# Advances in Organic and Organic-Inorganic Hybrid Polymeric Supports for Catalytic Applications
## 3 Organocatalyst Asymmetric Reactions
The catalyst **71** (10 mol %) was employed in enantioselective Michael addition of a wide variety of aldehydes with \(\beta\)-nitrostyrene and in addition of propanal with different nitroalkenes under optimized conditions (10 mol % of catalyst, 10 mol % of 4-nitrophenol as additive, CH\({}_{2}\)Cl\({}_{2}\) as solvent and room temperature). Michael adducts were obtained with excellent yields and stereoselectivities. Furthermore, high stroselectivities and yields were obtained in reaction between isovaleraldehyde or isobutyraldehyde and different nitroalkenes, varying the type of additive or loading of catalyst and additive. Recycling experiments were carried out in reaction between propanal and \(\beta\)-nitrostyrene. The catalyst was recycled eight times. The stereoselectivity remained constant in all runs and some progressive loss of activity was observed in the last cycles. The catalyst **71** was also applied in a carefully designed continuous flow set-up, which allowed the facile isolation of the desired Michael adducts without chromatographic purification. The multigram synthesis of a single Michael adduct over a 13 h period and the sequential generation of a library of enantiopure Michael adducts from different combinations of substrates (16 examples, 16 runs, 18.5 h total operation) were observed. The immobilized system showed comparable activity with the batch process. Two polystyrene-supported imidazolidinone catalysts, **74** and **77**, were also prepared (Scheme 28) [52]. In catalyst **74**, the chiral imidazolidinone unit was linked to polystyrene through the \(N\)-3 atom. In catalyst **77**, the chiral imidazolidinone unit was linked to polystyrene through the 4-position of the phenyl ring. Polystyrene-supported imidazolidinone catalysts **74** and **77** were prepared starting from L-phenylalanine methyl ester and tyrosine methyl ester, respectively, by a procedure, which included the synthesis of an amide with ethanolamine in the first case or with butylamine in the second case, followed by reaction with acetone. Both imidazolidinones thus synthesized, **72** and **75**, were modified with 4-(chloromethyl)styrene and anchored to mercaptomethyl-modified polystyrene resin by the thiol-ene addition in presence of AlBN. The catalytic activity of two polystyrene-supported catalysts **74** and **77** was compared towards the asymmetric \(\alpha\)-alkylation of propanal with benzodithiolylium tetrafluoroborate in CH\({}_{3}\)CN as solvent and in presence of benzoic acid as additive. Catalyst **74** proved to be more active and enantioselective than **77**, affording the final products with yield of 97% and ee of 74% at the same levels of activity and enantioselectivity of the unsupported counterpart **73**. Catalyst **74** was highly recyclable for at least eight cycles with no loss of activity and enantioselectivity, whereas with catalyst **77** the yield and enantioselectivity decreased upon recycling. Chiral polyethers, containing imidazolidinone repeating units, were synthesized and employed as catalysts in asymmetric Diels-Alder reaction [53]. These polyethers, denoted as **81a-e(HX)**, were prepared following the synthetic route depicted in Scheme 29. At first, the bisphenol-type chiral imidazolidinone monomer **79** was afforded by reaction between the Boc-protected (S)-tyrosine and 4-hydroxyphenylethylamine, followed by deprotection of \(N\)-Boc group and reaction with acetone. Then, the Williamson synthesis of the chiral bisphenols **79** with dihalides afforded to polyethers **80a-e**, whose acid treatment led to the polyethers **81a-e(HX)**, having imidazolidinone salt in each repeating unit. Various types of dihalides (X-R-X) including allylic dihalide, alkyl dihalide, and benzylicdihalides and various types of acid, including HBF\({}_{4}\), CF\({}_{3}\)COOH, CH\({}_{3}\)SO\({}_{3}\)H, TolSO\({}_{3}\)H, HCl, HClO\({}_{4}\), were used to prepare these chiral polyethers.