Ionically polymer-immobilized MacMillan catalysts in continuous-flow asymmetric Diels–Alder reaction

Abstract Ionically polymer-immobilized chiral imidazolidinone (MacMillan) catalysts were synthesized through the radical polymerization of a cross-linked monomer, a comonomer, and a monomer with a chiral imidazolidinone moiety. The asymmetric Diels–Alder reaction of trans-cinnamaldehyde and 1,3-cyclopentadiene using the heterogeneous catalyst was performed by using a flow method. The catalyst P5a exhibited high reactivity (up to 84% yield) and high enantioselectivity (91% ee for the exo isomer and 96% ee for the endo isomer) in the continuous-flow system. Finally, when the asymmetric Diels–Alder reaction using P5b was performed for a longer period of time by using a continuous-flow method, even after 180 h, no catalyst leaching was observed, without loss of catalytic activity.