Excellent enantioselectivities of up to 98 % ee are achieved by employing the copper‐bis(oxazoline)‐NaBARF catalyst system in the C–H insertion reactions of α‐diazo‐β‐oxo sulfones. The influence of variation of the bis(oxazoline) ligand, copper salt, additive and substrate on both the efficiency and the enantioselectivities of these intramolecular C–H insertion reactions has been explored. Optimum enantioselectivities are achieved with phenyl and diphenyl ligands across the substrate series.

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Significant enhancements in enantioselectivities and reaction efficiencies in asymmetric copper-catalysed C-H insertion and aromatic addition reactions of a-diazocarbonyl compounds in the presence of various group I salts are reported. For the first time in carbenoid chemistry, evidence for the critical role of the metal cation is described.