Question

Question: As we learned in Chapter 20, organolithium reagents (RLi) are strong bases that readily react with acidic protons. Why aren’t organolithium reagents used to generate enolates?

Short answer

Answer

Organolithium reagents are nucleophiles with a strong base. By using them in reactions containing carbonyl groups, they can undergo enolizations as well as take part in a nucleophilic attack. Thus, the yield of enolates decreases.

So, it preferred to use those reagents that act only as a base, for example, LDA and NaH.

Step-by-step solution

Function of organolithium reagents

Organolithium reagents function both as a nucleophile and a base. They function as a nucleophile when there is a possibility of a nucleophilic attack, while they function as a base when strong acidic protons are present. When a carbonyl group is present, they tend to function both as a nucleophile and a base.

Representation of RLi acting both as a nucleophile and a base

 Step 2: Preferred reagents for enolate formation

Reagents that function only as a base are found to be more suitable for enolate formation.

Representation of an enolate formation by the addition of a base

Based on the steps mentioned, it is clear that organolithium reagents are nucleophiles with a strong base. By using them in reactions containing carbonyl groups, they can undergo enolizations as well as take part in a nucleophilic attack. Thus, the yield of enolates decreases.

So, it preferred to use those reagents that act only as a base, for example, LDA and NaH.