Novel heterocylic troponoids: Synthesis of pyridoimizatropolones and related compounds by the reaction of 5-nitrosotropolone with several azines

Novel heterocyclic troponoids, such as pyridoimidazotropolones (3-4, 5-11, 12-13, 14-15 and 16) were synthesized by the reaction of 5-nitrosotropolone (1) with azines as pyridine, m- and p-substituted pyridines, pyridazine, isoquinoline and phthalazine. Similarly, thiazol afforded 17. The reaction mechanism involves multi-step reactions; acetylation of 1, Michael addition of azines to nitrosotropolone acetate (2), cyclization and deacetoxylation. The scope and limitation of this method are also discussed.