The Asymmetric Friedel-Crafts Alkylation Of Indoles With α-Ketiminoesters Catalyzed By NCN Pincer Rhodium Complexes

This dissertation is mainly focused on the synthesis and characterization of a series of chiral NCN pincer rhodium(III) complexes with bis(imidazolinyl)phenyl ligands, some of the NCN pincer rhodium(III) complexes have been applied to catalyze asymmetric Friedel-Crafts alkylation of a-ketiminoesters and indoles.1. Synthesis and characterization of chiral NCN pincer rhodium(III) complexes with bis(imidazolinyl)phenyl ligandsChiral bis(imidazolinyl)phenyl ligands la-g were synthesized in a three-step sequence from commercially available isophthaloyl dichloride or 4,6-dimethylisophthaloyl dichloride and chiral amino alcohols. Ligands lh-j were synthesized in a two-step sequence from isophthalaldehyde and chiral diamine. Then the reaction of ligands 1 and triply hydrated rhodium trichloride afforded the corresponding chiral NCN pincer rhodium(Ⅲ) chloride complexes [(Phebim)RhCl2(H2O)] 2 via aryl C-H bond activation of the related ligands. The rhodium chloride complexes 2 were readily converted to the corresponding rhodium acetate complexes [(Phebim)Rh(OAc)2(H2O)] 3 by reaction with an excess of silver acetate (Scheme 1). New compounds 1e-j,2e-j,3e-f and 3h-j were fully characterized by elemental analysis (HR-MS for the new ligands le-j), 1H NMR,13C NMR. 2. The asymmetric Friedel-Crafts alkylation of α-ketiminoesters and indolesWe have explored the catalytic performance of the pincer rhodium(Ⅲ) catalysts in the asymmetric Friedel-Crafts alkylation of α-ketiminoesters and indoles. Results indicate that complex 3a displayed the efficient enantioselectivity, under the condition of 5 mol% catalyst loading, provide the corresponding chiral α-trifluorom ethyl-substituted α-amino acid derivatives 4 in 94% yield with enantioselectivities of up to 92% ee (Scheme 2).