Synthesis of 24ξ,25-dihydroxyprovitamin D3

Abstract

The known C-22 aldehyde obtained by degradation of ergosterol acetate (in which the ring B diene system has been protected by Diels–Alder addition of 4-phenyl-1,2,4-triazoline-3,5-dione) undergoes aldol condensation with 3-methyl-3-tetrahydropyranyloxybutan-2-one. The resulting enone gives 24ξ,25-dihydroxyprovitamin D₃(the provitamin of the metabolite 24,25-dihydroxycholecalciferol) upon successive reductions with sodium borohydride in pyridine and lithium aluminium hydride.