Direct Experimental Evidence for the Priority of Flexible Ligand Skeleton in Asymmetric Friedel-Crafts Alkylation of Indole with Nitroalkenes

Direct experimental evidence for the priority of flexible ligand skeleton in asymmetric Friedel-Crafts alkylation was obtained through XRD analysis of flexible ligand/ZnCl2 complex, as well as synthesis of dihydroacridine-linked bis(oxazoline) ligands with planar rigid scaffold. A transition state model without NH … π interaction was proposed for the rigid ligands to interpret the inversion of absolute configuration. Keywords: Rigid scaffold, flexible scaffold, diphenylamine, dihydroacridine, bis(oxazoline), Friedel-Crafts alkylation