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Heck Coupling

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