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.

Silicon-induced phenanthrene formation from benzynes and allenylsilanes.

Now directly feasible: The silicon atom in allenylsilanes enabled their reaction with two equivalents of benzynes to generate (α-phenanthrenyl)vinylsilanes in good to excellent yields through an unprecedented [2+2+2] pathway (see scheme).