Annulation of pyridine as a route to quinolines, isoquinolines, and cycloheptapyridines
Pyridine-2,3- and -3,4-dicarboxylates have been condensed with dialkyl succinates and dialkyl glutarates to give diethyl 5,8-dihydroxyquinoline-6,7-dicarboxylate (7), diethyl 5,8-dihydroxyisoquinoline-6,7-dicarboxylate (24), and dialkyi 5,9-dihydroxy-7H-cyclohepta[b]- and -[c]pyridine-6,8-dicarboxylates (13), (14), and (26). The hydroxyquinoline and isoquinoline derivatives have been oxidised to the quinones (8) and (25); the former acts as a dienophile with cyclopentadiene. The dihydroxycycloheptapyridines have been converted into the cycloheptapyridine-5,9-diones (16) and (27) and into the cyclopropaquinolinediones (19) and (22), and the cyclopropaisoquinolinedione (29). Diels–Alder adducts (34) and (37) from pyrido[2,3-d]pyridazine-1,4-dione, and (35) from pyrido[3,4-d]pyridazine-1,4-dione have been prepared.