Immobilization of diphenylamine-linked bis(oxazoline) ligands and their application in the asymmetric friedel-crafts alkylation of indole derivatives with nitroalkenes

A diphenylamine-linked bis(oxazoline) ligand with trans-diphenyl substitution on the oxazoline rings has been immobilized onto one- to three-generation Fréchet-type dendrimers and a C₃-symmetric core structure. The catalytic activities and enantioselectivities of these new ligands were tested in the asymmetric Friedel-Crafts alkylation reactions of indole derivatives with, nitroalkenes. The two types of immobilized ligands exhibited similar enantioselectivities and substrate compatibilities to the free ligand trans-DPBO we reported previously. No dendrimer effect was observed in the kinetic investigation of the Fréchet-type dendrimer-immobilized ligands. The in situ recycling of the catalysts was also tested to illustrate the effect of reducing catalyst loading and the efficiency of our system.