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Desymmetrization by Asymmetric Copper-Catalyzed Intramolecular C–H Insertion Reactions of α‑Diazo-β-oxosulfones

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journal contribution
posted on 04.03.2019 by Thomas A. Brouder, Catherine N. Slattery, Alan Ford, U. B. Rao Khandavilli, Eliška Skořepová, Kevin S. Eccles, Matteo Lusi, Simon E. Lawrence, Anita R. Maguire
Effective desymmetrization in copper-catalyzed intramolecular C–H insertion reactions of α-diazo-β-oxosulfones in the formation of fused thiopyran dioxides is described for the first time. The use of a copper–bis­(oxazoline)–NaBARF catalyst complex system leads to formation of the major thiopyran dioxide stereoisomer with up to 98:2 dr and up to 98% ee. The effect of varying the bis­(oxazoline) ligand, copper salt, and site of C–H insertion on both diastereo- and enantioselectivities of these intramolecular C–H insertion reactions has been investigated. Similarly, desymmetrization in the formation of a fused cyclopentanone proceeds with up to 64% ee. These results represent the highest enantioselectivity reported to date in a copper-mediated desymmetrization through C–H insertion.