Recyclable catalyst for the asymmetric Henry reaction based on functionalized imidazolidine-4-one-copper(II) complexes supported by a polystyrene copolymer

Recent Advances in C–C and C–N Bond Forming Reactions Catalysed by Polystyrene-Supported Copper Complexes

“…The nitroaldolization (Henry) reaction catalysed by chiral optically pure catalysts is important among reactions; it involves the formation of a new carbon–carbon bond [ 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ]. This reaction occurs in the synthesis of substituted 2-nitroalcohols used e.g., for the preparation of biologically active compounds and medicinal drugs [ 34 ].…”

“…A recently published comprehensive paper [ 35 ] covers works concerning catalysts based on supported transition metal complexes aimed for an asymmetric variant of the Henry reaction. Three recent works were not covered in the above mentioned review [ 36 , 38 , 39 ]. The first work [ 39 ] included a study of a library of substituted polystyrylsulfonyl-imidazoline-aminophenol copper complexes as solid supported catalysts for the Henry reaction.…”

“…The same ligand as a complex with copper(II) triflate was examined in the Friedel–Crafts alkylation of indole by substituted nitroalkenes, to give the adducts in high yields (86–99%) and high enantioselectivity—up to 83% ee [ 39 ]. The second variant of immobilization represented recyclable the heterogeneous catalyst 12 ( Scheme 7 ), containing imidazolidine-4-one covalently bound on swellable pearl-like polystyrene having an –SH group (200–800 µm) [ 36 ]. Covalent anchoring of the ligand was performed by radical thiol-alkene click reaction, initiated thermally (azobisisobutyronitrile (AIBN), toluene, reflux 24 h), as well as photochemically (2,2-dimethoxy-2-phenylacetophenone, λ max = 365 nm, 40 W, DCM, 25 °C, 24 h).…”

“…Covalent anchoring of the ligand was performed by radical thiol-alkene click reaction, initiated thermally (azobisisobutyronitrile (AIBN), toluene, reflux 24 h), as well as photochemically (2,2-dimethoxy-2-phenylacetophenone, λ max = 365 nm, 40 W, DCM, 25 °C, 24 h). For the subsequent reaction of the copolymer with copper(II) acetate, heterogeneous catalyst 12 was prepared, and was characterized by elemental microanalysis and Raman spectroscopy [ 36 ]. Henry reactions proceeded in the polymeric matrix of swellable catalyst 12 with a rate comparable with the use of catalyst 13 in homogeneous media [ 37 ].…”

“…The reuse of catalyst 12 was studied for the reaction of pivalaldehyde with nitromethane. After five-fold recovery and reuse of heterogeneous catalyst 12 , a decrease in yield of about 24% occurred; on the other hand, the decrease in enantioselectivity was negligible (3% ee) ( Scheme 7 ) [ 36 ].…”