Chemistry - A European Journal
Chemistry - A European Journal
5 years ago

Suzuki–Miyaura Cross-Coupling Reactions of Highly Fluorinated Arylboronic Esters: Catalytic Studies and Stoichiometric Model Reactions on the Transmetallation Step

Suzuki–Miyaura Cross-Coupling Reactions of Highly Fluorinated Arylboronic Esters: Catalytic Studies and Stoichiometric Model Reactions on the Transmetallation Step
Reik Laubenstein, Thomas Braun, Johannes Kohlmann, Roy Herrmann
Fluorinated 4-aryl phenylalanine amino acid derivatives (aryl=2-C5NF4, 4-C6H4SF5, 2-C6H4SCF3, C6F5) were obtained in Suzuki–Miyaura cross-coupling reactions of phenylalanine precursors with highly fluorinated aryl boronic acid and esters in the presence of CsF. PdII complexes that possessed phenyl alanine derived ligands, such as trans-[PdBr{4-C6H4CH2CH{NHC(O)CH3}CO2Et}(PiPr3)2], were used as catalysts. Stoichiometric model reactions indicate the intermediate generation of the boronate Cs[BF(2-C5NF4)(pin)] (pin=pinacolato=O2C2Me4). The transmetallation step with Cs[BF(4-C6H4SF5)(pin)], [NMe4][BF(2-C5NF4)(pin)] and/or the fluorido complex trans-[PdF{4-C6H4CH2C{NHC(O)CH3}(CO2Et)2}(PiPr3)2] was investigated. A comparison of the reactions of trans-[PdX{4-C6H4CH2C{NHC(O)CH3}(CO2Et)2}(PiPr3)2] (X=Br, F) with 2-Bpin-C5NF4 or [NMe4][BF(2-C5NF4)(pin)] revealed the remarkable high reactivity of the fluorido complex towards 2-BpinC5NF4. Low-temperature NMR studies indicated the ionic species trans-[Pd{4-C6H4CH2C{NHC(O)CH3}(CO2Et)2}(PiPr3)2][BF(2-C5NF4)(pin)] to be a highly reactive intermediate. Deserves a metal: The Suzuki–Miyaura cross-coupling reaction of highly fluorinated boronic esters, such as 2-Bpin-C5NF4, was investigated by using [Pd(Me)2(tmeda)] or trans-[PdBr{4-C6H4CH2CH{NHC(O)CH3}CO2Et}(PiPr3)2] as precatalysts. Stoichiometric studies on the transmetallation step revealed the high reactivity of a Pd fluorido derivative towards 2-BpinC5NF4, which leads to the formation of an ionic intermediate and finally yields the cross-coupling product.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201700549

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