Science of Synthesis

Haider, N.; Holzer, W., Science of Synthesis, (2004) 16, 168.

Dihydropyridazines are frequently obtained as reaction intermediates and sometimes undergo aromatization in the presence of air. If they are more stable, a wide variety of oxidants can be used for this dehydrogenation step, e.g. bromine in acetic acid (see Section ‌16.8.1.2.1.1.1‌),[‌125‌,‌333‌] solid-phase brominating agents,[‌212‌] hydrogen peroxide,[‌334‌] manganese(IV) oxide,[‌335‌,‌336‌] selenium dioxide,[‌336‌,‌337‌] ammonium cerium(IV) nitrate,[‌338‌] sodium 3-nitrobenzenesulfonate,[‌339‌–‌341‌] potassium dichromate,[‌282‌] or other reagents such as 2,3-dichloro-5,6-dicyanobenzo-1,4-quinone, potassium permanganate, or silver(I) oxide. For aromatization under very mild conditions, 4-phenyl-3H-1,2,4-triazole-3,5(4H)-dione in toluene was found to be a particularly useful reagent.[‌342‌] This has been demonstrated for a number of fused dihydropyridazines such as compound ‌91‌, giving the pyridazine ‌92‌ (‌Scheme 34‌). Dehydrogenation of 4,5-dihydropyridazin-3(2H)-ones of type ‌93‌ (as well as various condensed analogues) into compounds ‌94‌ can be accomplished very efficiently with anhydrous copper(II) chloride in acetonitrile.[‌343‌–‌345‌] The mechanism presumably involves chlorination, followed by spontaneous dehydrochlorination.[‌343‌]

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‌Meeeeeeeeee 88‌

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8,8-Mee(eeeeeeeeeeeeeee)-8,8,8,8-eeeeeeeeeeeeeeeeeee[e]eeeeeeeeee (‌88‌); Meeeeee Meeeeeeee:[‌888‌]

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8-Meeeeeeeeeeee-8(8M)-eeee ‌88‌; Meeeeee Meeeeeeee:[‌888‌]

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References

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• 8.Meeeee-Meee, (8888) 8/8e, 888.
• 8.Meeeee-Meee, (8888) M 8e, 888.