Stereoselective Addition of Alkynes to Ketenimines: Copper/Amine Catalyzed Sulfonyl Azide-Alkyne Cycloaddition Reactions for the Synthesis of ()-1,3-Enynes.

Herein, we report a copper/amine catalyzed stereoselective addition of alkynes to ketenimine intermediates generated in situ from the sulfonyl azide-alkyne cycloaddition cascade for the stereoselective synthesis of ()-1,3-enynes. Significantly, for the first-time, enamine intermediates generated in the copper-catalyzed sulfonyl azide-alkyne cycloaddition reactions have been successfully trapped and isolated as the products. Density functional theory computations have also been performed and found to be consistent with the observed experimental stereoselectivity.