Transition metal-catalyzed C-H activation/functionalization is a powerful strategy to realize atom- and step-economical organic synthesis of complex molecules. Among a wide range of metal catalysts studied, trivalent group 9 metal complexes bearing a pentamethylcyclopentadienyl ligand (Cp*CoIII, Cp*RhIII, and Cp*IrIII,) exhibit remarkable reactivity and functional group tolerance. Although catalytic stereocontrol in these catalyses has been achieved by the development of well-designed chiral cyclopentadienyl ligands, the difficulty in synthesizing such chiral Cp ligands may limit the derivatization for further application. Here we report that metal/organo hybrid systems efficiently control the enantioselectivity of C-H functionalization reactions without using chiral Cp ligands. Enantioselective C-H bond addition of 2-phenylpyridines or 6-arylpurines to enones proceeded in high enantioselectivities by Cp*RhIII/BINSate or Cp*RhIII/SPISate catalyst (Scheme 1a). We assume that reversible insertion of enones and enantioselective protonation by a chiral proton source generated in situ from the chiral disulfonate is a key to achieve the enantioselectivity. We also found that a chiral carboxylic acid can participate in a C-H activation step to achieve enantioselective C-H bond cleavage. C(sp2)-H alkylation/cyclization using dimethyl diazomalonate (Scheme 1b) and C(sp3)-H amidation using dioxazolones (Scheme 1c) proceeded in good to high enantioselectivity using a newly developed binaphthyl monocarboxylic acid and an amino acid derivative, respectively.

Metal/organo hybrid catalysis for group 9 metal-catalyzed enantioselective C-H functionalization

2019 Spring National Meeting

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