Nickel-catalysed asymmetric hydrogenation of oximes

Chiral hydroxylamines are vital substances in bioscience and versatile subunits in the preparation of a variety of functional molecules. However, asymmetric and non-asymmetric synthetic approaches to these compounds are far from satisfactory. Although atom-economic metal-catalysed asymmetric hydrogenations have been studied for over 50 years, the asymmetric hydrogenation of oximes to the corresponding chiral hydroxylamines remains challenging because of the labile N–O bond and inert C=N bond. Here we report an environmentally friendly, earth-abundant, transition-metal nickel-catalysed asymmetric hydrogenation of oximes, affording the corresponding chiral hydroxylamines with up to 99% yield, 99% e.e. and with a substrate/catalyst ratio of 1,000. Computational results indicate that the weak interactions between the catalyst and substrate play crucial roles not only in the transition states, but also during the approach of the substrate to the catalyst, by selectively reducing the reaction barriers and thus improving the reaction efficiency and securing the generation of chirality. The asymmetric hydrogenation of oximes to chiral hydroxylamines is a long-standing challenge because of the labile N–O bond and inert C=N bond. Now, it has been shown that this reaction can be catalysed with a chiral nickel complex, and the weak interactions between catalyst and substrate are found to play a crucial role.