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

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.