CINNOLINES AND PYRAZOLOPYRIDAZINES - NOVEL SYNTHETIC AND MECHANISTIC ASPECTS OF THE RICHTER REACTION

The thermal cyclization of 2-alkynylbenzenediazonium salts 2 known as the Richter reaction and leading, as described in the literature, only to 4-hydroxycinnolines 6 has been studied. A new probable route to th ese compounds involving intermediate formation of the 4-chlorocinnolin es 4 followed by hydrolysis of the latter to 6 is discussed. A new und erstanding of the reaction mechanism has induced us to change the reac tion conditions in order to synthesize some 4-bromo- (5), 4-chloro- (4 ), and 4-hydroxycinnolines 6 as well as 4-bromo- (8b) and 4-chloropyra zolopyridazine 8a.