Enantioselective Synthesis of Spirocyclic Oxindole-β-lactones via N-Heterocyclic Carbene-Catalyzed Cycloaddition of Ketenes and Isatins

Chiral N-heterocyclic carbenes were found to be efficient catalysts for the formal [2+2] cycloaddition reaction of disubstituted ketenes and isatins to give the corresponding spirocyclic oxindole-beta-lactones in good yields with good diastereoselectivities and excellent enantioselectivities Ring opening with Grignard reagents or decarboxylation of the oxindole spirocyclic-beta-lactone gave the corresponding 3-hydroxy- or 3-alkylenyloxindoles in good yields