What products would you expect from the following coupling reactions?
(a)

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Step 1: Identify the type of reaction. This is a coupling reaction involving an aryl halide (bromobenzene) and a Gilman reagent (R2CuLi). Gilman reagents are organocuprates that facilitate the formation of carbon-carbon bonds.

Step 2: Recognize the role of the Gilman reagent. The Gilman reagent donates one of its alkyl groups (R group) to replace the halogen atom (Br) on the aryl halide. This substitution results in the formation of a new C-C bond.

Step 3: Analyze the structure of the reactants. The aryl halide is bromobenzene, and the Gilman reagent is [(CH3CH2CH2CH2)CuLi]2. The alkyl group from the Gilman reagent is a butyl group (CH3CH2CH2CH2).

Step 4: Predict the product. The butyl group from the Gilman reagent will replace the bromine atom on the benzene ring, forming butylbenzene (C6H5CH2CH2CH2CH3).

Step 5: Verify the reaction mechanism. The reaction proceeds via oxidative addition of the aryl halide to the copper center, followed by reductive elimination to form the new C-C bond and release the product.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Coupling Reactions

Coupling reactions are a type of organic reaction where two fragments are joined together, typically involving the formation of a new carbon-carbon bond. These reactions are crucial in organic synthesis for constructing complex molecules. Common examples include the Suzuki and Sonogashira reactions, which utilize palladium or copper catalysts to facilitate the coupling of aryl or vinyl halides with nucleophiles.

Organocuprates

Organocuprates, such as the reagent shown in the question (R2CuLi), are organometallic compounds that contain a carbon atom bonded to a copper atom. They are highly nucleophilic and are often used in coupling reactions to react with electrophiles, such as alkyl or aryl halides. Their ability to form stable carbon-carbon bonds makes them valuable in synthetic organic chemistry.

Electrophilic Aromatic Substitution

Electrophilic aromatic substitution (EAS) is a fundamental reaction mechanism in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. In the context of the question, the bromobenzene acts as an electrophile, and the organocuprate can facilitate the substitution process, leading to the formation of a new carbon-carbon bond on the aromatic system. Understanding EAS is essential for predicting the products of reactions involving aromatic compounds.

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