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Concept
Réaction de Heck
Résumé
The Heck reaction (also called the Mizoroki–Heck reaction) is the chemical reaction of an unsaturated halide (or triflate) with an alkene in the presence of a base and a palladium catalyst to form a substituted alkene. It is named after Tsutomu Mizoroki and Richard F. Heck. Heck was awarded the 2010 Nobel Prize in Chemistry, which he shared with Ei-ichi Negishi and Akira Suzuki, for the discovery and development of this reaction. This reaction was the first example of a carbon-carbon bond-forming reaction that followed a Pd(0)/Pd(II) catalytic cycle, the same catalytic cycle that is seen in other Pd(0)-catalyzed cross-coupling reactions. The Heck reaction is a way to substitute alkenes.
The original reaction by Tsutomu Mizoroki (1971) describes the coupling between iodobenzene and styrene in methanol to form stilbene at 120 °C (autoclave) with potassium acetate base and palladium chloride catalysis. This work was an extension of earlier work by Fujiwara (1967) on the Pd(II)-mediated coupling of arenes (Ar–H) and alkenes and earlier work by Heck (1969) on the coupling of arylmercuric halides (ArHgCl) with alkenes using a stoichiometric amount of a palladium(II) species.
In 1972 Heck acknowledged the Mizoroki publication and detailed independently discovered work. Heck's reaction conditions differ in terms of the catalyst (palladium acetate), catalyst loading (0.01 eq.), base (hindered amine), and absence of solvent.
In 1974 Heck showed that phosphine ligands facilitated the reaction.
The reaction is catalyzed by palladium complexes. Typical catalysts and precatalysts include tetrakis(triphenylphosphine)palladium(0), palladium chloride, and palladium(II) acetate. Typical supporting ligands are triphenylphosphine, PHOX, and BINAP. Typical bases are triethylamine, potassium carbonate, and sodium acetate.
The aryl electrophile can be a halide (Br, Cl) or a triflate as well as benzyl or vinyl halides. The alkene must contain at least one sp2-C-H bond. Electron-withdrawing substituents enhance the reaction, thus acrylates are ideal.
Source officielle
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