lecture 8

• Nucleophilic addition to carbonyls

  -nucleophiles add to carbonyls forming a tetrahedral intermediate

  -intermediate collapses generating new carbonyl and leaving group

  -good - x=esters, acid chlorides

  -bad- x= alkyl or H
• Cannizzaro Reaction


  -Hydride is the leaving group

  -aldehyde heated with hydroxide ion, disproportionation occurs

  -yields a carboxylic acid and an alcohol

  -aldehyde must not posses any alpha hydrogens
• NADPH

  -Natures most important reducing agent

  -hydride donor

  -catalysed by an enzyme
• NADPH Reduction enzyme


  -ensures only s isomer of lactic acid formed

  -binds to NADPH and pyruvic acid to ensure hydride delivered to only one face of the carbonyl
• Tishchenko reaction


  -conversion of aldehydes into esters in the presence of a lewis acid catalyst
• Aldol-Tischenko

  -products of an aldol condensation are reduced by an aldehyde

  -6 membered transition state where metal ion chelates both oxygens ensures the anti-arrangement of the 1,3 diol

  -with chiral lewis acid catalysts, reaction can be made enantioselective