Organolithium Reagents

A representative example — structures drawn live.

What they are and how they form

An organolithium reagent has a carbon–lithium bond, R–Li. It is made by treating an alkyl or aryl halide with two equivalents of lithium metal in a dry, inert solvent: R–X + 2 Li → R–Li + LiX. Common examples are n-butyllithium (n-BuLi), methyllithium, and phenyllithium.

As with Grignards, the bond is strongly polarized toward carbon because lithium is very electropositive. In fact the C–Li bond is even more ionic than the C–Mg bond, so the carbon carries more carbanion character. That single difference — more ionic, more carbanion-like carbon — explains why organolithiums are both stronger nucleophiles and stronger bases than the corresponding Grignard reagents.

Carbonyl additions, just like Grignards

Organolithiums add to carbonyl compounds exactly the way Grignards do, forming a new C–C bond and, after acidic workup, an alcohol:

• Formaldehyde → primary alcohol
• Other aldehydes → secondary alcohol
• Ketones → tertiary alcohol

Because they are more reactive, organolithiums often succeed where a Grignard stalls. In particular, they add to sterically hindered ketones that resist bulky Grignard reagents, making R–Li the reagent of choice for congested targets.

The special reaction: carboxylic acids to ketones

Here is the standout difference. A Grignard reagent simply gets deprotonated by a carboxylic acid's O–H and does nothing else. Organolithiums, thanks to their extra reactivity, do more. The first equivalent deprotonates the acid to give a carboxylate, and then a second equivalent of R–Li adds to the carboxylate carbon to form a stable dianion (a gem-diolate). That dianion survives in solution; it only collapses to a carbonyl during the aqueous workup, releasing a ketone.

This is a genuinely useful, distinctive transformation: carboxylic acid + 2 R–Li, then H₃O⁺ → ketone. Grignards cannot do it.

Making Gilman reagents for softer chemistry

Sometimes the raw power of an organolithium is a liability — for example, when you want to add to only part of a molecule or do a conjugate (1,4) addition rather than direct (1,2) addition. Treating two equivalents of R–Li with a copper(I) salt (CuI) gives a lithium dialkylcuprate, R₂CuLi, known as a Gilman reagent.

Gilman reagents are much softer, more selective nucleophiles. They perform reactions organolithiums and Grignards handle poorly — coupling with alkyl and vinyl halides, and clean 1,4-conjugate additions to α,β-unsaturated carbonyls — while leaving the more reactive carbonyl carbon alone. Organolithiums are thus both a reagent in their own right and a gateway to cuprate chemistry.

Handling: even more sensitive than Grignards

Every caution that applies to Grignards applies more strongly here. Organolithiums are violently reactive toward water and any protic hydrogen — O–H, N–H, terminal alkyne C–H — all of which simply protonate the reagent to R–H. Many are also pyrophoric (they ignite on contact with air), so they are handled under nitrogen or argon with rigorously dry solvents and syringe technique. The acidic workup is always the final step.

When to pick R–Li over R–MgX

Default to a Grignard for routine carbonyl additions — it is cheaper and easier to handle. Reach for an organolithium when you need extra reactivity: adding to a hindered ketone, converting a carboxylic acid directly into a ketone, or generating a Gilman reagent for conjugate addition or cross-coupling. The trade-off is greater sensitivity and the need for strict air-free technique.