Pyridazine-3,6-diones

Pyridazine-3,6-diones (diazaquinones) are prepared from cyclic hydrazides by oxidation with lead tetraacetate or other oxidizing agents, such as r-butyl hypochlorite, chlorine or nickel peroxide. 

Pyridazine-3,6-dione, 3,6-dihydro-[4- 2] cycloaddition, 3, 38 ring contraction, 4, 148 synthesis, 3, 38... 

Six-membered ring ADC compounds can be generated by oxidation of the corresponding cyclic hydrazides. Pyridazine-3,6-dione (12) and phthalazine-1,4-dione (13, R = H), often called diazaquinones,4 are stable in solution only at low temperature, but can be generated, and intercepted at higher temperatures.39-43 Fusion of an extra benzene ring increases stability44 and the tetracyclic compound 14 is relatively stable.45 Substituted phthala-zine-l,4-diones have been widely studied because of their involvement in... 

A 1,2-diazetidine has been proposed as an intermediate in the reaction of pyridazine-3,6-dione (12) with styrene.87 The observed product was thought to arise from addition of water to the 1,2-diazetidine, although the alternative more likely explanation involving a dipolar intermediate (cf. Scheme 5) was apparently not considered. In the photochemical reaction of styrene with DEAZD, a 1,2-diazetidine structure was tentatively assigned to a minor product.88 Attempted photochemical [2 + 2] cycloaddition of DEAZD to other olefins failed to give any 1,2-diazetidines.88... 

Hydroxypyridazine 1-oxide is readily brominated to give the 4,6-dibromo derivative.301 This is another example of a- and y-activation for electrophilic substitution by an N-oxide group since the des-N-oxide does not react. Chlorination proceeds similarly, but upon nitration only the 4-nitro derivative is formed.302 5-Hydroxypyridazine 1-oxide is also brominated to give the 4,6-dibromo derivative if position 6 is blocked, the corresponding 4-bromo derivative is formed.303 1,2-Disubstituted 5-bromo-pyridazine-3,6-diones are brominated to 4,5-dibromo compounds.304... 

C15H1eBrN302, 1 -(p-Bromophenyl)-2-methyl-4-diethylamino-pyridazine-3,6-dione, 45B, 226... 

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