Catalytic, asymmetric aza-Baylis-Hillman reaction of N-sulfonated imines with activated olefins by quinidine-derived chiral amines

The chiral nitrogen Lewis base, tricyclic cinchona alkaloid derivative TQO, is an effective promoter in the catalytic, asymmetric aza-Baylis-Hillman reaction of N-sulfonated imines Ar-CH=NR' 1 (R' = Ts, Ms, Ns, SES) with various activated olefins such as methyl vinyl ketone (MVK), ethyl vinyl ketone (EVK), acrolein, methyl acrylate, phenyl acrylate, or alpha-naphthyl acrylate to give the corresponding adducts in moderate to good yields with good to high ee (up to 99%) at -30 degrees C or 45 degrees C in various solvents, including DMF/MeCN (1:1, v/v). The first such reaction of 1 with the simplest Michael acceptor MVK and methyl acrylate has been achieved with excellent enantioselectivity. The adducts derived from MVK and EVK had the opposite absolute configuration to those from acrolein, methyl acrylate, phenyl acrylate, and alpha-naphthyl acrylate. A plausible mechanism has been proposed on the basis of previous reports and the authors' investigations. An effective bifunctional chiral nitrogen Lewis base-Bronsted acid system has been revealed in this type of aza-Baylis-Hillman reaction.