Asymmetric reactions that transform racemic mixtures into enantio-enriched products are in high demand, but classical kinetic resolution produces enantiopure compounds in <50% yield even in an ideal case. Many deracemization processes have thus been developed including dynamic kinetic resolution and dynamic kinetic asymmetric transformation, which can provide enantio-enriched products even after complete conversion of the racemic starting materials. However, these dynamic processes require racemization or symmetrization of the substrates or intermediates. We demonstrate a direct chemical enantio-convergent transformation without a racemization or symmetrization process. Copper(I)-catalysed asymmetric allylic substitution of a racemic allylic ether afforded a single enantiomer of an α-chiral allylboronate with complete conversion and high enantioselectivity (up to 98% enantiomeric excess). One enantiomer of the substrate undergoes an anti-SN2′-type reaction whereas the other enantiomer reacts via a syn-SN2′ pathway. The products, which cannot be prepared by dynamic procedures, have been used to construct all-carbon quaternary stereocentres.
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This work was supported by a Grant-in-Aid for Scientific Research (B) (JSPS) and the PRESTO program (JST). We thank T. Inabe for his assistance in X-ray analysis. Nippon Chemical Industrial is acknowledged for a gift of (R,R)-QuinoxP*. We also acknowledge DAICEL chemical industries for their help on the optical resolution of some starting materials.
The authors declare no competing financial interests.
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Ito, H., Kunii, S. & Sawamura, M. Direct enantio-convergent transformation of racemic substrates without racemization or symmetrization. Nature Chem 2, 972–976 (2010). https://doi.org/10.1038/nchem.801
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