Calciferol and its relatives. Part 28. A stereoselective synthesis of 1 α-hydroxyprecalciferol3 from 8-hydroxymethyl-des-AB-cholest-8-ene
Abstract
8-p-Tolylsulphonylmethyl-des-AB-cholest-8-ene (1) and methyl (3S,5R)-3,5-bis-t-butyldimethylsilyloxy-2-methylcyclohex-1-enecarboxylate (2) were combined to give a 6-oxo-7-sulphone from which 1 α,3β-diacetoxy 9,10-seco-cholesta-5(10),8-diene-6-yne (4) was obtained. Semihydrogenation and deacetylation gave 1α-hydroxyprecalciferol3(6), which was converted by thermal isomerisation into 1α-hydroxyvitamin D3(7).