Palladium in Heterocyclic Chemistry 23Cross-coupling reactions between organometallic species and halides
(sometimes trifl ates) – making carbon–carbon bonds
The overall conversion can be summarised as follows:
The organometallic components (RM) are often prepared by an exchange reaction with an organolithium (see indi-
vidual chapters for the generation of heterocyclic lithium reagents) and also, for boron and tin, by palladium-catalysed
methods, as illustrated for selected examples below. Note: Organolithium compounds do not perform well in cross-
coupling reactions.
Boronic acid couplings (Suzuki–Miyaura reaction)
This reaction is the most important of the cross-coupling reactions and is widely used for production of fi ne chemi-
cals, such as pharmaceuticals. All variations of this reaction are equally useful: Het^1 B(OH) 2 Het^2 X→ Het^1 - Het^2 ,
ArB(OH) 2 HetX → Ar-Het and HetB(OH) 2 ArX → Het-Ar. Either a free boronic acid or an ester can be used.
The inclusion of a mild base is essential for these couplings.