Pyridazinium betaines

Photoisomerization of azomethinimines to diaziridines was observed in several classes of compound. Diazepine (271) was converted, even by sunlight, to its diaziridine isomer (68JA4738). Further photoisomerizations were observed with azomethinimines (272) obtained from pyrazolidones (70JPR161), and with some pyridazinium betaines (273). 

S-N rearrangement, 3, 36 ionization constants, 3, 4 oxidation, 3, 37 quatemization, 3, 17 Pyridazine-3 (2 H) - thiones analysis, 3, 2 tautomerism, 3, 5 Pyridazinium betaine, 3-oxido-photolysis, 3, 11 Pyridazinium betaine, 5-oxido-photolysis, 3, 11 Pyridazinium dicyanomethylide photolysis, 3, 12... 

The behavior of some related hydroxydiazine derivatives has also been examined. Whereas the pyridazinium betaine 207 is unreactive toward... 

Dieckmann condensation of the diester 523 gives compound 524 which is readily oxidized to the pyridazinium-5-olate 525 (R = COjEt). This betaine (525 R = COjEt) has been converted into a number of derivatives (525 R = H, CO2H, Br, NHPh, SCH2Ph). Photolysis of the betaines 525 (R = H, CO2Et) results in rearrangement to isomeric 4(3//)-pyrimi-dinones. Full details of another study of this type of photochemical rearrangement of pyridazinium-5-olates (142) have now been published. ... 

Pyridazinium-5-olate betaines are isomerized photochemically to corresponding pyrimidin-4-ones by a similar path (Scheme 12). 

Methylation (Mc2S04 or MeOTs) of pyridazin-3-ones (138) followed by deprotonation of the salts (139) gives good yields of the crystalline pyridazinium-3-olates(137 R = Me)(Vc=o 1550 cm ). These betaines (137 R = Me) appear to be unreactive toward dipolarophiles. ... 

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