Enantioselective Cu-catalyzed 1,4-addition of Me3Al to a 4,4-disubstituted cyclohexa-2,5-dienone: Novel effect of trialkylsilylOTf on enantioselectivity
The asymmetric Cu-catalyzed conjugate addition of Me3Al to cyclohexa-2,5-dienone in the presence of 20 mol% of chiral 2-aryloxazolines and 120 mol% of TBDMSOTf gave the corresponding addition product in good yield with enantiomeric purities of up to 68% ee under mild conditions. Without TBDMSOTf, the ee was dramatically decreased, even in the presence of chiral 2-aryloxazolines.