title: Rhodium- and palladium-catalyzed 1,5-substitution reactions of 2-en-4-yne acetates and carbonates with organoboronic acids.
abstract: Two methods involving the rhodium-catalyzed reaction of 2-en-4-yne acetates and the palladium-catalyzed reaction of 2-en-4-yne carbonates with organoboronic acids were investigated; both afforded exclusively the (E)-configured vinylallenes. The coordinative interaction of the rhodium with the acetate group promoted the δ-elimination of Rh(I)-OAc from the alkenylrhodium intermediate II in both syn and anti modes, with the syn-elimination being the major path. DFT calculations revealed that a conformer of this intermediate (II), which can lead to the (E)-configured vinylallene product via the syn-elimination mode, is energetically the most favorable conformer. The rhodium-catalyzed procedure is not applicable to reactions involving (E)-configured enyne acetates, because the geometry of the alkenylrhodium intermediate that is derived from the corresponding (E)-enyne acetate would not allow such coordinative interaction to occur. The palladium-catalyzed method, which proceeds through formation of the σ-vinylallenylpalladium intermediate, B, is suitable for both the (E)- and (Z)-configured enyne carbonates and appears to have a wider scope for both organoboronic acids and enyne substrates. The palladium-catalyzed reaction of an enantiomerically enriched enyne carbonate proceeded with racemization.
authors.affiliation: Department of Chemistry, Faculty of Science, Izmir Institute of Technology, Urla 35430, Izmir, Turkey.
authors.forename: Muhammed
authors.initials: M
authors.lastname: Üçüncü
authors.forename: Erman
authors.initials: E
authors.lastname: Karakuş
authors.forename: Melih
authors.initials: M
authors.lastname: Kuş
authors.forename: Gürkan Eray
authors.initials: GE
authors.lastname: Akpınar
authors.forename: Özge
authors.initials: Ö
authors.lastname: Aksın-Artok
authors.forename: Norbert
authors.initials: N
authors.lastname: Krause
authors.forename: Sıla
authors.initials: S
authors.lastname: Karaca
authors.forename: Nuran
authors.initials: N
authors.lastname: Elmacı
authors.forename: Levent
authors.initials: L
authors.lastname: Artok