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.
Access optionsAccess options
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
The findings of this study are available within the paper and its Supplementary Information.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Financial support by the Deutsche Forschungsgemeinschaft (DFG) via grant Ba1372/20 and GRK 1626 (T.B.) and through the Cluster of Excellence (EXC 1069) RESOLV project (S.M.H.) is acknowledged. A.H.-H. thanks the research training group (Graduiertenkolleg GRK) 1626 ‘Chemical Photocatalysis’ for a scholarship. A.V.S. acknowledges the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for a post-doctoral research fellowship (BEX number 10744/13-4). C.B. is grateful to S. Grimme for discussions and for admission to computing clusters. We thank O. Ackermann and J. Kudermann for help with the high-performance liquid chromatography and gas–liquid chromatography analyses, A. Strauch for help with the circular dichroism measurements and A. Tröster for compounds for experimental comparison.
Nature thanks Y. Inoue and the other anonymous reviewer(s) for their contribution to the peer review of this work.