TY - JOUR
T1 - Catalytic deracemization of chiral allenes by sensitized excitation with visible light
AU - Hölzl-Hobmeier, Alena
AU - Bauer, Andreas
AU - Silva, Alexandre Vieira
AU - Huber, Stefan M.
AU - Bannwarth, Christoph
AU - Bach, Thorsten
N1 - Publisher Copyright:
© 2018, Springer Nature Limited.
PY - 2018/12/13
Y1 - 2018/12/13
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=85058552111&partnerID=8YFLogxK
U2 - 10.1038/s41586-018-0755-1
DO - 10.1038/s41586-018-0755-1
M3 - Article
C2 - 30542163
AN - SCOPUS:85058552111
SN - 0028-0836
VL - 564
SP - 240
EP - 243
JO - Nature
JF - Nature
IS - 7735
ER -