We initially tried to use cyclopropyl-capped dienes (CPcapped dienes in short) and CO for the synthesis of eightmembered carbocycles, hypothesizing that the cyclopropyl (CP) group in the substrates can be cleaved, as many reactions of methylenecyclopropane (MCP) did. Instead, we found a [4+2+1] reaction of CP-capped diene-ynes/diene-enes with CO under the catalysis of rhodium, which is present in this paper (Scheme 1c). This unexpected and excited [4+2+1] reaction belongs to the SDS due to the following reasons. The CP group as the intermediate group in the CP-capped dienes is critical to the success of the [4+2+1] reaction, which helps the [4+2+1] through strain-release (see computational understanding part in this paper). On the other hand, the CP group can be further converted to other functional groups by applying cyclopropane