Youtor
Heck Coupling
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The Heck Reaction is the cross-coupling between an unsaturated halide or triflate and an alkene in the presence of a base and a palladium catalyst. • General features: • 1. The reaction conditions tolerate a wide range of functional groups on the olefin. • 2. The more substituted the olefins is, the slower the reaction proceeds. • 3. The reaction is not sensitive to water but the solvents need to be deoxygenated. • 4. The Heck Coupling is stereospecific. Both the migratory insertion and the hydride elimination proceed with syn stereochemistry. • 5. The active palladium catalyst is generated in situ from precatalysts such as Pd(OAc)2 or Pd(PPh3)4. The reaction is usually conducted in the presence of monodentate or bidentate phosphine ligands and a base. • 6. Substrates with hydrogen atoms on their β-carbons undergo rapid β-hydride elimination to give olefins • 7. Aryl chlorides are not always good substrates because they react very slowly, being I, Br, and OTf best suited. • Reaction mechanism: • 1. Oxidative Addition. • 2. Migratory Insertion (syn). • 3. (C–C bond rotation). • 4. β-hydride elimination (syn). • 5. Reductive Elimination and catalyst regeneration. • Pinterest: • https://www.pinterest.es/pin/67166973... • References: • https://nrochemistry.com/heck-coupling/ • Seminal publications: • 1. J. Am. Chem. Soc. 1968, 90, 5518- 5526. https://doi.org/10.1021/ja01022a034 • 2. J. Org. Chem. 1972, 37, 2320-2322. https://doi.org/10.1021/jo00979a024 • Similar reactions: • Suzuki Coupling: • Suzuki Coupling • Stille Coupling: • Stille Coupling • Sonogashira Coupling: • Sonogashira Coupling
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