Coupling Reactions Between sp3 and sp2 Carbon Centers

Selective cross-coupling reactions between C(sp3) and C(sp2) centers had been one of the most difficult tasks in carbon–carbon bond synthesis until the early 1970s, when it was first reported that iron,1,2 nickel,3,4 palladium5 and copper2,6 catalysts are extremely effective for cross-coupling of Grignard reagents with organic halides. Now, nearly 20 years later, transition metal catalyzed cross-coupling has become the reaction of first choice for this purpose.