Calciferol and its relatives. Part XVI. Total synthesis of precalciferol32

Abstract

The total synthesis of precalciferol₃ has been effected without the use of photochemical methods. 9α-Chloro-des-AB-cholestan-8-one {5α-chloro-1β-[(1R)-1,5-dimethylhexyl]-7aβ-methyl-trans-perhydroindan-4-one}(1; X =α-Cl) and (1S)-3-ethynyl-4-methylcyclohex-3-en-1-ol (2; R = H) were combined to give the chlorohydrin (3; X =α-Cl), which was transformed, first into the dienyne (4) and then, by semihydrogenation of the acetylene link, into precalciferol₃(5). Model experiments, bearing on this and related routes to the pre-vitamin, are described.