Synthesis of pyranopyrazoles with a chiral quaternary carbon stereocenter via copper-catalyzed enantioselective [3 + 3] cycloaddition.

A copper-catalyzed enantioselective [3 + 3] cycloaddition of propargyl carbonates and pyrazolones has been disclosed. This reaction provided an efficient route to synthesize pyranopyrazoles containing a chiral quaternary carbon stereocenter in good yields with good to excellent enantioselectivities. In addition, the hydroxyl group in the products could be conveniently transformed into a variety of functional groups, such as aldehyde, nitrile, alkene, ester and amide groups, which further increased the synthetic value of this reaction.