The synthesis and chemical reactivity of pyridazinedione-based enediynes (1, 2) are described. Both of these enediynes, namely the dihydro compound 1 and its corresponding tetrahydro analogue 2, were prepared by double N, O-alkylation of the corresponding heterocyclic system with the acyclic enediynyl dibromide 8 in good yields. Their single- crystal X-ray structures revealed similar c, d distances (distance between the acetylenic ...