lecture 4

    Cards (7)

    • NaBH4- 1,4 addition-
      -nucleophilic electrons in B-H bonds diffuse
      -makes it a soft nucleophile
    • NaBH4/CeCl3- 1,2 addition
      CeCl3 is a lewis acid
      it coordinates to the carbonyl carbon activating it to nucleophilic attack
    • BH3- reduction reagent

      -Good reagent for unreactive carbonyls
      -exists as gaseous B2H6
      -Can be made into liquid by complexation with Et2O, THF
    • DIBAL-H(reduction)

      -Structural similarities to LiAlH4 and BH3
      -Milder reducing agent than LiAlH4, reduces nitriles to aldehydes
    • DIBAL-H most useful reaction

      esters to aldehydes
      -possible because the tetrahedral intermediate formed is stable at low temperatures
      -followed by higher temp collapsing intermediate and 2nd addition of hydride
    • Ester to aldehyde difficulty(reduction)

      -requires two steps
      -aldehydes are more reactive than esters
      LiAlH4 followed by PDC
    • LiBH4 Reduction

      -Reduces esters to alcohols
      -not as powerful as LiAlH4- wont reduce carboxylic acids to alcohols
      -different selectivity to BH3