Highly stereoselective [4+2] cycloaddition of azlactones to β,γ-unsaturated α-ketoesters catalyzed by an axially chiral guanidine base

Sweet catalysis! The enantio-and diastereoselective cycloaddition reaction of azlactones with β,γ-unsaturated α-ketoesters was demonstrated by taking advantage of the multiple reactive sites on the azlactone with the use of an axially chiral guanidine-base catalyst. The most likely reaction pathway involves three consecutive steps to provide a facile access to α-amino δ-lactones with a sugar framework in a highly stereoselective manner (see scheme).