Chiral microspheres constructed by helical substituted polyacetylene: A new class of organocatalyst toward asymmetric catalysis

This article reports the first microspheres consisting of helical substituted polyacetylene and showing interesting asymmetric catalysis ability. For preparing such chiral microspheres, two acetylene-based monomers, M1L with l-proline pendant group and MA, underwent precipitation copolymerization in the presence of rhodium catalyst in a solvent mixture of butanone/n-heptane. Regular microspheres (approx. 1 μm in diameter) were successfully prepared under suitable conditions. According to CD and UV spectroscopy measurements, the microspheres exhibit considerable optical activity, resulting from the substituted polyacetylene chains adopting helical structures of preferred one-handed screw sense. The microspheres were used as a chiral organocatalyst to heterogeneously catalyze the asymmetric Aldol reaction of p-nitrobenzaldehyde and cyclohexanone in aqueous media. Remarkable catalytic efficiency was obtained (yield 76% and ee 80%). After catalysis, the microspheres can be easily recovered. The methodology created in this study provides opportunities for developing a new class of chiral polymer organocatalyst.