Palladium-catalyzed stereoselective decarboxylative [4 + 2] cyclization of 2-methylidenetrimethylene carbonates with pyrrolidone-derived enones: Straightforward access to chiral tetrahydropyran-fused spiro-pyrrolidine-2,3-diones

A novel asymmetric [4 + 2] cycloaddition of 2-methylidenetrimethylene carbonate with pyrrolidonederived enones has been achieved to produce the functionalized tetrahydropyran-fused spirocyclic scaffolds via palladium-catalysis. An array of enantioenriched spiro-pyrrolidine-2,3-diones bearing adjacent quaternary and tertiary stereocenters are obtained in high yields with excellent enantioselectivities（up to 96% yield and 99% ee）. The further transformation of the product has been accomplished for the construction of medical interesting β2,2-amino acids and β-lactams. Preliminary mechanistic research was well conducted.