2‐Chloro‐4,5‐dihydroimidazole, 8 . Syntheses of Novel Fused Heterocyclic Systems by Reactions of 1,2‐Dihydro‐2‐(4,5‐dihydroimidazol‐2‐yl)phthalazin‐1‐ol with Active Methylene Compounds

Three‐component reactions of 1 with pyridazine or phthalazine afforded the 1,2‐dihydro derivatives 2a and 2b , respectively. A similar reaction of 1 with phthalazine performed in aqueous NaOH led to the formation of pseudobase 3 . The latter compound proved to be an excellent substrate for the preparation of a series of novel 1,2‐dihydrophthalazine derivatives 4a–c, 5 as well as 6a–b by reactions with a variety of active methylene compounds.