Quinones exhibit orthogonal ground- and excited-state reactivities and are therefore highly suitable organocatalysts for the development of sequential catalytic processes. Herein, the discovery of an anthraquinone-catalyzed thermal indole-C3-alkylation with benzylamines is described, which can be combined sequentially with a new visible-light-driven catalytic photooxidation/1,2-shift reaction. The one-flask tandem process converts indoles into 3-benzylindole intermediates, which are further transformed into new fluorescent 2,2-disubstituted indoline-3-one derivatives.
A common synthetic route to indoxyl and 2‐oxindole alkaloids utilizes the oxidation of indoles to 3‐hydroxyindolenines, followed by acid‐mediated 1,2‐rearrangement. However, controlling the regioselectivity is often challenging and there is an ongoing need for new reaction conditions allowing to steer product selectivity. We report herein that phosphoric acids are ideal organocatalysts for the highly regioselective 1,2‐rearrangement of 3‐hydroxyindolenines to 2‐oxindoles, with predictable product selectivity arising from an efficient dual activation mode.
Quinone organocatalysis is an emerging area, and this report highlights some recently developed thermal and photocatalytic reactions, with particular emphasis on photooxygenation reactions. Further, it is discussed how the orthogonal ground-and excitedstate reactivities of quinones can be utilized for the development of tandem catalytic processes.
Wegen ihrer orthogonalen Reaktivitäten im Grundund angeregten Zustand sind Chinone interessante Organokatalysatoren für die Entwicklung sequenzieller katalytischer Verfahren. Die Entdeckung einer thermischen Chinon-katalysierten C3-Alkylierung von Indolen mit Benzylaminen wird beschrieben, die sequenziell mit einer neuen, durch sichtbares Licht induzierten Photooxidation/1,2-Umlagerung kombiniert wurde. Das Eintopf-Tandemverfahren setzt Indole zu 3-Benzylindolen um, die darauf zu neuen fluoreszierenden 2,2-disubstituierten Indolin-3-onen transformiert werden.
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