A Catalytic Method for the Preparation of Polysubstituted Cyclopentanes: [3+2] Cycloaddition of Vinylidenecyclopropanes with Activated Olefins Catalyzed by Triflic Imide

[3+2] Cycloadditions of vinylidenecyclopropanes (VDCPs) with electron-deficient olefins, such as methyl vinyl ketone (MVK) and acrylaldehyde, proceed smoothly in the presence of a catalytic amount of triflic imide (Tf2NH) to give the corresponding functionalized cyclopentanes in good to high yields.