A β-keto ester is the product of which of the following reactions?

Question

BlackTom AI · Accepted Answer

A Claisen condensation generates β‑keto esters by coupling two ester molecules (or an ester and a ketone) through enolate formation, nucleophilic attack at a carbonyl, and loss of an alkoxide leaving group.

Relevant concepts
1. Enolate chemistry: bases deprotonate the α‑carbon of an ester to give an enolate nucleophile. 2. Nucleophilic acyl substitution: the enolate attacks another ester’s carbonyl, forming a tetrahedral intermediate that collapses to expel an alkoxide, producing a β‑keto ester. 3. Reaction control: the base is the alkoxide matching the ester’s alcohol (e.g., EtO– for ethyl esters) to prevent transesterification.

Step‑by‑step mechanism (generic Claisen, intermolecular)
1) Base (RO–) deprotonates the α‑hydrogen of an ester (R′COCH2OR) to form the stabilized enolate: R′COCH–OR ↔ R′COCH= O–.  
2) The enolate attacks the carbonyl carbon of a second ester molecule (R″COOR), creating a tetrahedral alkoxide intermediate.  
3) The tetrahedral intermediate collapses, expelling the alkoxide RO– as the leaving group and forming the β‑keto ester R′COCH2COR″.  
4) Protonation (workup) yields the neutral β‑keto ester product (for example, ethyl acetate → ethyl acetoacetate under self‑Claisen conditions).

Why the Claisen condensation is correct
The defining product of a Claisen condensation is a β‑keto ester (or a 1,3‑dicarbonyl when a ketone is involved). The mechanism and required reagents match the production of β‑keto esters directly.

Why the other choices are incorrect
- Robinson annulation: sequence of Michael addition followed by intramolecular aldol/cyclization that yields cyclohexenone derivatives, not β‑keto esters.  
- Aldol condensation: gives β‑hydroxy carbonyls or α,β‑unsaturated carbonyls after dehydration (β‑hydroxy ketone/aldehyde → enone), not esters.  
- Dieckmann condensation: this is an intramolecular (ring‑closing) variant of the Claisen that produces cyclic β‑keto esters specifically; it is a special case but the classic product type named in the choices is generated by the Claisen.  
- Michael addition: gives 1,4‑addition products to α,β‑unsaturated carbonyls, not β‑keto esters.

Conclusion
The correct choice is D) a Claisen condensation, which directly produces β‑keto esters. This matches the provided answer.

A β-keto ester is the product of which of the following reactions?单项选择题

类似问题

A Claisen condensation is given below. Based on the numbering of reactant carbons, assign numbers to the lettered carbons in the product.

Which of these could be a nucleophile for a Claisen Condensation? (select all that apply)

The Claisen condensation first forms an ion which undergoes a to give the beta-ketoester. This product immediately undergoes an acid base reaction because it's pKa is about which is favored over the ester who's pKa is about .

The Claisen condensation is analogous to the reaction of aldehydes but with esters.

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