Base-promoted cyclization of propargyl amides.

We report a BuOK-promoted synthesis of 1,3-dihydro-2-pyrrol-2-one and 4-methylenepyrrolidin-2-one systems like intramolecular cyclization. The method features extremely short reaction times (5 min) and mild reaction conditions (rt), enabling the trapping of a propargyl unit by an amide enolate. An intriguing anionic chain mechanism is at work, which can trigger the isomerization of an -alkene giving access to the otherwise elusive -product.