Synthesis and structure of novel 1,2‐dihydro‐phthalazine containing betaines

1,2‐Dihydro‐2‐(4,5‐dihydroimidazol‐2yl)phthalazin‐1‐ol 1 reacts exothermically with dialkyl acetylenedicarboxylates to give 3‐[2‐(4,5‐dihydro‐1 H ‐imidazol‐3‐iurn‐2‐yl)‐1,2‐dihydro‐1‐phthalazin]‐1,4‐dialkoxy‐1,4‐dioxo‐2‐buten‐2‐olates 7 and 8 . Enolic ester compounds underwent further transesterification reactions with formation of the betaines 9 and 10 . The unequivocal structural assignement of these compounds was achieved by spectroscopic 1 H and 13 C nmr methods as well as X‐ray analysis of 7 .