organolithium reagent

An organolithium reagent is a close cousin of the Grignard reagent, and an even more aggressive one. It is a molecule with a carbon-lithium bond, R-Li, where the carbon again carries a large partial negative charge and behaves as a strong carbon nucleophile and a very powerful base. Think of it as a Grignard turned up to maximum.

Lithium is even less electronegative than magnesium, so the C-Li bond is even more polarized toward carbon; the carbon is even more carbanion-like and more reactive. You make an organolithium (such as n-butyllithium, n-BuLi) by treating an alkyl or aryl halide with lithium metal, and like Grignards they must be handled under dry, inert conditions because they react explosively with water and air. Their carbon attacks carbonyl groups just as Grignards do, adding to aldehydes and ketones to build alcohols. Two practical differences matter: organolithiums are often more reactive and less hindered, so they will add to bulky ketones that resist Grignards, and they are extremely strong bases, frequently used not as carbon nucleophiles but purely to rip off a proton and make another carbanion or enolate.

Organolithiums are everywhere in synthesis: n-BuLi is a standard reagent for deprotonations and for making other organometallics by lithium-halogen exchange, and bulky lithium amide bases like LDA are made from them. The same property that makes them useful, ferocious reactivity, also makes them hazardous: alkyllithium solutions can ignite on contact with air, so they demand careful, dry, cold, inert-atmosphere technique.