Cyclisierung von Goldacetyliden: Synthese von Vinylsulfonaten über Vinylidengold‐Komplexe

Abstract

Verschieden substituierte terminale Alkine mit Sulfonat-Abgangsgruppen in passender Entfernung wurden in Gegenwart von Propinylgold(I)-Präkatalysatoren umgesetzt. Nach der Bildung eines Goldacetylids findet eine Cyclisierung über das b-Kohlenstoffatom des Goldacetylids statt. Der Mechanismus dürfte ähnlich zu dem der dualen Goldkatalyse sein, aber im Fall der neuen Substrate wird nur ein Goldzentrum für die Aktivierung des Substrates bençtigt. Nach Bildung eines Vinylidengold-Komplexes, der ein enges Kontaktionenpaar mit der Sulfonat-Abgangsgruppe bildet, liefert eine Rekombination der beiden Teile Vinylsulfonate, die wertvolle Zielverbindungen sind und z. B. als Vorstufen in Kreuzkupplungen fungieren kçnnen. Schema 1. Oben: dualer Aktivierungsweg zu Vinylidenen; unten: geplante Acetylid-und-Abgangsgruppen-Strategie als Weg zu Vinylidenen.

Gold(I) Vinylidene Complexes as Reactive Intermediates and Their Tendency to π‐Backbond

“…These three transition states reflect different conformations and are based on three energetically close‐lying conformations of the starting complexes Ia – c . For the two energetically more favourable transition states, we identified the tight ion pairs IIa and IIb as subsequent intermediates which have been proposed previously . Both intermediates are energetically high lying (9.8 and 10.9 kcal mol −1 ).…”

“…These reactions are thought to proceed via a common intermediate (Scheme , top) . In addition, vinylidene intermediates have been proposed in the preparation of vinyl sulfonates, where they are expected to be formed as a tight ion pair (Scheme , bottom) …”

Double Gold Activation of 1‐Ethynyl‐2‐(Phenylethynyl)Benzene Toward 5‐exo‐dig and 6‐endo‐dig Cyclization Reactions

“…Most remarkable about the generated gold(I) vinylidene complexes is their ability to insert into unactivated alkyl C(sp 3 )−H bonds with excellent regioselectivity, which allows the formation of two additional rings in one, single, catalytic reaction. Although all efforts to stabilize the gold(I) vinylidene intermediates failed, by switching to other transition metals with better back‐donating properties, the new reactivity pattern could be experimentally confirmed by the isolation of heterobimetallic vinylidene ruthenium/vinyl gold species and the principles could be extended to the reaction of gold(I) acetylides with other electrophiles …”

On the Gold‐Catalyzed Generation of Phenyl Cations from 1,5‐Diynes

“…[3a-e,h,j,k,o,p] These highly electrophilic species were shown to react evenw ith unactivated C(sp 2 )-H as wella sC ( sp 3 )-H bonds.D epending on the backbone,a6-endo-dig pathway via the a-carbon atom is also possible (Scheme 1, bottom left). [5] Recently we could show that diyne systems can also serve as starting materials even if only one gold centre is present. [5] Recently we could show that diyne systems can also serve as starting materials even if only one gold centre is present.…”