Brønsted Base‐Catalyzed Umpolung Intramolecular Cyclization of Alkynyl Imines

A novel “umpolung” intramolecular cyclization of alkynyl imines, in which the electrophilic imine sp 2 ‐carbon formally serves as a nucleophilic site, was developed under Brønsted base catalysis. The reaction involves the unprecedented catalytic generation of α‐aminoester enolates from α‐iminoesters via the 1,2‐addition of the anion of a secondary phosphite to an imine moiety followed by the [1,2]‐rearrangement of a dialkoxyphosphoryl moiety from carbon to nitrogen, which is a formal umpolung process, and the intramolecular addition to an alkyne. This is a rare example of a [1,2]‐rearrangement of a dialkoxyphosphoryl moiety from carbon to nitrogen to generate an α‐amino carbanion and the first catalytic carbon–carbon bond forming reaction utilizing the resulting carbanion as a nucleophile.