View source for Narasaka–Prasad reduction

The '''Narasaka–Prasad reduction''', sometimes simply called '''Narasaka reduction''', is a [[diastereoselective]] [[reduction (chemistry)|reduction]] of β-hydroxy [[ketone]]s to the corresponding ''syn''-[[diol|dialcohols]]. The reaction employs a boron [[chelating agent]], such as BBu<sub>2</sub>OMe, and a [[reducing agent]], commonly [[sodium borohydride]]. This protocol was first discovered by Narasaka in 1984.<ref name="Book">{{Cite book|first = Jaemoon|last = Yang|chapter-url = https://books.google.com/books?id=A_vUdr6ABGIC&pg=PA151|chapter = Diastereoselective ''Syn''-Reduction of β-Hydroxy Ketones|title = Six-Membered Transition States in Organic Synthesis|year = 2008|publisher = [[John Wiley & Sons]]|pages = 151–155|isbn = 9780470199046}}</ref>
[[File:Narasaka–Prasad reduction.png|thumb|center|400px|Scheme for the Narasaka–Prasad reduction]]
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 NaBH<sub>4</sub> therefore proceeds via an axial attack from the opposite face with respect to the existing [[alcohol (chemistry)|alcohol]].<ref name="Book"/>
[[File:Narasaka–Prasad reduction transition state.png|thumb|center|300px|Transition state for the Narasaka–Prasad reduction showing the reasons for the observed diastereoselectivity]]
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,<ref>{{cite journal |last1= Priepke|first1=Henning |last2=Weigand |first2= Stefan|last3=Brückner|first3=Reinhard|year= 2006|title= A Butyrolactone → 1,3-Diol Strategy for the Obtention of Tolypothrix Polyethers – Stereoselective Synthesis of a Key Lactone Precursor|journal= [[Liebigs Annalen]]|volume= 1997|issue= 8|pages=1635–1644 |doi= 10.1002/jlac.199719970804}}</ref> such as [[discodermolide]]<ref>{{cite journal |last1= Mickel|first1= Stuart|last2=Niederer |first2= Daniel|last3=Daeffler|first3=Robert|last4=Adman|first4=Osmani|last5=Kuesters|first5=Ernst|last6=Schmid|first6=Emil|last7=Schaer|first7=Karl|last8=Gamboni|first8=Remo|year=2004 |title= Large-Scale Synthesis of the Anti-Cancer Marine Natural Product (+)-Discodermolide. Part 5: Linkage of Fragments C1-6 and C7-24 and Finale|journal= [[Org. Process Res. Dev.]]|volume=8 |issue= 1|pages= 122–130|doi=10.1021/op034134j}}</ref>
== See also ==
*[[Evans–Tishchenko reaction]]
== References ==
<references/>
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[[Category:Name reactions]]