Asymmetric O-to-C Aryloxycarbonyl Migration of Indolyl Carbonates Using Single-Handed Dynamic Helical Polyquinoxalines Bearing 4-Aminopyridyl Groups as Chiral Nucleophilic Catalysts

Use of single-handed dynamic helical macromolecules as nucleophilic catalysts in asymmetric Steglich-type O-to-C aryloxycarbonyl rearrangement 3-substituted indol-2-yl aryl carbonates is demonstrated. Among several poly(quinoxaline-2,3-diyl) copolymers (PQXap) bearing achiral 4-aminopyridin-3-yl groups at the 5-position quinoxaline rings, PQXmdpp and PQXapy, containing N-methylpyrrolidine-fused pyridin-3-yl 4-(1-azetidinyl)pyridin-3-yl groups, respectively, showed higher enantioselectivity catalytic activity than PQXdmap, 4-dimethylaminopyridine-3-yl groups. Substrates p-(trifluoromethyl)phenyloxycarbonyl on both nitrogen oxygen atoms high reactivity, giving oxindoles with a quaternary stereogenic carbon center their 3-positions up to 97:3 enantiomeric ratio THF. The macromolecular underwent inversion helix sense by solvent effect, allowing same catalyst give opposite enantiomer mixture methyl t-butyl ether 1,1,2-trichloroethane (3:1). could be easily recovered adding acetonitrile reaction were reused four times without reduction enantioselectivity. Helically chiral derivatives 4-aminopyridine pendants served highly enantioselective carbonates, forming ratio. Solvent-dependent switching chirality well solubility enabled divergent enantioselection reuse.