Asymmetric Synthesis of Benzofuranones with a C3 Quaternary Center via an Addition/Cyclization Cascade Using Noncovalent N-Heterocyclic Carbene Catalysis

An asymmetric addition/cyclization cascade of amidoesters and iminoquinones is developed using noncovalent N-heterocyclic carbene (NHC) catalysis. The process enables access to various functionalized benzofuranones with an all-carbon quaternary stereocenter with high yields and ee values. The reaction displays a broad substrate scope. Via product modifications, enantioenriched synthesis of biologically relevant spirocyclic lactones and lactams is achieved. Substrate activation via noncovalent interaction with NHC is suggested for the process.