Polymer-Supported Chiral Oxazaborolidinone

Significance

A chiral N-sulfonylated α-amino acid monomer carrying an (S)-tryptophan group was copolymerized with styrene and divinylbenzene to give a polymer-supported N-sulfonyl-(S)-tryptophan. Treatment of this polymer with 3,5-bis(trifluoromethyl)phenyl boron dichloride afforded a polymeric Lewis acid catalyst effective for the asymmetric Mukaiyama aldol reaction of silyl enol ethers and aldehydes. Various aldehydes were allowed to react with silyl enol ethers in the presence of the polymeric chiral Lewis acid to give the corresponding aldol adducts in good yields and enantioselectivities (47-99% yield, 70-95% ee).