Polymer assisted asymmetric reactions. II. Synthesis and application of a crosslinked resin containing (R)-1-(4-vinylphenyl)ethylamine

The preparation of crosslinked resins containing chiral 1-(p-vinylphenyl)ethylamine and its N-acetyl derivative is described. The optically active amine resin was used as a probe of the effect of polymer attachment of the chiral auxiliary on the enantioselectivity of an asymmetric alkylation reaction. α-Methylation of the cyclohexanone imine of the chiral resin at 0° affords, after hydrolysis, a much higher optical yield of (S)-2-methylcyclo-hexanone than can be obtained even at low temperature using 1-phenylethylamine as the chiral auxiliary. The increased enantioselectivity of the polymer-assisted reaction is likely due to a decrease in conformational mobility between the various alkylation pathways of the polymer-bound intermediate.