Cyclometalated Chiral-at-Ruthenium Catalyst for Enantioselective Ring-Closing C(sp3)–H Carbene Insertion to Access Chiral Flavanones

A cyclometalated ruthenium complex with exclusively metal-centered chirality catalyzes the conversion of diazoketones to chiral flavanones with up to 99% yield and with up to 96% ee. A competing oxygen attack pathway involving the formation and [1,2]-shift (Stevens rearrangement) of an oxonium ylide intermediate was successfully suppressed in favor of a catalytic enantioselective ring-closing C(sp3)–H carbene insertion. Density functional theory calculations provide a rationale for the observed C–H insertion over the undesirable C–O formation pathway. The method provides access to a variety of chiral flavanones which are considered privileged scaffolds with diverse biological activities.