3S, 13S,14S,17S,20S) - 1alfa,25-dihydroxyvitamin D3 (5) using the ring A building blocks, 6 and 7, respectively, and rings CD building block8, is described. Building block 6 was obtained starting from vitamin D3 via dihydroxylation of the C7-C8 double bond, Mitsunobu inversion at C3, diastereoselective hydroxylation at C1 and cleavage of the C7-C8 bond. Building block 7 was prepared from known synthetic intermediate, 16a(1R,3S) via benzylation of the primary hydroxy group, mono-deprotection of bis-silyl ether 16b and Mitsunobu inversion of the configuration at C3 in 19. Synthetic building blocks were combined using Julia-Kocienski olefination reaction. Key words:Vitamins D, convergent synthesis, Mitsunobu reaction, olefination reaction