Polymer supported enantioselective reactions. II. α-Methylation of cyclohexanone

Abstract

Insoluble cross-linked copolymers of styrene and 1% divinylbenzene with covalently bonded (S)-2-aminoalkoxy groups were used in the enantioselective α-methylation of cyclohexanone through the corresponding imines. Enantiomeric excesses of 94% of (S)-2-methylcyclohexanone were observed on methylation at 20 °C. An analogous optically active 2-aminoalkyl benzyl ether, under otherwise identical conditions, resulted in a lower enantiomeric excess (49%) with selectivity approaching that of the polymer only at −78 °C.