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.