Molecular oxygen-mediated functional group transformations in catalysis and beyond: Genesis of ortho-naphthoquinone catalysts

This Personal Account highlights the research contributions of the Kim and Oh groups in molecular oxygen-promoted reactions since 2016, focusing on aerobic oxidation and radical chemistry. The groups' early work involved copper catalysts, leading to the discovery of the aerobic oxidation of 2-naphthols to form ortho-naphthoquinones (o-NQ), which were later used as organocatalysts. Over time, research expanded from metal catalysis to organocatalysis and photochemistry, achieving breakthroughs in reaction pathways and radical chemistry under aerobic conditions. The Account first discusses metal-catalyzed aerobic oxidation reactions, including copper-catalyzed transformations of 2-naphthol derivatives, palladium-catalyzed hydroamination, and rhodium-catalyzed decarbonylative oxidation. Other reactions include copper-catalyzed oxidation of amines to nitrogen compounds, as well as the synthesis of isoquinolones and benzothiazoles. These methodologies highlight the broad applicability of molecular oxygen in metal catalysis, enabling efficient and selective transformations in organic synthesis. Next, the Account summarizes o-NQ-based aerobic oxidation protocols, including the dehydrogenation of amines to form (ket)imines and a deamination method converting amines into carbonyl compounds. The application of o-NQ catalysts led to the formation of indole-3-carboxylates and fused pyrimidin-4(3H)-ones, along with one-pot deaminative oxidation converting primary amines into carboxylic acids. The alcohol dehydrogenase-like activity of o-NQ catalysts was also used to oxidize alcohols to aldehydes and ketones. Additionally, a water-soluble redox-active amine oxidase-like catalyst, cacotheline, derived from a natural source, was identified. The catalytic versatility of o-NQ catalysts was demonstrated in the selective activation of amines and nitroalkanes for deaminative cross-coupling and N-nitrosation reactions, as well as novel catalytic methods for the hydrodeamination of aryl amines. The last section discusses visible-light-induced photochemistry of N-nitrosamines, generating aryl cations that underwent aromatic nucleophilic substitution. A redox-neutral selenofunctionalization method, regenerating diselenides from selenols using molecular oxygen without external catalysts, was also presented. The presented work highlights the development of novel and efficient catalytic reactions utilizing aerobic oxidation processes, enabling effective functional group transformations and the creation of diverse heterocyclic compounds.