Solid Acids as Heterogeneous Support for Primary Amino Acid-Derived Diamines in Direct Asymmetric Aldol Reactions

We have achieved the non-covalent immobilization of chiral primary amino acid-derived diamines on organic and inorganic sulfonated solid acids through acid-base interaction. With the commercial sulfonated fluoropolymer nafion (R) NR50 as support an optimal balance was found between activity and stereoselectivity of the supported catalyst in direct asymmetric aldol reactions of linear ketones and aromatic aldehydes. Under optimized conditions aldol products were obtained in high yields and with excellent enantioselectivities for the syn-product (up to 98% ee). Furthermore, catalysis with the supported diamine was demonstrated to occur truly heterogeneously and the loaded nafion (R) NR50 beads could be reused several times. Ultimately, the immobilized catalyst/nafion (R) NR50 system was successfully implemented in a fixed-bed reactor set-up under continuous flow conditions.