Cationic chiral surfactant based micelle-guided asymmetric Morita-Baylis-Hillman reaction

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.

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.

Micelle-guided Morita-Baylis-Hillman reaction of ketones in water

A novel Morita-Baylis-Hillman reaction employing electron-deficient alkenes like acrylonitrile with a wide range of aryl and aliphatic ketones using cooperative catalysis in micellar media has been delineated. This transformation executed in water under mild reaction conditions in a confined environment of micelles is aligned to the ideas of sustainable and green chemistry. The site of the reaction was established by incisive proton NMR studies in the palisade region of the micellar assembly. This study is expected to encourage the use of micellar catalysis for energetically less favorable chemical reactions.

Highly Efficient Asymmetric Morita–Baylis–Hillman Reaction Promoted by Chiral Aziridine-Phosphines

Continuing our research on the use of organophosphorus derivatives of aziridines in asymmetric synthesis and expanding the scope of their applicability, chiral aziridine-phosphines obtained earlier in our laboratory were used as chiral catalysts in the asymmetric Morita–Baylis–Hillman reaction of methyl vinyl ketone and methyl acrylate with various aromatic aldehydes. The desired chiral products were formed in moderate to high chemical yields and with enantiomeric excess reaching value of 98% ee in some cases. The use of catalysts being pairs of enantiomers led to the desired products with opposite absolute configurations.

Applications of Micelles in Catalyzing Organic Reactions

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Micellar chemistry is gaining considerable interest among organic chemists because these reactions are carried out in environmentally benign solvents like water. Owing to the exhaustive use of toxic solvents in carrying out the different chemical reactions, there is a pressing need for alternative approaches either environmental friendly or having minimum impact on the environment. In this article, we aim to discuss the various aspects of micellar chemistry viz-a-viz its role in guiding the chemical reactions. Micelles help to drive various kinds of organic reactions including oxidations, reductions, carbon-carbon bond formation, carbon-heteroatom bond formation, multi-component reactions, Pd-coupling reaction, olefin metathesis reaction, Morita-Baylis-Hillman reaction, etc. in water.

Recent designer surfactants for catalysis in water

Recent development of new designer surfactants further spurs the development of micellar catalysis in water for chemical transformations and catalysis, providing reliable alternatives to the employment of organic solvents.

Self-Assembly and Chiral Recognition of Chiral Cationic Gemini Surfactants

Chiral cationic gemini surfactants 1,4-bis(dodecyl- N, N-dimethylammonium bromide)-2,3-butanediol (12-4(OH)₂-12) including racemate, mesomer, and two enantiomers were synthesized and their self-assembly in aqueous solution has been comparatively investigated by tensiometry, conductometry, ¹H NMR, small-angle neutron scattering, cryogenic transmission electron microscopy, and cryogenic scanning electron microscopy. The chirality at spacer induces different self-assembly behaviors due to the hydrogen-bonding interaction between the hydroxyl groups at the chiral centers. The stereochemistry of the spacer has little effect on the release of the counterions from the surfactant headgroups and on the molecular packing at the air-water interface. The critical micelle concentration (CMC) decreases in the order of racemate > enantiomer > mesomer. Above the CMC, the aggregates of enantiomers transit from small spherical micelles to rodlike and wormlike micelles with increasing concentration, whereas the mesomer and racemate aggregates transform from spherical micelles to rodlike micelles and platelet-like aggregates. The differences may be because the mesomer and racemate molecules mainly form intermolecular hydrogen bonds between the -OH groups, but the enantiomer molecules dominantly form intramolecular hydrogen bonds. Furthermore, it was found that the chiral micelles formed by the enantiomers exhibit enantioselection ability for bilirubin (BR) enantiomers. The recognition capability can be adjusted by the micellar structure, i.e., the rodlike micelles are better than either small spherical micelles or wormlike micelles, which might possess different chiral cavities, controlling BR shape and location. These results demonstrate that the aggregates of chiral gemini surfactants can be used to mimic the chiral recognition in biological membrane.