Unprecedented Concomitant Formation of Cu₂O–CD Nano-Superstructures During the Aerobic Oxidation of Alcohols and Their Catalytic Use in the Propargylamination Reaction: A Simultaneous Catalysis and Metal Waste Valorization (SCMWV) Method

Copper–cyclodextrins (CDs)-catalyzed aerobic oxidation of alcohols under aqueous conditions and a concomitant formation of Cu₂O–cyclodextrin nano-superstructures (Cu₂O–CD nps) during the reaction are reported. The use of affordable copper and cyclodextrin combination for aerobic oxidation precluding organic solvents makes it a benign methodology. Intriguingly, a diverse array of Cu₂O–CD nps with unique morphologies was obtained by varying copper salts, cyclodextrins, and bases. The nano-superstructures were characterized by different techniques, such as X-ray diffraction, X-ray photoelectron spectroscopy, differential scanning calorimetry-thermogravimetric analysis, scanning electron microscopy, time of flight secondary-ion mass spectrometry, and transmission electron microscopy to confer their authenticity. Interestingly, the nano-superstructures showed promising catalytic efficiency for a one-pot three-component propargylamination reaction. The used particles were found to be recoverable and recyclable for propargylamination for up to three cycles, with no loss of catalytic activity. Moreover, the concomitant formation of Cu₂O–CD nanostructures and their self-segregation during an aerobic oxidation reaction under homogenous conditions is a first-of-its-kind method depicting simultaneous catalysis and metal waste valorization (SCMWV). Overall, this new approach of reaping the benefits of homogenous metal catalysis and simultaneously sequestrating the metal into a high-value product might pave the way to develop many such SCMWV protocols in future

Recyclable Supramolecular Ruthenium Catalyst for the Selective Aerobic Oxidation of Alcohols on Water: Application to Total Synthesis of Brittonin A

A supramolecule-based ruthenium catalyst has been developed for on-water aerobic oxidation of alcohols. The catalyst is synthesized by supporting ruthenium nanoparticles on cyclodextrin-modified graphene oxides (rGO@Ru-RMβ-CD) via a simultaneous one-pot reduction of ruthenium precursor and graphite oxide in water. The rGO@Ru-RMβ-CD was completely characterized by various techniques such as X-ray diffraction, thermogravimetric analysis, Fourier transform infrared, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy to understand its morphology and structure. The catalyst showed promising efficiency with good selectivity for benzylic, propargylic, and aromatic alcohols under aqueous conditions. Sensitive functional groups such as −NH₂ and phenolic −OH were well tolerated under the reaction conditions and exclusively afforded the aldehydes in good to excellent yields with no side products. Moreover, the used catalyst was found to be easily recoverable and recyclable up to five times. Additionally, the developed oxidation methodology has been used as a key step for the total synthesis of natural product Brittonin A, including other functional group transformations such as Wittig olefination and reduction exclusively in water. Notably, these oxidation and reduction transformations could be carried out using the developed catalyst under aqueous conditions. This unique ability of the catalyst to switch between oxidation and reduction reactions simply by changing O₂ and H₂ atmospheres with a balloon assembly exemplifies its versatility. To the best of our knowledge this is a first report showing the total synthesis of a molecule completely on water