Calciferol and its relatives. Part 27. A synthesis of 1 α-hydroxyvitamin D3 by way of 1 α-hydroxytachysterol3

Abstract

A new synthesis of 1 α-hydroxyvitamin D₃ is described. The bis-t-butyldimethylsilyl ether (17) of (3S,5R)-3,5-dihydroxy-2-methylcyclohex-1-enecarbaldehyde and 8-p-tolylsulphonylmethyl-des-AB-cholest-8-ene (4) were combined to give mixed benzoyloxysulphones which, on reductive elimination with sodium amalgam, gave the corresponding bis-ether of 1 α-hydroxytachysterol₃. This was isomerised photochemically to the bis-ether of 1 α-hydroxyprecalciferol₃, and then thermally to give the bis-ether of 1 α-hydroxyvitamin D₃. Removal of protecting groups gave 1 α-hydroxyvitamin D₃(21) in 62% yield from the sulphone (4), or 12,8% overall from cholesterol.