Pyridazine-3,6-diol ring

Acetic acid acetic anhydride Pyridazin-3,6-diol ring from dicarboxylic acids... 

Diols or 1,2-dithiols (or their sodium salts) in a basic environment react as nucleophiles towards dihalides, especially when the latter are attached to electron-deficient rings such as pyrazine or pyridazine. HMPT promotes this cyclization. 

Apart from the A-methylated compound,1 examples for derivatives of the fully conjugated pyridazino[4,3-c]pyridazine or the unsubstituted compound 1 itself are not known. Attempts to synthesize 4,8-diphenylpyridazino[4,3-c]pyridazine-3,7-diol (3) by reacting pulvinic acid lactone 2 with an excess of hydrazine failed, instead 6-benzyl-4-phenylpyridazine-3,5-diol (4) was produced. The reaction is thought to proceed via the attack of hydrazine on one lactone ring and water on the other, followed by decarboxylation.4... 

Phenylpyridazino[4,5-r/]pyridazine-1,4-diol (1) is unstable towards acidic reagents. When treated with dilute hydrochloric acid, ring contraction to 6-amino-1-phenylpyrrolo-[3,4-d]pyridazine-5,7-dione (2) occurs.10... 

When the hydrazine adduct of 2-phenylpyrimido[4,5-d]pyridazine-5,8-diol (7) was treated with hydrochloric acid, the expected 2-phenylpyrimido[4.5-d]pyridazine-5,8-diol (8) was not formed. Instead the pyridazine ring underwent ring contraction leading to 9.54... 

When pyrimido[4,5-r/]pyridazine-2.4-diol is treated with concentrated aqueous ammonia at elevated temperature the pyrimidine ring is cleaved to give 5-aminopyridazine-4-carboxylic acid quantitatively.57... 

Some reactions of 231 preserve the furoxan ring. With hydrazine it forms the fused pyridazine 230, and a number of other diacylfuroxans give analogous products (see Section IV,E). The diketone can be reduced to the diol... 

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