Pyrimido 4,5-d pyridazines

Pyrimidin-4-one, 2,5,6-triamino- N NMR, 3, 64 (78HCA2108) Pyrimido[4,5-d]pyridazin-5-amine, JV-benzyl-8-chloro-2-phenyl-pXa, UV, 3, 337 <76BSF(2)1549) Pyrimido[4,5-d]pyridazin-5-amine, JV-butyl-8-chloro-2-phenyl-... 

Pyrimido[4,5-d]pyridazine-5,8-dione, 2-aryl-chlorination, 3, 345 Pyrimido[ 1,2-6]pyridazine-2,4-diones synthesis, 3, 355... 

Pyrimido[4,5-c]pyridazine-5,7-diones cleavage, 3, 344 synthesis, 3, 356, 357 Pyrimido[4,5-d]pyridazine-2,4-diones cleavage, 3, 347... 

Pyrimido[5,4-c]pyridazin-8(2i/)-one, 6- N,N-dimethylamino)-2-phenyl-synthesis, 3, 357 Pyrimido[l, 2-6]pyridazin-2-ones H NMR, 3, 333 IR spectra, 3, 335 synthesis, 3, 354, 355 Pyrimido[ 1,2-6]pyridazin-4-ones synthesis, 3, 354, 355 Pyrimido[4,5-c]pyridazinones chlorination, 3, 344 Pyrimido[4,5-d]pyridazin-5-ones... 

Pyrimido[4,5-d]pyridazine-2,5-diones were synthesized in a similar manner, employing several hydrazines (R3 = H, Me, Ph) for the nucleophilic substitution prior to cyclative cleavage. Due to the high nucleophilicity of the hydrazines, reaction times for the substitution step could be reduced to 30 min. In the case of phe-nylhydrazine, concomitant cyclization could not be avoided, which led to very low overall yields of the isolated products. 

Pyrimido[4,5-d]pyridazine derivatives are readily cleaved under both acidic and basic conditions. Reaction of 2-phenyl-5,8-dimorpholinopyrimido[4,5-hydrochloric acid gives a mixture of four isolated products 2-phenyl-8-morpholinopyrimido[4,5-d]pyridazin-5(6//)-one (96), 4-hydroxy-6-morpholinopyridazin-3(2jy>one (97), 4-amino-5-formyl-3,6-dimorpholinopyridazine (98) and benzoic acid (99). 

A mechanism has been proposed to account for the formation of each of these products (72YZ1312). Pyrimido[4,5-d]pyridazine-2,4-dione (85) is cleaved by 10% aqueous sodium hydroxide to give 5-hydroxypyridazine-4-carboxylic acid (100). Cleavage with concentrated ammonium hydroxide also occurs, yielding 5-aminopyridazine-4-carboxylic acid (101) (68JHC845). 

Most pyrimido[4,5-d]pyridazines are prepared from 4,5-disubstituted pyridazine precursors. The versatile intermediate pyrimido[4,5-cf]pyridazine-2,4-dione (85) can readily be formed in high yield from pyridazine-4,5-dicarboxamide (196) by reaction with sodium hypobromite in a Hofmann type reaction (68JHC53). 

H NMR, 3, 335 <82JOC674> Pyrimido[4,5-d]pyridazin-5-one, 2-amino-6-methyl- H NMR, 3, 336 <76BSF(2)1549> Pyrimido[4,5-d]pyridazin-5-one, 2-amino-6-methyl-4-phenyl-... 

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