Grignard Reaction Scheme MeMgBr OH N C Me Me H THF, 0 °C
The Correct Answer and Explanation is :
The given reaction scheme involves a Grignard reaction, where methylmagnesium bromide (MeMgBr) is used as the Grignard reagent in the presence of tetrahydrofuran (THF) at 0°C. Let’s break down the reaction step by step.
Step 1: Identifying the Reactants
- Grignard Reagent (MeMgBr): This is a strong nucleophile and a strong base, known for attacking electrophilic carbonyl compounds.
- Substrate: The given structure appears to have an amide (-N-C=O) functional group.
- Solvent: THF, a common solvent for Grignard reactions, stabilizes the organomagnesium reagent.
- Temperature: 0°C suggests controlled reaction conditions to avoid side reactions.
Step 2: Understanding the Reaction Mechanism
- Attack on the Amide Carbonyl:
- Grignard reagents typically react with esters, ketones, and aldehydes to form alcohols.
- However, with amides, Grignard reagents do not directly yield alcohols. Instead, they replace the amide nitrogen with two equivalent alkyl groups.
- The lone pair on nitrogen delocalizes, making the carbonyl carbon less reactive than aldehydes or ketones, but it can still react under excess Grignard conditions.
- Formation of a Ketone Intermediate:
- The first equivalent of MeMgBr attacks the carbonyl carbon, causing elimination of NR₂ and forming a ketone intermediate.
- Further Reaction to a Tertiary Alcohol:
- The ketone undergoes a second attack by another MeMgBr equivalent, leading to a tertiary alcohol after acidic workup.
Step 3: Final Product
The reaction produces a tertiary alcohol at the carbon center that was originally the amide carbonyl. The structure of the product will have:
- Three alkyl groups attached to the central carbon.
- A hydroxyl (-OH) group in place of the original amide.
Thus, the final product is 2-methyl-2-pentanol (tertiary alcohol with three alkyl groups attached to the hydroxyl carbon).