Enantioselective Copper-Catalyzed [3 + 3] Cycloaddition of Tertiary Propargylic Esters with 1H-Pyrazol-5(4H)-ones toward Optically Active Spirooxindoles.

A copper-catalyzed enantioselective [3 + 3] cycloaddition of 3-ethynyl-2-oxoindolin-3-yl acetates with 1H-pyrazol-5(4H)-ones for the construction of optically active spirooxindoles bearing a spiro all-carbon quaternary stereocenter has been realized. With a combination of Cu(OTf)2 and chiral tridentate ketimine P,N,N-ligand as the catalyst, the reaction displayed broad substrate scopes, good yields, and high enantioselectivities. This represents the first catalytic asymmetric propargylic cycloaddition with tertiary propargylic esters as the bis-electrophiles for access to chiral spirocyclic frameworks.