Pyridazines from 1,4-dicarbonyl compounds

Dicarbonyl compounds pyridazine synthesis from, 3, 45 pyrrole synthesis from, 4, 329 reactions... 

Pyrazoles and pyridazines from hydrazine and dicarbonyl compounds... 

In planning the synthesis of a pyrrole or a pyridine from a dicarbonyl compound, considerable variation in oxidation state is possible Tire oxidation state is chosen to make further disconnection of the carbon skeleton as easy as possible. We can now see how these same principles can be applied to pyrazoles and pyridazines. 

Dihydropyridazines are obtained from 1,4-dicarbonyl compounds and hydrazine (Section III,B) or from the reaction of sym-tetrazines and simple ethylenic compounds (Section III,H). There are also a few special reactions, such as that between a tetrahydrofuran and phenylhydrazine, or from a 1,4,5,6-tetrahydropyridazine derivative. The 1,4-dihydro structure has been found to be correct, rather than the 1,6-dihydro structure, postulated earlier for some of these reduced pyridazines (Section III,H). 1,4-Dihydropyridazines can be reduced or oxidized easily and acid treatment of l-tosyl-1,4-dihydropyridazine causes rearrangement to 1-tosylaminopyrrole. ... 

Pyridazine syntheses from unsaturated 1,4-diketones have been applied in several new ways. ° The reaction with hydrazines is usually performed in the presence of mineral acid otherwise JV-aminopyrroles may be formed. Some saturated 1,4-diketones are claimed to react with hydrazines to give pyridazines. Instead of 1,4-dicarbonyl compounds,... 

Some lactones serve as starting material. y-Phenylazo-y-valerolactone is thermally rearranged to a mixture of pyridazinones 20 and 21 in a ratio of 1.75 1. A complex mechanism is proposed. Pyridazines also result from hydrazines and substituted y-lactones - or -acyl-y-lactones, which react as 1,4-dicarbonyl compounds. y-Chloroketones react with substituted hydrazines to gives pyridazines or Af-aminopyrrolines, depending upon the hydrazine used. ° y-Chlorobutanal gives the corresponding 1,4,5,6-tetrahydropyridazine. ... 

Each of the diazines can be constructed from an appropriate source of two nitrogens and a dicarbonyl compound. In the case of pyridazines, the nitrogen source is, of course, hydrazine and this in combination with 1,4-dicarbonyl compounds readily produces dihydro-pyridazines, which are very easily dehydrogenated to the aromatic heterocycle. Pyrimidines result from the interaction of a 1,3-dicarbonyl component and an amidine (as shown) or a urea (giving 2-pyrimidones) or a guanidine (giving 2-amino-pyrimidines), without the requirement for an oxidation step. 

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