The mechanism of an aerobic copper-catalyzed oxidative coupling reaction with N-phenyl tetrahydroisoquinoline was investigated. The oxidized species formed from the reaction of the amine with the copper catalyst were analyzed by NMR-spectroscopy. An iminium dichlorocuprate was found to be the reactive intermediate and could be structurally characterized by X-ray crystallography. The effect of methanol to effectively stabilize the iminium ion was investigated and shown to be beneficial in an oxidative allylation reaction.

Only oxygen and acid! The oxidative coupling of xanthene and other activated benzylic compounds with carbon nucleophiles such as ketones, can be performed under ambient conditions without solvent by simply using oxygen and catalytic amounts of methanesulfonic acid. The proposed reaction mechanism involves substrate activation by formation of hydroperoxides; the method can therefore be regarded as an “autoxidative coupling reaction”.

The combination of vanadium- and organocatalysis allows for the direct oxidative coupling of cyclic tertiary amines with non-activated ketones without the need for preformed leaving groups.

Waste not wasted: A mechanistic study of the autoxidative coupling of xanthene with cyclopentanone uncovered an autoinductive effect of the waste product hydrogen peroxide. It generates radicals in the presence of acid and ketones, which accelerate the reaction by providing an additional pathway to the reactive hydroperoxide intermediate. This discovery could be applied to achieve other Brønsted acid-catalyzed oxidative coupling reactions

The results from a kinetic investigation of a Cu-catalyzed oxidative coupling reaction between N-phenyl tetrahydroisoquinoline and a silyl enol ether using elemental oxygen as oxidant are presented. By using reaction progress kinetic analysis as an evaluation method for the obtained data, we discovered information regarding the reaction order of the substrates and catalysts. Based on this information and some additional experiments, a refined model for the initial oxidative activation of the amine substrate and the activation of the nucleophile by the catalyst was developed. The mechanistic information also helped to understand why silyl nucleophiles have previously failed in a related Cu-catalyzed reaction using tert-butyl hydroperoxide as oxidant and how to overcome this limitation.

Nur Sauerstoff und Säure! Die oxidative Kupplung von Xanthen und anderen aktivierten Benzylverbindungen mit Nukleophilen wie Ketonen benötigt lediglich Sauerstoff und katalytische Mengen an Methansulfonsäure. Lösungsmittel sind nicht erforderlich. Der vorgeschlagene Reaktionsmechanismus umfasst die Substrataktivierung durch Bildung eines Hydroperoxids. Daher kann diese Methode als „autoxidative Kupplungsreaktion“ angesehen werden.

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