Harnessing Chalcogen-bonding Interactions To Establish Conformational Control in Dirhodium(II) Paddlewheel Complexes

Novel well-defined D2-symmetric dirhodium(II) carboxylate complexes that bear axially chiral binaphthothiophene delta-amino acid derivatives have been developed. Conformational control was achieved through chalcogen-bonding interactions between sulfur and oxygen atoms in each ligand, providing well-defined and uniform asymmetric environments around the catalytically active Rh(II) centers. These structural properties render such complexes excellent catalysts for the inside-type asymmetric intramolecular C–H insertion into alpha-aryl-alpha-diazoacetates to yield a variety of cis- alpha, beta-diaryl gamma-lactones, as well as the corresponding trans-isomers through epimerization, in high diastereo- and enantioselectivities. Short total syntheses of the naturally occurring gamma-lactones cinnamomumolide, cinncassin A7, and cinnamomulactone were also accomplished using this conformationally controlled catalyst.