The Claisen Ester 
                    The Claisen Ester 
                       Condensation
                       Condensation
         • Esters, like aldehydes and ketones, have 
           acidic -hydrogens.
         • When an ester bearing an -hydrogen is 
           treated with a strong base, a 
           condensation reaction takes place to 
           yield a                -ketoester.
                                              WWU -- Chemistry
                                              WWU -- Chemistry
                        The Claisen Ester 
                        The Claisen Ester 
                            Condensation
                            Condensation
            O
     R CH C O CH CH
           2          2   3
                                                   O       O
            +                NaOCH CH
                                   2   3    R CH C CH C O CH CH
                                                  2                  2  3
            O                                          R
     R CH C O CH CH
           2          2   3                       a  ketoester
                                                        +
      NOTE:  The alkoxide should match the          CH CH O H
      alkyl group of the ester in order to avoid       3  2
      a competing transesterification.
                                                       WWU -- Chemistry
                                                       WWU -- Chemistry
               Claisen Ester Condensation -- 
               Claisen Ester Condensation -- 
                       Mechanism (Part One)
                       Mechanism (Part One)
    1)     O
                                                                               .. _
       CH C OCH                                         O                      :O:
          3       2 5      fast                    _
              +                   HO CH + :CH C OCH                       CH C OCH
                                         2 5           2       2 5           2        2 5
           _ ..
            :O   C H
             ..   2 5                                            enolate ion
            O        acceptor              .. _
    2)                                    :O:
        CH C OCH
           3       2 5                CH C OCH
                              slow       3       2 5
                  O                           O
             _                             CH C OCH
             :CH C    OCH                    2       2 5
                 2       2 5
                   donor
                                                                  WWU -- Chemistry
                                                                   WWU -- Chemistry
             Claisen Ester Condensation -- 
             Claisen Ester Condensation -- 
                    Mechanism (Part Two)
                    Mechanism (Part Two)
             3)      .. _
                    :O:                               :O:
                CH C OCH
                   3        2 5           fast     CH3C
                         O                                  O
                     CH C OCH
                        2        2 5                    CH C OCH
                                                           2       2 5
                                                         +
                                                           _ ..
                                                            :O   CH
                                                             ..    2 5
                                                          WWU -- Chemistry
                                                          WWU -- Chemistry
              The Key to Claisen Ester 
              The Key to Claisen Ester 
                      Condensations
                      Condensations
         • The -carbon of the donor attaches itself 
           to the carbonyl carbon of the acceptor.
         • The alkyl group of the acceptor leaves to 
           form a C=O bond.
                                              WWU -- Chemistry
                                              WWU -- Chemistry