Benutzer:Kreuz Elf/Narasaka–Prasad-Reduktion
The Narasaka–Prasad reduction, sometimes simply called Narasaka reduction, is a diastereoselective reduction of β-hydroxy ketones to the corresponding syn-dialcohols. The reaction employs a boron chelating agent, such as BBu2OMe, and a reducing agent, commonly sodium borohydride. This protocol was first discovered by Narasaka in 1984.[1]
The reaction proceeds through the 6-membered transition state shown below. Chelation by the boron agent favors hydride delivery from the top face because it leads directly to the more stable chair-like conformation of the product (Fürst-Plattner Rule). The intermolecular hydride delivery from NaBH4 therefore proceeds via an axial attack from the opposite face with respect to the existing alcohol.[1]
This reaction can be contrasted with the similar Evans–Saksena reduction that employs a different boron reagent in order to achieve intramolecular hydride delivery from the same face of the alcohol, thus producing the anti-diol.
The Narasaka–Prasad reduction has been employed in many total syntheses in the literature,[2] such as discodermolide[3]
See also
[Bearbeiten | Quelltext bearbeiten]Einzelnachweise
[Bearbeiten | Quelltext bearbeiten]- ↑ a b Jaemoon Yang: Six-Membered Transition States in Organic Synthesis. John Wiley & Sons, 2008, ISBN 978-0-470-19904-6, Diastereoselective Syn-Reduction of β-Hydroxy Ketones, S. 151–155 (google.com).
- ↑ Henning Priepke, Stefan Weigand, Reinhard Brückner: A Butyrolactone → 1,3-Diol Strategy for the Obtention of Tolypothrix Polyethers – Stereoselective Synthesis of a Key Lactone Precursor. In: Liebigs Annalen. 1997. Jahrgang, Nr. 8, 2006, S. 1635–1644, doi:10.1002/jlac.199719970804.
- ↑ Stuart Mickel, Daniel Niederer, Robert Daeffler, Osmani Adman, Ernst Kuesters, Emil Schmid, Karl Schaer, Remo Gamboni: Large-Scale Synthesis of the Anti-Cancer Marine Natural Product (+)-Discodermolide. Part 5: Linkage of Fragments C1-6 and C7-24 and Finale. In: Org. Process Res. Dev. 8. Jahrgang, Nr. 1, 2004, S. 122–130, doi:10.1021/op034134j.
[[Category:Name reactions]]