# Advances in Organic and Organic-Inorganic Hybrid Polymeric Supports for Catalytic Applications
## 3 Organocatalyst Asymmetric Reactions
The activity and enantioselectivity of the catalysts were dependent on the length of the tether connecting the urea or thiourea functionality with the polymer. The catalysts **62e-f**, derived from 1,6-hexane diamine, showed the best performances, in 5 mol % loading without solvent and at room temperature. Under these conditions, the catalyst **62e** and **62f** were tested in the reaction of nitromethane with different \(N\)-Boc adlimines. A general trend showed that the catalyst **62f** was better than **62e**, giving products in higher yields and enantioselectivity except for two imines with substituents with strong electron withdrawing effect and an imine derived from 1-naphtaldehyde. Catalysts **62e** and **62f** were recycled for three and five times, respectively, without loss of enantioselectivity and with slight decrease in the activity. Recently, two sets of supported chiral thioureas, denoted as **67a-b** and **67c-d**, which differed in the length of the tether connecting the thiourea group to the polymer chain and in the effective functionalization, were prepared by copolymerization of styrene, divinylbenzene and novel styrylthiourea **66a** or **66b** respectively (Scheme 26) [50]. Styrylthioureas **66a** and **66b** were synthesized starting from commercially available \(N\),\(N^{\prime}\)-dimethylethylenediamine and \(N\),\(N^{\prime}\)-dimethyl-l,6-hexanedamine, respectively, by a common synthetic strategy which consisted in the following steps: (a) monoalkylation of previous diamines with 4-vinylbenzyl chloride to afford **63a** and **63b**; (b) reaction between Boc-L-valine and **63a** or **63b**; (c) reduction of the amide groups of **64a** and **64b** with LiAlH4; (d) removal of Boc protecting group by treatment with TFA; (e) reaction between 3,5-(bis)trifluoromethylisothiocyanate and triamine **65a** or **65b**. The catalytic activity of supported chiral thioureas **67a-d** was tested in aza-Henry reactions between of \(N\)-Boc-benzaldimine and nitromethane without solvent. The catalyst **67c** was used to extend the aza-Henry reaction between different aromatic \(N\)-Boc-aldimines and nitroalkanes. In the presence of catalyst **67c**, moderate to good enantioselectivities (ee: 72%-88%) and yields (51%-84%) were obtained in reactions with nitromethane. The two \(\alpha\)-nitroamines with two contiguous stereocenters, synthesized starting from nitroethane and nitropropane, were obtained with high yields (75%-84%) and enantioselectivities (ee: 88% for both examples), but with only moderate diastereoselectivity in case of the reaction with nitroethane (76:24). The catalyst **67c** was also employed in stereoselectivenitro-Michael addition between various nitroolefins and nucleophiles with different cyclic structures and activating groups. Moderate to high yields (79%-95%), diastereoselectivities (75:25-91:9) and enantioselectivities (74%-92%) were obtained. The recyclability was studied for both aza-Henry reaction and nitro-Michael addition. In both cases, the catalyst **67c** showed to be recyclable maintaining the level of stereocontrol and the catalytic activity. [PERSON] et al. reported the synthesis of the novel polystyrene-supported fluorinated organocatalyst **71** and its application in enantioselective Michael addition of aldehydes to nitroalkenes (Scheme 27) [51]. The supported organocatalyst **71** was prepared by co-polymerization of the chiral divinylated derivative **70** with styrene. The monomer **70** was synthesized by addition of 4-vinylphenyl magnesium bromide (prepared in situ) to the Boc-L proline methyl ester, followed by removal Boc group in basic media and deoxyfluorination of the obtained amino alcohol **69** by treatment with diethylaminosulfur trifluoride (DAST). **Scheme 27. Synthesis of the polystyrene-supported fluorinated organocatalyst **71** and its application in the enantioselective Michael addition of aldehydes to nitroalkenes. Effect of additives, reaction medium, loading of catalyst in addition of propanal to \(\beta\)-nitrostyrene were studied.