Copper-Catalyzed Regioselective [4+2] Annulations between Diaryliodonium Salts and Alkynes: Design, Development, and Applications

Herein, a new reaction pattern of diaryliodonium salts was reported as novelty oxa-1,4-dipoles to undergo [4+2] cycloaddition reactions with alkynes. Broad spectrum of the two reaction partners could be utilized in this protocol, enabling an operationally simple, high yielding, and regioselective synthetic approach to isocoumarins. Particularly, good to excellent regioselectivities were achieved for the sterically unbiased unsymmetrical diaryl acetylenes, which was challenging for other transition metal-catalyzed processes. The reaction could be scaled up with the ideal 1:1 stoichiometry and the isocoumarin type natural products Oospolactone and Thunberginol A could be obtained in one or three steps through this methodology.