Catalytic Asymmetric [4 + 1] Cyclization of Benzofuran-Derived Azadienes with 3-Chlorooxindoles.

A chiral guanidine-catalyzed asymmetric [4 + 1] cyclization of benzofuran-derived azadienes with 3-chlorooxindoles has been established, which constructed chiral spirooxindole frameworks with in situ generation of a five-membered ring with high diastereoselectivities (up to >95:5 dr) and good enantioselectivities (up to 94:6 er). This reaction represents the first catalytic asymmetric [4 + 1] cyclization of benzofuran-derived azadienes, which will enrich the research field of catalytic asymmetric cyclizations of such reactants. In addition, this reaction provides a useful strategy for the enantioselective construction of five-membered ring-based chiral spirooxindole scaffolds.