Synthesis of 1 alpha,3 beta-dihydroxy-2 beta-(3-hydroxypropoxy)-5,7-choladiene derivative and its application to the synthesis of 1 alpha,25-dihydroxy-2 beta-(3-hydroxypropoxy)vitamin D-3

Starting from 22-benzoyloxy-3 beta-(t-butyldimethylsilyloxy)-5 alpha,8 alpha-(4-phenyl-3,5-dioxo-1,2,4-triazolidine-1,2-diyl)-23,24-dinor-1,6-choladiene (5), the PTAD (4-phenyl-3H-1,2,4-triazole-3,5-(4H)-dione) adduct of 1 alpha,3 beta-dihydroxy-2 beta-(3-hydroxypropoxy)-23,24-dinor-5,7-choladiene derivative (3) was synthesized. The steroidal synthon (3) was converted to 1 alpha,25-dihydroxy-2 beta-(3-hydroxypropoxy)vitamin D-3 (2). Oxidation of 3 afforded the corresponding C-20 carbaldehyde (4).