title: Norrish-Prins reaction as a key step in the synthesis of 14β-hydroxy-5α (or 5β or Δ(5,6))-pregnane derivatives.
abstract: Numerous bioactive glycosteroids are characterized by aglycones bearing a 14β-hydroxy pregnane skeleton like boucerin and isoramanone. In general, the syntheses of the latter are achieved by acidic hydrolysis of the corresponding glycosteroids. These aglycones were also obtained by a combined Norrish type I-Prins reaction starting from the corresponding 12-keto-pregnane derivatives. However, for the Norrish-Prins reaction, no reports describe the influence of the A/B ring junction (cis or trans or Δ(5,6) double bond) or the influence of the substitution pattern at position 20. Herein, we describe the use of Norrish type I-Prins reactions to synthesize isoramanone and boucerin derivatives and their A/B cis and trans analogs. The influence of the parameters mentioned above is also presented. These studies showed that the A/B ring junction has little influence on the Norrish type I-Prins reaction but that the substitution pattern at position 20 is important. The presence of a dioxolane group induced not only the formation of the desired 14β-hydroxy pregnane derivatives in the highest yields but also the formation of new spiro derivatives.
authors.affiliation: Université de Strasbourg, Institut de Chimie, Université, UMR 7177, Laboratoire de Chimie Organique Synthétique, 1 rue Blaise Pascal, BP 296/R8, 67008 Strasbourg-Cedex, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Geoffroy
authors.forename: Blandine
authors.initials: B
authors.lastname: Ressault
authors.forename: Eric
authors.initials: E
authors.lastname: Marchioni
authors.forename: Michel
authors.initials: M
authors.lastname: Miesch
mesh_terms: D015394:Molecular Structure; D010777:Photochemistry; D011278:Pregnanes / Q000138:chemical synthesis* / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D011278:Pregnanes