## 2 Carbon-Carbon Forming Reactions
### Nitroaldolization Reaction  
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-aminophen  
Figure 6: Addition of terminal alkynes to imines catalysed by catalysts **2** and **11**.  
copper complexes as solid supported catalysts for the Henry reaction. The selected complex of copper(II) acetate, based on (_S,S_)-diphenylethylenediamine-derived imidazoline, (S)-phenylethylamine, and dibromophenol, was highly efficient and provided the products of the reaction (nitromethane with substituted aldehydes) in high yields (76-99%) and high enantioselectivity (75-95% ee). 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 um) [36]. Covalent anchoring of the ligand was performed by radical thiol-alkene click reaction, initiated thermally (azobisobutyronitrile (AIBN), toluene, reflux 24 h), as well as photochemically (2,2-dimethoxy-2-phenylacetophenone, \(\lambda_{\text{max}}=365\) nm, 40 W, DCM, 25 \({}^{\circ}\)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 corresponding substituted (R)-2-nitroethanols were produced in high yields (65-99%) and with high enantioselectivity (up to 92% ee) comparable with the homogeneous catalyst **13** (up to 96% ee). 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].  
The third variant represented heterogeneous catalysts **14a,b** based on Cu(II) complexes of substituted imidazolidine-4-thiones immobilized by means of sulfur atoms on different types of polystyrene carriers (polystyrene-co-4-vinylbenzyl chloride-_co_-tetra(ethylene glycol)-bis(4-vinylbenzyl) ether), Merrifield resin(tm) and Jandalel resin(tm) (Scheme 8) [38]. It was found, that catalysts **14a,b** catalyse the Henry reaction with high yields and high enantioselectivity, regardless of the polymeric carrier used (up to 98% ee). The obtained yields and enantioselectivity were comparable with the individual cases of reactions catalysed by analogical homogeneous catalysts **15a,b** (Scheme 8). Beside monitoring the yields and enantioselectivity, the possibility of recovery and reusing of catalysts **14a,b** was also studied. For instance, in the reaction of 2-methoxybenzaldehyde with nitromethane, the catalyst was reused more than 10 times without any decrease in enantioselectivity (81% ee) (Scheme 8) [38].