Copper(I) catalyzed asymmetric oxidative cross-coupling copolymerization leading to alternating copolymers

The asymmetric oxidative coupling copolymerization of 6,6′-dihydroxy-2,2′-binaphthalene and dihexyl 6,6′-dihydroxy-2,2′-binaphthalene-7,7′-dicarboxylate with the copper(I)-diamine catalysts under an O₂ atmosphere was carried out. The copolymerization using the CuCl-(S)-(−)-2,2′-isopropylidenebis(4-phenyl-2-oxazoline) catalyst (S)Phbox], afforded a polymer with the high cross-coupling selectivity of 93%, that is, a copolymer with a mainly alternating structure, in 80% yield. The number-average molecular weight of the methanol-ethylacetate (1/3 v/v)-insoluble part of the copolymer was 1.1×10⁴. To estimate the enantioselectivity with respect to the cross-coupling linkage in the obtained copolymer, the model asymmetric oxidative cross-coupling reaction with CuCl-(S)Phbox was also examined, and the products showed a 96% cross-coupling selectivity and enantioselectivity of 43% ee (S).