Norrish–Prins reaction as a key step in the synthesis of 14β-hydroxy-5α (or 5β or Δ5,6)-pregnane derivatives

Add time:09/26/2019    Source:sciencedirect.com

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 Δ5,6 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.

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