A novel tandem 1,6-addition/cyclopropanation/rearrangement reaction of vinylogous para-quinone methides with 3-chlorooxindoles is reported. This method provides an efficient approach to various functionalized dispirooxindole–cyclopentane–cyclohexadienones with vicinal quaternary carbon centers. Computational studies have been conducted to provide insight into the origin of diastereoselectivity and predict a stepwise diradical mechanism. The anti-tumor activities of these structurally unique dispirooxindole derivatives are also reported.