Direct catalytic asymmetric Mannich-type reactions of γ-butenolides:: Effectiveness of Bronsted acid in chiral metal catalysis

Direct catalytic asymmetric Mannich-type reactions of gamma-butenolides are described. A chiral Lewis acid/amine base/Bronsted acid combination was used to catalyze a gamma-addition of gamma-butenolides to N-diphenylphosphinoyl imines, affording the products in up to >99% yield, anti/syn = >97:3, and 84% ee. The use of a catalytic amount of TfOH in addition to La(OTf)(3)/Me-PyBox/TMEDA was important for improving yield and stereoselectivity.