Chiral oxazolidines acting as transient hydroxyalkyl-functionalized N-heterocyclic carbenes: an efficient route to air stable copper and gold complexes for asymmetric catalysis. Issue 30 (15th July 2022)

• Record Type: Journal Article
• Authors: Pichon-Barré, Delphine; Zhang, Ziyun; Cador, Aël; Vives, Thomas; Roisnel, Thierry; Baslé, Olivier; Jarrige, Lucie; Cavallo, Luigi; Falivene, Laura; Mauduit, Marc
• Is Part Of: Chemical science. Volume 13:Issue 30(2022)
• Page Start: 8773
• Page End: 8780
• Publication Date: 2022-07-15
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d2sc02908a
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : Well-defined chiral Cu(i ) and Au(i ) hydroxyalkyl NHC complexes were synthesized from oxazolidines. The copper-catalysts and oxazolidines alone (copper free), demonstrated excellent performances in asymmetric conjugate addition and allylic alkylation. Abstract : 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).