Site- and enantiocontrol in intramolecular C-H insertion reactions of alpha-diazo carbonyl compounds catalyzed by dirhodium(II) carboxylates

The full potential of rhodium(II)-catalyzed intramolecular C-H insertion reactions of alpha-diazo carbonyl compounds as a powerful tool for the construction of both carbocycles and heterocycles has been developed by variation of the bridging ligands of the dirhodium(II) catalysts: (1) Dirhodium(II) tetrakis(triphenylacetate) featured by the steric bulk of the bridging ligands on the rhodium has been demonstrated to exhibit an exceptionally high order of selectivity for C-H insertion into methylene over methine on a cycloalkane ring as well as for aromatic substitution over aliphatic C-H insertion. (2) Dirhodium(II) complexes incorporating N-phthaloyl-(S)-amino acids as bridging ligands have proven to be the chiral catalysts of choice for allowing high levels of differentiation of enantiotopic methylene C-H bonds and enantiotopic benzene rings, affording optically active cyclopentanone, 2-azetidinone, and 2-indanone derivatives in up to 80%, 96%, and 98% ee, respectively.