The catalytic activity of polydopamine (PDA) as an amine oxidase mimic is demonstrated under aqueous conditions for the synthesis of benzimidazoles, quinoxalines, quinazolinones and oxidation of secondary amines. The synthesis occurs through activation of the amines by the catechol-quinone moieties of PDA, followed by transamination and an oxidative cyclization of these benzylic (or) arylethyl imine adducts with o-phenylenediamines and 2-aminobenzamides akin to the amine oxidase enzymes in the presence of benign oxidant molecular oxygen. PDA demonstrated excellent efficiency on par with the existing regime of metal/nonmetal-based catalysts without any additives under aqueous conditions. The mechanistic studies showed evidence for an oxygen-mediated nonradical pathway via a quinone-imine step. Additionally, PDA was found to be easily recoverable and reusable for up to three cycles without any loss of catalytic activity. Moreover, the utility of nontoxic and cheap solvent such as water along with a biomimicking recyclable catalyst PDA makes it a benign protocol from the sustainability point of view.

Cu2O−cyclodextrin (Cu2O−CD) nanosuperstructures catalyzed oxidation of benzylic sp3 C−H bonds and secondary amines via C−H bond activation is demonstrated in this protocol. Cu2O−CD nanosuperstructures displayed excellent catalytic activity for the oxidative transformation of substrates in combination with a radical promoter N‐hydroxyphthalimide (NHPI) and molecular oxygen as the green oxidant to afford the corresponding oxidized products with high selectivity and excellent yields. Moreover, the nanosuperstructures were found to be stable during the reaction, easy to recover, and recyclable up to three cycles to afford the products consistently with no loss of catalytic activity. The remarkable feature of this protocol is that the catalyst Cu2O−CD remained intact even after three cycles without undergoing over‐oxidation or any phase changes. The phase purity of Cu2O was ascertained by various characterization techniques such as X‐ray diffraction (XRD), Scanning electron microscopy (SEM), High‐resolution transmission electron microscopy (HRTEM), X‐ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TGA), and Inductively coupled plasma atomic emission spectroscopy (ICP‐AES) analysis. Furthermore, to gain more detailed insights into the reaction mechanism, oxygen labelled catalyst i. e., Cu218O−CD nanosuperstructures were synthesized using H218O (18‐labelled water) to determine any possible dioxygen exchange mechanism operative by Cu218O oxide thereby ascribing the source of oxygen in the reaction. Several other control experiments such as Electron Spin Resonance (ESR) and radical quenching studies established the mechanism to traverse a radical pathway. Additionally, the developed Cu2O−CD catalyst was also showcased to efficiently mimic the activity of the enzyme (S)‐tetrahydroprotoberberine oxidase (STOX) for the biomimetic synthetic transformation of tetrahydropalmatine to palmatine hydroxide. Interestingly, the developed Cu2O−CD mediated benzylic oxidation was used as a key step for the first total synthesis of the natural product Swerilactone O, an unusual secoiridoid with unprecedented C13 skeleton wherein aldol condensation reaction followed by oxidation afforded the natural product in 69% yield for overall steps. The utility of benign, supramolecular, and recyclable catalyst Cu2O−CD for oxidative transformations under aerobic conditions endorses the sustainability of the developed protocol.