Catalytic deracemization of chiral allenes by sensitized excitation with visible light

Alena Hölzl-Hobmeier, Andreas Bauer, Alexandre Vieira Silva, Stefan M. Huber, Christoph Bannwarth and Thorsten Bach ()
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Alena Hölzl-Hobmeier: Technische Universität München
Andreas Bauer: Technische Universität München
Alexandre Vieira Silva: Technische Universität München
Stefan M. Huber: Fakultät für Chemie und Biochemie, Ruhr-Universität Bochum
Christoph Bannwarth: Mulliken Center for Theoretical Chemistry, Institut für Physikalische und Theoretische Chemie, Universität Bonn
Thorsten Bach: Technische Universität München

Nature, 2018, vol. 564, issue 7735, 240-243

Abstract: Abstract Chiral compounds exist as enantiomers that are non-superimposable mirror images of each other. Owing to the importance of enantiomerically pure chiral compounds1—for example, as active pharmaceutical ingredients—separation of racemates (1:1 mixtures of enantiomers) is extensively performed2. Frequently, however, only a single enantiomeric form of a chiral compound is required, which raises the question of how a racemate can be selectively converted into a single enantiomer. Such a deracemization3 process is entropically disfavoured and cannot be performed by a conventional catalyst in solution. Here we show that it is possible to photochemically deracemize chiral compounds with high enantioselectivity using irradiation with visible light (wavelength of 420 nanometres) in the presence of catalytic quantities (2.5 mole per cent) of a chiral sensitizer. We converted an array of 17 chiral racemic allenes into the respective single enantiomers with 89 to 97 per cent enantiomeric excess. The sensitizer is postulated to operate by triplet energy transfer to the allene, with different energy-transfer efficiencies for the two enantiomers. It thus serves as a unidirectional catalyst that converts one enantiomer but not the other, and the decrease in entropy is compensated by light energy. Photochemical deracemization enables the direct formation of enantiopure materials from a racemic mixture of the same compound, providing a novel approach to the challenge of creating asymmetry.

Keywords: Triplet Energy Transfer; Single Enantiomeric Form; Cent Enantiomeric Excess; Enantiopure Materials; Deracemization Process (search for similar items in EconPapers)
Date: 2018
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DOI: 10.1038/s41586-018-0755-1

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