Synthesis of 25ξ,26-dihydroxyvitamin D2

Abstract

Both acetylenic alcohols available from the attack of propynylmagnesium bromide on a steroidal C-22 aldehyde were utilised to generate a common γδ-unsaturated ester via a Claisen rearrangement. This ester was then converted into the title compound in a reaction sequence in which C-25 hydroxylation was achieved via oxygenation of the enolate anion of the C-26 ester function.