Question

Given the following information, why don't chemists just use butyllithium itself to deprotonate the aldehyde or ketone and form the enolate?

Enolates are frequently formed by treating an aldehyde or ketone with LDA. However, the LDA must first be generated by reacting diisopropylamine with butyllithium.

Answer 1

`Bu^(n)Li` is a powerful base, but also a powerful nucleophile.

Explanation:

`Bu^(n)Li` and `MeLi` might add to the carbonyl carbon, rather than deprotonating the `alpha` hydrogen. On the other hand, `LDA` is a powerful base, but an indifferent nucleophile. The action of `LDA` on the `alpha`-hydrogen will generate the enolate.