1,3‐Dipolar Cycloaddition of Benzofuranone Derivatives and Azomethine Ylides Promoted by Simple Functional Ionic Liquids: Direct Access to Highly Substituted Pyrrolidine and Spirocyclic Benzofuranone

We have successfully established an efficient catalytic system, which was effective for construction of both spiro[pyrrolidine‐benzofuran‐3‐one] and spiro[pyrrolidine‐benzofuran‐2‐one] compounds. The first 1,3‐dipolar cycloaddition of 2‐alkylidene‐benzofuran‐3‐one with azomethine ylides with simple functional ionic liquids as catalysts was developed, affording a variety of spiro[pyrrolidine‐benzofuran‐3‐one] compounds containing highly substituted pyrrolidine motifs with a spiro quaternary stereogenic center in excellent yields (73‐99 %). The highly efficient catalytic system exhibited broad substrate scopes under mild conditions. Meanwhile, this catalytic system was also extended to the cycloaddition of 3‐alkylidene‐benzofuran‐2‐one with azomethine ylides and gave spiro[pyrrolidine‐benzofuran‐2‐one] compounds in high yields (82‐99 %) and 1,3‐dipolar cycloaddition of 2‐alkylidene‐benzofuran‐3‐one with pyrazolidinone‐based dipoles giving the desired products in 25–85 % yields.