Controlled Synthesis of One-Handed Helical Polymers Carrying Achiral Organoiodine Pendants for Enantioselective Synthesis of Quaternary All-Carbon Stereogenic Centers

摘要

Inspired by highly efficient and enantioselective reactions catalyzed by biomacromolecules, developing artificial helical polymer-based catalysts for enantioselective reactions is an interesting work. In this work, a series of one-handed helical polyisocyanides bearing aryl iodine pendants were readily produced via asymmetric polymerization of achiral isocyanides using chiral Pd(II)-catalysts. Despite the inexistence of any stereogenic centers, these polymers showed large optical activity owing to the one-handed helicity. Remarkably, these polymers could catalyze asymmetric dearomatization spirocyclization of 1-hydroxy-N-aryl-2-naphthamide derivatives and gave chiral spirooxindole products with high enantioselectivity. The enantioselectivity was contributed by the helicity of the polyisocyanide backbone; helical polyisocyanides in opposite helicity produced the enantiomeric antipode products with comparable yields and similar high enantioselectivity. Thanks to the high molecular weight, the helical polymer catalysts could be recycled 10 times with maintained activity and stereoselectivity.

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