Synthesis of New Exocyclic Allenes with Diterpene Fragments

New stable allenes with exocyclic cumulene groups were synthesized from N-maleopimarimide-substituted amino acids using phenyl(triphenylphosphoranylidene)succinimide, 2-fluorophenyl(triphenylphosphoranylidene)-succinimide, and benzyl(triphenylphosphoranylidene)succinimide.