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The Claisen Condensation

The nucleophilic carbon of the enolate ion adds to the electrophilic carbon of a molecule of ethyl acetate that has not been deprotonated. A carbon-carbon bond is formed. The reaction produces yet another tetrahedral intemediate as shown in Equation 1.
Exercises about Claisen condensation
Since the newly formed tetrahedral center has an electronegative atom attached to it, reformation of the carbonyl group, as shown in Equation 2, is a reasonable process.
Exercises about Claisen condensation

         Exercise 1 

Draw the structure of the major product you would expect to be formed in each of the following situations:
Exercises about Claisen condensation



        Exercise 3:

An intramolecular version of the Claisen condensation is known as the Dieckmann condensation. Equation 3 shows how this reaction was put to good use as part of the total synthesis of the prostaglandin PGA2.
Exercises about Claisen condensation

Equation 4 offers another example of the Dieckmann condensation that was involved in the synthesis of tropinone, a degradation product that was produced during the determination of the structure of the physiologically active alkaloid atropine.
Exercises about Claisen condensation

An early synthesis of cholesterol involved the "mixed Claisen reaction" shown if Equation 5.

      Example 4  :Dieckmann Condensation



Exercises about Claisen condensation

      Example 5 :Crossed Claisen Condensation



Exercises about Claisen condensation

     Example 6:

The classic Claisen condensation, a self-condensation between two molecules of a compound containing an enolizable ester.
Exercises about Claisen condensation

Example 7:

The mixed (or "crossed") Claisen condensation, where one enolizable ester or ketone and one nonenolizable ester are used.
Exercises about Claisen condensation

Example  8:

The Dieckmann condensation, where a molecule with two ester groups reacts intramolecularly, forming a cyclic β-keto ester. In this case, the ring formed must not be strained, usually a 5- or 6-membered chain or ring.
Exercises about Claisen condensation

Example 9:


The Stobbe condensation [5] is a modification specific for the diethyl ester of succinic acid requiring less strong bases.[6]An example is its reaction with benzophenone:[7]
Stobbe condensation
A reaction mechanism that explains the formation of both an ester group and a carboxylic acid group is centered around alactone intermediate (5):
Stobbe condensation mechanism

Example 10:


Exercises about Claisen condensation

Example 11:

Exercises about Claisen condensation
Exercises about Claisen condensation  

Example 12:

Exercises about Claisen condensation


Exercises about Claisen condensation

Example 13:

Exercises about Claisen condensation

Example 14:

Exercises about Claisen condensation

Example 15:

Exercises about Claisen condensation                                                                           

Example 16:


Exercises about Claisen condensation

Example 17:


Exercises about Claisen condensation

Example 18:


Exercises about Claisen condensation




tác giả

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