Optically pure oxazolidines were synthesized in nearly quantitative yields from chiral hydroxyalkyl-functionalized imidazolinium salts. Acting as transient chiral diamino N-heterocyclic carbenes (NHCs), these oxazolidines allowed the efficient formation of well-defined copper(I) and gold(I) hydroxyalkyl-NHC complexes, which could be isolated, for the first time, as air stable complexes after silica gel chromatography. Interestingly, X-ray analysis of gold complexes revealed that the hydroxyl-function is not chelated to the metal. Computational studies suggested that both cyclisation to produce oxazolidine and O–H bond elimination to form the transient carbene (prior to coordination) occur through a concerted mechanism. The novel chiral copper-catalysts, as well as oxazolidines alone (copper free), demonstrated excellent performances in asymmetric conjugate addition and allylic alkylation with high regio- and enantio-selectivities (up to 99% ee).
Bibliographical noteKAUST Repository Item: Exported on 2022-09-14
Acknowledgements: We are grateful to the CNRS, the Ecole Nationale Supérieure de Chimie de Rennes. Umicore AG & Co is acknowledged for a generous gift of gold complexes. This work was supported by the Agence Nationale de la Recherche (ANR-16-CE07-0019 “Hel-NHC” grant to D. P.-B.). L. J. thanks Rennes Metropole for supporting this work through the AIS grant for young researchers. L. C., L. F. and Z. Z. thank the King Abdullah University of Science and Technology (KAUST) for supporting this work. For computer time, this research used the resources of the KAUST Super-computing Laboratory (KSL) at KAUST. We are grateful to Philippe Jéhan and the CRMPO core facility for HMRS of Au- and Cu-complexes.
ASJC Scopus subject areas
- General Chemistry