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

Ionically polymer-immobilized chiral imidazolidinone (MacMillan) catalysts were synthesized by the radical polymerization of a crosslinked 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 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 using a continuous flow method, even after 180 h, no catalyst leaching was observed, without loss of catalytic activity.