Differently substituted terminal alkynes that bear sulfonate leaving groups at an appropriate distance were converted in the presence of a propynyl gold(I) precatalyst. After initial formation of a gold acetylide, a cyclization takes place at the β-carbon atom of this species. Mechanistic studies support a mechanism that is related to that of dual gold-catalyzed reactions, but for the new substrates, only one gold atom is needed for substrate activation. After formation of a gold vinylidene complex, which forms a tight contact ion pair with the sulfonate leaving group, recombination of the two parts delivers vinyl sulfonates, which are valuable targets that can serve as precursors for cross-coupling reactions, for example.
A single pass flow diazotization/Mizoroki-Heck protocol has been developed for the production of cinnimoyl and styryl products. The factors that govern aryl diazonium salt stability have been examined in detail leading to the development of a MeOH/DMF co-solvent system in which the diazonium salts can be generated in the presence of all other reaction components and then coupled selectively to give the desired products. Finally the key role of the reaction quench for flow reactions has been demonstrated.
A convenient protocol for the enantioselective synthesis of oxazole a-hydroxy ester derivatives 4 from readily available propargylamides 1 and alkylglyoxylates 3 was developed. The first step of the one-pot procedure is the selective intramolecular in situ formation of an alkylideneoxazoline 2, which then in an intermolecular reaction is enantioselectively transformed to the oxazole a-hydroxy ester derivatives 4 in quantitative yield and good to excellent enantioselectivity via an asymmetric copper(II)-catalyzed Alder-ene reaction.
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.
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