Brønsted Base-Catalyzed Reductive Cyclization of Alkynyl α-Iminoesters through Auto-Tandem Catalysis

A novel reductive cyclization of alkynyl α-iminoesters was developed through auto-tandem catalysis with a Brønsted base as the catalyst. The reaction system involves two mechanistically different elementary processes, both of which are efficiently catalyzed by an organosuperbase P2-tBu: the unprecedented reduction of α-iminoesters with 1-dodecanethiol as the reductant to provide α-aminoesters and the following intramolecular addition of ester enolates to an alkyne. The operationally simple reaction under mild conditions provides new efficient access to N-H indoline derivatives, demonstrating the high potential of auto-tandem catalysis with a Brønsted base as a methodology for organic synthesis.