Reactions of RMgX and RLi with aldehydes and ketones

Reactions of RLi and RMgX with Aldehydes and Ketones

 

Reactions usually in Et₂O or THF followed by H₃O⁺ work-ups

Reaction type:  Nucleophilic Addition

Summary

• Organolithium or Grignard reagents react with the carbonyl group, C=O, in aldehydes or ketones to give alcohols.
• The substituents on the carbonyl dictate the nature of the product alcohol.
• Addition to methanal (formaldehyde) gives primary alcohols.
• Addition to other aldehydes gives secondary alcohols.
• Addition to ketones gives tertiary alcohols.
• The acidic work-up converts an intermediate metal alkoxide salt into the desired alcohol via a simple acid base reaction.

NUCLEOPHILIC ADDITION OF RLi or RMgX TO AN ALDEHYDE
Step 1: The nucleophilic C in the organometallic reagent adds to the electrophilic C in the polar carbonyl group, electrons from theC=O move to the electronegative O creating an intermediate metal alkoxide complex.
Step 2: This is the  work-up step, a simple acid/base reaction. Protonation of the alkoxide oxygen creates the alcohol product from the intermediate complex.