MacMillan polymer-supported

A polymer-supported version of MacMillan s catalyst 114 has been developed by anchoring a tyrosine-derived imidazohdin-4 -one via a spacer to the monomethyl ether of PEG (Scheme 3.32) [62]. The reaction of N-benzyl-C-phenyl nitrone 115 with acrolein 116 proceeded in the presence of PEG-supported chiral imidazolidi-none and acid in wet nitromethane to give the isoxazolidine 117. The supported catalysts behaved very similarly to their nonsupported counterparts in terms of enantioselectivity, but were somewhat less efficient in terms of chemical yield. 

In 2008, Chi et al. reported a tandem reaction of indoles, a,P-unsaturated aldehydes, and methyl vinyl ketone (MVK) for the synthesis of chiral indole derivatives with two stereogenic centers [ 19]. To avoid the interference of the two secondary amine catalysts and cocatalyst acid, the soluble star polymer-based site isolatbn method was adopted, whereby the supported imidazolidinone catalyst promoted initial Friedel-Crafts alkylation and the supported pyrrolidine derivative promoted the following Michael addition to MVK (Scheme 9.19). Notably, simple combination of these catalysts in one pot didn t mediate the cascade reaction efficiently despite the fact that the MacMillan imidazolidinone and pyrrolidine catalyst can efficiently promote separate Friedel-Crafts reaction and Michael addition, respectively. Moreover, when the pyrrolidine catalyst was replaced by its enantiomer, a diaste-reomer of the product could be obtained with high enantioselectivity. This smdy presented a novel solution to the efficient combination of incompatible substrates and catalysts. 

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