Micellar Catalysis as a Tool for C-H Bond Functionalization toward C-C Bond Formation

Micelle-mediated synthesis of quinoxaline, 1,4-benzoxazine and 1,4-benzothiazine scaffolds from styrenes

A range of heterocycles based on quinoxalines, 1,4-benzoxazines and 1,4-benzothiazines have been accessed from styrenes by reacting them with benzene-1,2-diamine, 2-aminophenol and 2-aminothiophenol respectively in micellar medium. This reaction occurring in a less explored cetylpyridinium bromide (CPB) micellar medium operates in the presence of NBS through a tandem hydrobromination-oxidation cascade, converting styrenes to phenacyl bromides. Its subsequent nucleophilic addition with aromatic 1,2-dinucleophiles and further transformations led to the formation of heterocyclic constructs. The locus of the reaction site was confirmed through NMR studies and the types of interactions between the CPB and solubilizates were established by DFT calculations.

The impact of earth-abundant metals as a replacement for Pd in cross coupling reactions

Substitution of one metal catalyst for another is not as straightforward as simply justifying this change based on the availability and/or cost of the metals. Methodologies to properly assess options for reaction design, including multiple factors like a metal's availability, cost, or environmental indicators have not advanced at the pace needed, leaving decisions to be made along these lines more challenging. Isolated indicators can lead to conclusions being made in too hasty a fashion. Therefore, an extensive life cycle-like assessment was performed documenting that the commonly held view that methods using earth-abundant metals (and in this case study, Ni) are inherently green replacements for methods using palladium in cross-coupling reactions, and Suzuki-Miyaura couplings, in particular, is an incomplete analysis of the entire picture. This notion can be misleading, and unfortunately derives mainly from the standpoint of price, and to some degree, relative natural abundance associated with the impact of mining of each metal. A more accurate picture emerges when several additional reaction parameters involved in the compared couplings are considered. The analysis points to the major impact that use of organic solvents has in these couplings, while the metals themselves actually play subordinate roles in terms of CO2-release into the environment and hence, the overall carbon footprint (i.e., climate change). The conclusion is that a far more detailed analysis is required than that typically being utilized.

Discovery and application of food catalysts to promote the coupling of PQQ (quinone) with amines

Background

Biocatalysts (enzymes) play a crucial role in catalyzing specific reactions across various industries, often offering environmentally friendly and sustainable alternatives to chemical catalysts. However, their catalytic activities are susceptible to denaturation. In this study, we present the discovery of novel protein-based biocatalysts derived from processed foods, including skimmed milk, soy milk, cheese, and dried tofu. These food catalysts exhibit high availability, low cost, safety, and thermo-stability.

Results

Focusing on the physiologically intriguing coenzyme pyrroloquinoline quinone (PQQ), we observed that the reaction with glycine to form imidazolopyrroquinoline (IPQ) did not proceed efficiently when PQQ was present at very low concentrations. Surprisingly, in the presence of protein-based foods, this reaction was significantly accelerated. Notably, skimmed milk enhanced the PQQ detection limit (600 times lower) during high-performance liquid chromatography (HPLC) following IPQ derivatization. Milk appears to facilitate the reaction between PQQ and various amino acids, primary amines, and secondary amines. Further investigations revealed that food catalysis operates through a non-enzymatic mechanism. Additionally, nuclear magnetic resonance spectroscopy demonstrated that milk components interacted with amino substrates due to the ability of amines to react with quinones on colloidal surfaces.

Conclusion

These practical food catalysts not only contribute to environmental safety but also hold significance across diverse scientific domains. Non-enzymatic protein catalysts find applications in biocatalysis, organic synthesis, food technology, analytical chemistry, and fundamental nutritional and evolutionary studies.

Photochemical cyclopropanation in aqueous micellar media - experimental and theoretical studies

While in nature, reactions occur in water-based confined compartments, for a long time, water has been often regarded as an unsuitable medium for organic reactions. We have, however, found that photochemical cyclopropanation of styrenes with diazo compounds or their precursors can be performed in micellar systems. COSMO-RS studies revealed that the reactivity correlates with the predicted critical micelle concentration (CMC), with higher CMC values delivering higher yields.

Nanoparticles as Heterogeneous Catalysts for ppm Pd-Catalyzed Aminations in Water

A general protocol employing heterogeneous catalysis has been developed that enables ppm of Pd-catalyzed C-N cross-coupling reactions under aqueous micellar catalysis. A new nanoparticle catalyst containing specifically ligated Pd, in combination with nanoreactors composed of the designer surfactant Savie, a biodegradable amphiphile, catalyzes C-N bond formations in recyclable water. A variety of coupling partners, ranging from highly functionalized pharmaceutically relevant APIs to educts from the Merck Informer Library, readily participate under these environmentally responsible, sustainable reaction conditions. Other key features associated with this report include the low levels of residual Pd found in the products, the recyclability of the aqueous reaction medium, the use of ocean water as an alternative source of reaction medium, options for the use of pseudohalides as alternative reaction partners, and associated low E factors. In addition, an unprecedented 5-step, one-pot sequence is presented, featuring several of the most widely used transformations in the pharmaceutical industry, suggesting potential industrial applications.

A micelle-mediated approach enables facile access to bridged oxabicyclo[n.3.1]alkene scaffolds

Oxabicyclo[n.3.1]alkene scaffolds present in a diverse range of complex natural products have been accessed by reacting 2-cycloalkenones with 1,3-cycloalkadiones in a micellar medium. This reaction occurring in a micellar confinement environment operates through a Michael addition/enolization/oxygen addition cascade to furnish highly functionalized constructs using a sustainable organic synthesis protocol. NMR analysis confirms that the locus of the solubilizates is within the palisade and stern regions of the micellar cavity.