We design and develop a general strategy for the assembly of multisubstituted 1,3-diene derivatives. This methodology proceeds through the cleavage of cyclopropenes via the rearrangement of the cyclopropyl radical to the allyl radical after the addition of a carbon-centered radical with a leaving group onto the strained double bond, leading to 1,3-diene products with the release of the leaving group. This approach represents a reaction mode for carbon-centered radical-mediated functionalization of cyclopropenes with ring cleavage. The transformation occurs under mild reaction conditions and shows high functional group tolerance. These highly valuable and modifiable 1,3-diene products show good antitumor activity against HCT116 cells.