Draw the structural formula for the B-ketoester formed by the Claisen condensation of ethyl butanoate with the following ester

Draw the structural formula for the B-ketoester formed by the Claisen condensation of ethyl butanoate with the following ester. Assume a 1:1 stoichiometry. You do not have to consider stereochemistry. If more than one product is possible, only draw the major product. Do not draw organic or inorganic by-products

The Correct Answer and Explanation is:

Correct Answer:Generated code

O    O
      ||   ||
CH3CH2CH-C-C-O-CH2CH3
      |
      C=O
      |
      O
      |
      

Note: This is a 2D representation. A more common way to draw this structure is:Generated code

O=C-OCH2CH3
      |
CH3CH2CH-C(=O)-OCH2CH3

Which can be written linearly as CH3CH2CH(COOCH2CH3)C(=O)COOCH2CH3

Explanation:

The reaction described is a crossed Claisen condensation between ethyl butanoate and diethyl oxalate. The Claisen condensation is a carbon-carbon bond-forming reaction that occurs between two ester molecules in the presence of a strong base, typically an alkoxide.

1. Identifying the Nucleophile and Electrophile: A successful crossed Claisen condensation requires one ester that can form an enolate (the nucleophile) and one that cannot. Ethyl butanoate (CH₃CH₂CH₂COOEt) has two acidic α-protons on the carbon adjacent to the carbonyl group. In the presence of a base like sodium ethoxide (NaOEt), it will be deprotonated to form a nucleophilic enolate. Diethyl oxalate (EtOOC-COOEt), on the other hand, has no α-protons and therefore cannot form an enolate. It will act as the electrophile. This selectivity ensures that the crossed-condensation product is the major product, minimizing the self-condensation of ethyl butanoate.
2. Reaction Mechanism:
   • Enolate Formation: The ethoxide base removes an α-proton from ethyl butanoate.
   • Nucleophilic Attack: The resulting enolate of ethyl butanoate attacks one of the highly electrophilic carbonyl carbons of diethyl oxalate.
   • Elimination: A tetrahedral intermediate is formed, which then collapses by eliminating the ethoxide group (-OEt) from the oxalate moiety.
3. Product Formation: This sequence of steps results in the formation of a new carbon-carbon bond between the α-carbon of the original ethyl butanoate and the carbonyl carbon of the diethyl oxalate. The final product is a β-ketoester. In this specific case, the product is diethyl 2-ethyl-3-oxobutanedioate. The structure contains the four-carbon backbone from butanoate, which is now substituted at its α-position with an ethoxycarbonyl group originating from the diethyl oxalate.