Gas-phase pyrolysis of 1-cyclohexenyldiazomethane (17) and (2-methyl-1-cyclohexenyl)diazomethane (36) leads to the generation of cyclohexenylmethylenes, 13 and 27, respectively, whose intramolecular rearrangement mechanisms can be inferred from the stable end products. These substituted vinylmethylenes undergo intramolecular pi-addition, but apparently do not participate in an all-carbon Wolff rearrangement. The relevance of these results to the mechanism of the phenylcarbene rearrangement is discussed, and it is suggested that a pi-route with a bicycloheptatriene-like transition state may operate. An attempt to generate 1,3-cyclohexadienylmethylene is described.