Predict the major products of the following crossed Claisen condensations.
(a)

Verified step by step guidance

1. Step 1: Understand the Claisen condensation reaction. A Claisen condensation involves the reaction between two esters or one ester and a ketone in the presence of a strong base, typically an alkoxide, to form a β-keto ester or β-diketone. Crossed Claisen condensations occur between two different esters or an ester and a ketone.
2. Step 2: Identify the reactants in the crossed Claisen condensation. Determine which compounds are involved in the reaction and note their functional groups (e.g., ester or ketone). This will help predict the nucleophile and electrophile in the reaction.
3. Step 3: Determine the nucleophile. The nucleophile is typically the enolate ion formed from the compound with the most acidic α-hydrogen. Use the base to deprotonate the α-hydrogen adjacent to the carbonyl group, forming the enolate ion. Represent this step using MathML: ${\mathrm{CH}}_2\left(\mathrm{COOR}\right)-\to {\mathrm{CH}}_2\left(\mathrm{COOR}\right)-$
4. Step 4: Identify the electrophile. The electrophile is the carbonyl carbon of the other ester or ketone. The enolate ion attacks the electrophilic carbonyl carbon, leading to the formation of a new C-C bond. Represent this step using MathML: $R-\mathrm{COOR}\to R-\mathrm{CO}(\mathrm{CH}-\mathrm{COOR})$
5. Step 5: Predict the major product. After the nucleophilic attack, the intermediate undergoes protonation and elimination of the alkoxide group to form the final β-keto ester or β-diketone product. Consider steric and electronic factors to predict the major product of the reaction.

Key Concepts

Claisen Condensation

Claisen condensation is a reaction between two esters or an ester and a carbonyl compound in the presence of a strong base, typically sodium ethoxide. This reaction results in the formation of a β-keto ester or a β-diketone. Understanding this mechanism is crucial for predicting the products, as it involves nucleophilic attack and subsequent elimination of an alcohol.

Crossed Claisen Condensation

Crossed Claisen condensation refers to a variation of the Claisen reaction where two different carbonyl compounds are used. This can lead to a mixture of products, making it essential to consider the reactivity and sterics of the reactants. The major product is typically the one formed from the more reactive ester or carbonyl compound, which can help in predicting the outcome of the reaction.

Regioselectivity

Regioselectivity in organic reactions refers to the preference of a chemical reaction to occur at one location over another in a molecule. In the context of crossed Claisen condensations, understanding which carbonyl compound is more likely to react and where the nucleophilic attack will occur is vital for predicting the major product. Factors such as steric hindrance and electronic effects play significant roles in determining regioselectivity.