Aryne-Induced Novel Tandem 1,2-Addition/(3+2) Cycloaddition to Generate Imidazolidines and Pyrrolidines

A new “single‐flask” method was developed for the synthesis of imidazolidines and pyrrolidines with high stereoselectivity. First, a Schiff base was arylated with an aryne. Second, an intramolecular proton transfer took place from the methylene position to the anionic aryne ring. Third, the resultant ylide reacted with a second equivalent of the same Schiff base in situ or an electron‐deficient alkene through a (3+2) cycloaddition. These sequential tandem 1,2‐addition/(3+2) cycloaddition reactions led to the desired heterocycles in 63–88 % yields. Two steps in one flask: A sequence of arylation of a Schiff base, an intramolecular proton transfer from the methylene position to the anionic aryne ring, and reaction of the resulting ylide with either a second equivalent of Schiff base or an electron‐deficient alkene in a (3+2) cycloaddition generates imidazolidines and pyrrolidines in high stereoselectivity and 63–88 % yields.