Buchwald–Hartwig amination

The Buchwald–Hartwig amination is the Suzuki coupling's cousin for nitrogen: instead of bonding a carbon to an aromatic ring, it bonds a nitrogen, joining an amine directly to an aryl halide. It gave chemists a general, mild way to attach amines to aromatic rings, a transformation that was clumsy and harsh by older methods.

Like other cross-couplings it runs on a palladium catalyst, with the amine and a base replacing the boron partner of a Suzuki reaction. The key enabler was a generation of bulky, electron-rich phosphine ligands (often associated with the Buchwald and Hartwig groups) that let the catalyst grip difficult substrates and turn over efficiently, expanding the range of amines and aryl halides that couple cleanly.

Because aryl–amine bonds and the nitrogen-containing rings they help build are extremely common in drugs, this reaction is a staple of modern medicinal chemistry and pairs naturally with parallel synthesis for making analog series. Practical caveats mirror those of other Pd couplings: choosing the right ligand and base for a given pair, controlling competing side reactions, and scrubbing residual palladium from the product.