title: Suzuki-Miyaura Cross-Coupling Reactions of Highly Fluorinated Arylboronic Esters: Catalytic Studies and Stoichiometric Model Reactions on the Transmetallation Step.
abstract: 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. PdIIcomplexes 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-C5NF4or [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.
authors.affiliation: Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, 12489, Berlin, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Kohlmann
authors.affiliation: Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, 12489, Berlin, Germany.
authors.forename: Thomas
authors.identifier: http://orcid.org/0000-0003-1629-5352
authors.initials: T
authors.lastname: Braun
authors.affiliation: Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, 12489, Berlin, Germany.
authors.forename: Reik
authors.initials: R
authors.lastname: Laubenstein
authors.affiliation: Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, 12489, Berlin, Germany.
authors.forename: Roy
authors.initials: R
authors.lastname: Herrmann
keywords: boron; cross-coupling; fluorine; palladium; transmetallation