Diazocyclopentadiene (DCPD) was first prepared by Doering and DePuy in 1953.' Several years later, its photolysis in the saturated hydrocarbons, cyclo- pentane and cyclohexane, was shown to yield carbon- hydrogen insertion products ; these were attributed to the intermediacy of cyclopentadienylidene, I.2 Sub- sequently, DCPD was photolyzed in various matrices ... Repetition of the reported DCPD-cyclopentane photolysis afforded a liquid of literature boiling point, ...