PSRs Prepared by Polymerization

Supported borane amino alcohol complexes and other supported Lewis acids 

Preparation of the polymer [72] Suspension co-polymerization of styrene derivative 104 (1.41 g, 5 mmol), styrene 58 (4.16 g, 40 mmol), and cross-Hnking 

Cycloaddition [72] Methacrolein 106 (0.83 mL, 10 mmol) and cyclopenta-diene 107 (1.20 mL, 12 mmol) were added to the above-mentioned suspension of the catalyst at -78 °C. The mixture was stirred for 2 h at this temperature and then quenched with aqueous sodium hydrogencarbonate solution. Filtration, washing of the resin, and evaporation of the volatiles gave the product 108 (1.16 g, 85%). 

Other polymer-supported catalysts for the asymmetric Diels-Alder reaction include aluminum and titanium complexes of chiral amino alcohols [74], 

Polymer-supported chiral oxazoborolidines have also been used for the reduction of prochiral ketones. Enantiomeric excesses of 98% were obtained for the reduction of acetophenone using borane dimethyl sulfide as a stoichiometric reducing agent [77, 78]. 

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