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