H-2- and C-13-labelling studies on skeletal reorganization of 1,6-enynes having a terminal alkyne moiety have been performed with various catalysts. The products are 1-vinylcyclopentenes, but two possible isomers, type I and II products, can be formed. The formation of type I involves the cleavage of the original C-C double bonds and migration of the terminal alkene carbon atom to the terminus of the alkyne. On the other hand. the formation of type II involves a double cleavage of the C-C double bond and the C-C triple bond, which is an anomalous bond connection. The product ratio is affected by the nature of the catalyst used. Type II is obtained as a major isomer in the case of late transition metal halides. On the other hand, the type I product forms exclusively in the presence of a typical element halide, such as InCl3.