One-Pot Cascade Reactions Catalyzed by Star Polymer Catalysts

star polymer catalysts - cascade reaction -

Significance

Non-interpenetrating two star polymer catalysts designed to mimic the site isolation characteristics of enzymes enabled a one-pot asymmetric cascade reaction. Thus, the one-pot nucleophilic addition of 2 to 1 and Michael addition of the resulting 3 to 4 were performed with a star polymer salt catalyst 6˙7 (20 mol%) [prepared from an acidic star polymer 6 and imidazolidinone (S,S)-7], a pyrrolidine star polymer (S)-8 (20 mol%), and a catechol mediator 9 (1 mol equiv) to give ( R,S )-5 in 89% yield with >99% ee and 96% de. The use of 10 or 11 in place of 6 or 8 under similar conditions did not give 5.

Comment

The acidic star polymer 6 was prepared from polystyrene macroinitiator 12, styrene 13, divinylbenzene 14 and phenyl p-styrenesulfonate 15 according to their previous report (Angew. Chem. Int. Ed. 2005, 44, 6384). The amine star polymer 8 was prepared via a similar procedure. Polystyrene macroinitiator 12 was developed by Hawker and co-workers (J. Am. Chem. Soc. 1999, 121, 3904). When imidazolidinone ( S,S )-7 was replaced with its enantiomer ( R,R )-7, a diastereomer ( S,S )-5 was obtained in 80% yield with >99% ee and 96% de.