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Chiral Lewis acids integrated with single-walled carbon nanotubes for asymmetric catalysis in water

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Science  19 Oct 2018:
Vol. 362, Issue 6412, pp. 311-315
DOI: 10.1126/science.aap7883

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Carbon nanotubes help nickel work in water

Most synthetic chemistry takes place in hydrocarbon-derived solvents. By contrast, enzymes manage to perform exquisitely selective reactions in water, often by surrounding reactants with hydrophobic pockets. Kitanosono et al. show that single-walled carbon nanotubes can similarly render simple nickel catalysts effective in water. Integration of the nickel ions with chiral ligands and surfactants at the nanotube surface produces a highly enantioselective catalyst for nitrone formation from aldoximes and unsaturated ketones. Spectroscopy suggests that the nanotubes enhance electron density at the nickel center as well as provide a hydrophobic milieu.

Science, this issue p. 311

Abstract

The development of highly reactive and stereoselective catalytic systems is required not only to improve existing synthetic methods but also to invent distinct chemical reactions. Herein, a homogenized combination of nickel-based Lewis acid–surfactant-combined catalysts and single-walled carbon nanotubes is shown to exhibit substantial activity in water. In addition to the enhanced reactivity, stereoselective performance and long-term stability were demonstrated in asymmetric conjugate addition reactions of aldoximes to furnish chiral nitrones in high yields with excellent selectivities. The practical and straightforward application of the designed catalysts in water provides an expedient, environmentally benign, and highly efficient pathway to access optically active compounds.

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