Solid supported 9-amino-9-deoxy-epi-quinine as efficient organocatalyst for stereoselective reactions in batch and under continuous flow conditions

Polystyrene-supported 9-amino-9-deoxy-epi-quinine was synthesized through co-polymerization of an ad hoc-designed chiral monomer with divinylbenzene, in the presence of azobis(isobutyronitile) (AIBN) as radical initiator and toluene and 1-dodecanol as porogenic solvents. The heterogenized catalyst efficiently promoted the reaction of isobutyric aldehyde with b-nitrostyrene, in very high yield and enantioselectivity, comparable or even higher than that of the homogeneous counterpart (up to 95% ee). The recyclability of the catalyst, its general applicability and its successful application to other reactions was also demonstrated. Finally, for the first time, a 9-amino- epi-quinine derivative was employed to perform an enantioselective Michael reaction under continuous-flow conditions; by using a home-made, packed-bed catalytic reactor, the aldehyde addition to nitrostyrene was successfully realized in flow mode, leading to the product in up to 93% ee.