Mechanism of the Diels-Alder reaction of paramagneticendohedral metallofullerene and 1,2,3,4,5-pentamethylcyclopentadiene has been studied. Three-step large-scale preparation of 1,2,3,4,5-pentamethylcyclopentadiene has been reported. Reaction of 1,2,3,4,5-pentamethylcyclopentadiene (HCp*) with actinide ions in gas phase has been investigated by laser ablation mass spectrometry. It undergoes radical cation catalyzed cycloaddition with electron rich allenes to form Diels-Alder product.