Chiral phosphine lewis bases catalyzed asymmetric aza-Baylis-Hiliman reaction of N-sulfonated imines with activated olefins

In the aza-Baylis-Hillman reaction of N-sulfonated imines (N-arylmethylidene-4-methylbenzenesulfonamides and others) with methyl vinyl ketone, ethyl vinyl ketone, and acrolein, we found that, in the presence of a catalytic amount of chiral phosphine Lewis base such as (R)-2'-diphenylphosphanyl[1, 1']binaphthalenyl-2-ol LB1 (10 mol %) and molecular sieve 4A, the corresponding aza-Baylis-Hillman adducts could be obtained in good yields with good to high ee (70-95% ee) at low temperature (similar to-30 to -20 degrees C) or at room temperature in THF, respectively. In CH2Cl2 upon heating at 40 degrees C, the aza-Baylis-Hillman reaction of N-sulfonated imines with phenyl acrylate or naphthyl acrylate gave the adducts in good to high yields (60-97%) with moderate ee (52-77%). The mechanistic insight has been investigated by P-31 and H-1 NMR spectroscopic measurements. The key enolate intermediate, which has been stabilized by intramolecular hydrogen bonding, has been observed by P-31 and H-1 NMR spectroscopy. An effective bifunctional Lewis base and Bronsted acid phosphine Lewis base system has been disclosed in this catalytic, asymmetric aza-Baylis-Hillman reaction.