Chapter 14: Organometallic Compounds

Reactions of RC≡CM with Aldehydes and Ketones

Reaction type:  Nucleophilic Addition

Summary

• Acetylide 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.
• Note the similarity to the reactions of RLi and RMgX

 

• Reaction of RLi and RMgX with aldehydes and ketones
• Reaction of RLi and RMgX with epoxides
• Reaction of RLi and RMgX with carbon dioxide

NUCLEOPHILIC ADDITION OF RC≡CMgX TO AN ALDEHYDE
Step 1: The nucleophilic C in the organometallic reagent adds to the electrophilic C in the polar carbonyl group, electrons from the C=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.

© Dr. Ian Hunt, Department of Chemistry