The Heck reaction produces a substituted alkene by cross-coupling the alkene with an organohalide in the presence of catalytic palladium. Oxidative addition of the alkyl or aryl halide to the palladium is followed by a syn migratory insertion of the alkene. Bond rotation facilitates a syn β-hydride elimination, and a base-mediated reductive elimination regenerates the catalyst.
- Reagents: Catalytic Palladium, Ligand (e.g. Trialkyl- or Triarylphosphines, etc.), Base (2° or 3° Amine, KOAc, NaOAc, or NaHCO3)
- Reactant: Organohalide [Aryl, Benzyl, Alkenyl, or Alkyl (with no β Hydrogens) and Halide (Cl, Br, I, OTf, OTs, N2+)], Alkene (Alkyl, Aryl, Alkenyl)
- Product: Arylated or Alkenylated Olefin
- Type of Reaction: Pd-Catalyzed Coupling
Lab Tips
- Esters, ethers, carboxylic acids, nitriles, phenols, dienes are well tolerated on the olefin component, but allylic alcohols tend to rearrange.
- Substrates with hydrogens on β-carbons tend to undergo β-hydride elimination affording olefins.
- Aryl chlorides are slow to react, resulting in lower yields.
Mechanism
Top Citations
Original Paper
Related Reactions
- Stille Cross-Coupling
- Olefination
