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

摘要

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 func- tional ionic liquids as catalysts was developed, affording a vari- ety of spiro[pyrrolidine-benzofuran-3-one] compounds contain- ing 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-benzo- furan-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.