Ligand Tuning in Asymmetric Hydrovinylation of 1,3-Dienes: A Stereoselective Route to Either Steroid-C20 (S) or -C20 (R) Derivatives

In this paper we report the results of these studies which demonstrate that in these steroids it is possible to install, with complete stereoselectivity, either C20 or C20 configuration by proper choice of ligands and reaction conditions

Biswajit Saha; Craig R. Smith; T. V. RajanBabu

2008

Scholarcy highlights

  • A chiral side-chain carrying a methyl group is a very common structural motif in many terpenoids and this side-chain is often attached at a stereogenic center of a ring
  • Examples can be found in simple sesquiterpenes such as juvenile hormone juvabione, or in more complex structures such as pseudopterosins, elisabethin A,3 ophiobolin C,4 steroid hormone calcitriol and its analogs, antitumor agents cephalostatins and various cytotoxic steroidal glycosides
  • Several creative solutions to the problem of installation of these stereogenic centers have been developed over the years, even though no broadly applicable method that uses readily available precursors has emerged
  • Consider for example, precursors for calcitriol analogs with exocyclic C20-configuration, which have been shown to have significant biological activity. These molecules are currently prepared by circuitous routes that involve the equilibration of the aldehyde 2, obtained from vitamin D2 and subsequent reactions of the minor isomer isolated from the mixture
  • Here we disclose a new highly stereoselective, ligand-dependent protocol for the installation of exocyclic stereocenters in a steroid D-ring via asymmetric hydrovinylation
  • A slight modification of the reaction allows the stereoselective preparation of C16-vinyl derivatives

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