lecture 4

• 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