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

Abstract

A supramolecule-based ruthenium catalyst has been developed for on-water aerobic oxidation of alcohols. The catalyst is synthesized by supporting ruthenium nanoparticles on cyclodextrinmodified graphene oxides (rGO@Ru-RMβ-CD) via a simultaneous onepot 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 −NH 2 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 O 2 and H 2 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.

Polydopamine: An Amine Oxidase Mimicking Sustainable Catalyst for the Synthesis of Nitrogen Heterocycles under Aqueous Conditions

“…Besides these, it also is a promising alternative to the conventional organic solvents, owing to which numerous research groups over the past decades have explored the prodigious potential of water as the reaction medium. , Thus, the development of water-compatible catalysts for the establishment of eco-friendly sustainable protocols are the need of the hour. Therefore, taking into account of the aforementioned advantages of metal-free protocols under aqueous conditions and the drawbacks of existing regime of catalysts, in continuation to our efforts to develop sustainable protocols using benign catalysts, − we herein report a biomimicking process wherein polydopamine is used as an organocatalyst for the oxidation of benzylic primary amines, alkyl amines and secondary amines aerobically. The formed intermediate imines are trapped by diamines (or) amides and aerobically oxidized to afford nitrogen heterocycles such as benzimidazoles, quinoxalines, and quinazolinones, as well as other heterocycles such as quinolines and indole via a domino/cascade process (Scheme ).…”

Synthetic Application of Cyclodextrins in Combination with Metal Ions, Complexes, and Metal Particles

“…Subsequently, they mixed reduced graphene oxide (rGO), raMeβCD, and RuCl 3 followed by reduction with NaBH 4 to produce a catalyst bearing Ru 0 particles (2.5 wt %, average diameter 4.7 nm; XPS 3p 3/2 461.2 eV, 3p 1/2 483.4 eV) [74] . The catalyst probed in the oxidation of alcohols showed similar features to those in Scheme 9 (yields of 60–93 %; 2 mol % Ru, O 2 balloon, K 2 CO 3 , H 2 O, 85 °C, 8–24 h).…”

Carbon‐Support‐Based Heterogeneous Nanocatalysts: Synthesis and Applications in Organic Reactions

“…Patil et al. developed a cyclodextrin based supramolecular catalyst (rGO@Ru‐RMβ‐CD) in which Ru nanoparticles are decorated over a cyclodextrin modified sheet of graphene oxide and utilized it for aerobic oxidation of alcohols (Figure ) . The authors also witnessed the good selectivity of supramolecular rGO@Ru‐RMβ‐CD catalyst for a broad range of substrates and sensitive functionalities.…”