Helical polyisocyanide-based macroporous organic catalysts for asymmetric Michael addition with high efficiency and stereoselectivity

Abstract

Porous materials have attracted interest due to their high specific surface area and rich functionality. Immobilizing organocatalysts onto porous polymers not only boosts enantioselectivity but also improves the reaction rates. In this work, a series of porous polymers C-poly-3_ms with rigid polyisocyanide-carrying secondary amine pendants as building blocks were successfully prepared. And the pore size and optical activity of C-poly-3_ms can be controlled by the length of the polyisocyanide blocks due to their rigid and helical backbone. C-poly-3₁₅₀ demonstrated a preferred left-handed helix with a θ₃₆₄ value of −8.21 × 10³. The pore size and S_BET of C-poly-3₁₅₀ were 17.52 nm and 7.98 m² g⁻¹, respectively. The porous C-poly-3₁₅₀ catalyzes the asymmetric Michael addition reaction efficiently and generates the target products in satisfactory yield and excellent enantioselectivity. For 6ab, an enantiomeric excess (ee) and a diastereomeric ratio (dr) up to 99% and 99/1 could be achieved, respectively. The recovered catalyst can be recycled at least 6 times in the asymmetric Michael addition reaction while maintaining activity and stereoselectivity.