Organocatalytic C–C bond activation of cyclopropenones for ring-opening formal [3 + 2] cycloaddition with isatins

Cyclopropenones were first applied as potential 3C synthons in ring-opening formal cycloaddition via an organocatalytic C-C bond activation strategy. This [3 + 2] cycloaddition of cyclopropenones with isatins catalyzed by using two different Lewis bases offers rapid access to spirooxindoles 3 and 4 regioselectively. These findings will provide helpful guidelines for further investigation of the reactivity of cyclopropenones with organocatalysis.