Chiral oxazolidines acting as transient hydroxyalkyl-functionalized N-heterocyclic carbenes: an efficient route to air stable copper and gold complexes for asymmetric catalysis
Résumé
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).
Domaines
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Cite 10.5517/ccdc.csd.cc2854wh Jeu de données Pichon-Barré, Delphine, Zhang, Ziyun, Cador, Aël, Vives, Thomas, Roisnel, Thierry, Baslé, Olivier, Jarrige, Lucie, Cavallo, Luigi, Falivene, Laura, & Mauduit, Marc. (2022). CCDC 2090326: Experimental Crystal Structure Determination [Data set]. Cambridge Crystallographic Data Centre. https://doi.org/10.5517/CCDC.CSD.CC2854WH
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Cite 10.5517/ccdc.csd.cc2854vg Jeu de données Pichon-Barré, Delphine, Zhang, Ziyun, Cador, Aël, Vives, Thomas, Roisnel, Thierry, Baslé, Olivier, Jarrige, Lucie, Cavallo, Luigi, Falivene, Laura, & Mauduit, Marc. (2022). CCDC 2090325: Experimental Crystal Structure Determination [Data set]. Cambridge Crystallographic Data Centre. https://doi.org/10.5517/CCDC.CSD.CC2854VG
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Cite 10.5517/ccdc.csd.cc2854tf Jeu de données Pichon-Barré, Delphine, Zhang, Ziyun, Cador, Aël, Vives, Thomas, Roisnel, Thierry, Baslé, Olivier, Jarrige, Lucie, Cavallo, Luigi, Falivene, Laura, & Mauduit, Marc. (2022). CCDC 2090324: Experimental Crystal Structure Determination [Data set]. Cambridge Crystallographic Data Centre. https://doi.org/10.5517/CCDC.CSD.CC2854TF