Catalytic deracemization of chiral allenes by sensitized excitation with visible light
Catalytic deracemization of chiral allenes by sensitized excitation with visible light
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DOI：
10.1038/s41586-018-0755-1
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发表时间：
2018-12-13
期刊：
影响因子：
64.8
通讯作者：
Bach, Thorsten
中科院分区：
文献类型：
--
作者：
Hoelzl-Hobmeier, Alena;Bauer, Andreas;Bach, Thorsten
手性化合物作为彼此不可重叠的镜像的对映体存在。由于对映体纯的手性化合物（1）的重要性-例如，作为活性药物成分-广泛地进行外消旋体（对映体的1：1混合物）的分离（2）。然而，通常只需要手性化合物的单一对映体形式，这就提出了如何将外消旋体选择性转化为单一对映体的问题。这种去外消旋化（3）过程在熵上是不利的，并且不能通过溶液中的常规催化剂进行。在这里，我们表明，它是可能的光化学deracemize手性化合物与高对映体选择性使用可见光（波长为420纳米）在催化量（2.5摩尔%）的手性敏化剂的存在下照射。我们将17个手性外消旋联烯转化为各自的单一对映体，对映体过量为89%至97%。敏化剂被假定为通过三重态能量转移到丙二烯来操作，对于两种对映体具有不同的能量转移效率。因此，它作为一种单向催化剂，转化一种对映异构体，但不转化另一种对映异构体，并且熵的减少由光能补偿。光化学去外消旋化使得能够从相同化合物的外消旋混合物直接形成对映体纯材料，从而为产生不对称性的挑战提供了新的方法。
Chiral compounds exist as enantiomers that are non-superimposable mirror images of each other. Owing to the importance of enantiomerically pure chiral compounds(1)-for example, as active pharmaceutical ingredients-separation of racemates (1:1 mixtures of enantiomers) is extensively performed(2). 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 deracemization(3) 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.