What product is formed when 3-methyl-2-cyclohexenone reacts with each of the following reagents?
a. CH₃MgBr followed by H₃O⁺
b. (CH₃CH₂)₂CuLi followed by H₃O⁺

Verified step by step guidance

1. Step 1: Analyze the structure of 3-methyl-2-cyclohexenone. It is a conjugated enone, meaning it has both a carbonyl group (C=O) and a double bond in conjugation. This makes it susceptible to both nucleophilic addition at the carbonyl carbon and conjugate (1,4) addition at the β-carbon of the double bond.
2. Step 2: For part (a), CH3MgBr is a Grignard reagent, which is a strong nucleophile. Grignard reagents typically perform nucleophilic addition to the carbonyl carbon (1,2-addition). The CH3 group from CH3MgBr will attack the carbonyl carbon, breaking the C=O double bond and forming an alkoxide intermediate. Upon protonation with H3O+, the alkoxide is converted into an alcohol.
3. Step 3: For part (b), (CH3CH2)2CuLi is a Gilman reagent, which is a softer nucleophile. Gilman reagents preferentially perform conjugate (1,4) addition to α,β-unsaturated carbonyl compounds. The ethyl group (CH3CH2) will add to the β-carbon of the conjugated double bond, shifting the double bond and leaving the carbonyl group intact. Protonation with H3O+ completes the reaction.
4. Step 4: Draw the product for part (a). After the 1,2-addition of CH3MgBr and subsequent protonation, the product will have a new CH3 group attached to the former carbonyl carbon, and the carbonyl group will be converted into an alcohol.
5. Step 5: Draw the product for part (b). After the 1,4-addition of (CH3CH2)2CuLi and subsequent protonation, the product will have a new CH2CH3 group attached to the β-carbon of the conjugated system, with the carbonyl group remaining intact.

Key Concepts

Nucleophilic Addition

Nucleophilic addition is a fundamental reaction in organic chemistry where a nucleophile attacks an electrophilic carbon atom, typically in a carbonyl group. In the case of 3-methyl-2-cyclohexenone, the carbonyl carbon is susceptible to nucleophilic attack, leading to the formation of an alcohol after subsequent protonation. Understanding this mechanism is crucial for predicting the products of reactions with reagents like Grignard reagents and organocuprates.

Grignard Reagents

Grignard reagents, such as CH3MgBr, are highly reactive organomagnesium compounds that act as strong nucleophiles. They can add to carbonyl compounds, forming a new carbon-carbon bond. After the addition, hydrolysis with H3O+ converts the intermediate alkoxide into an alcohol. Recognizing the reactivity and behavior of Grignard reagents is essential for determining the outcome of the reaction with 3-methyl-2-cyclohexenone.

Organocuprates

Organocuprates, like (CH3CH2)2CuLi, are less reactive than Grignard reagents but still serve as nucleophiles in organic reactions. They can add to carbonyl compounds, leading to the formation of ketones or aldehydes, depending on the structure of the starting material. Understanding the unique properties and selectivity of organocuprates is important for predicting the products formed when they react with compounds like 3-methyl-2-cyclohexenone.