Pyridazino pyridazinones

JOC6503>, and new pyridazino-psoralens 15 were prepared via a furan ring expansion reaction <05T4805>. The reaction of 3-acetylcoumarins with alloxan followed by NH2NH2 easily produced 3-(2-oxo-2//-chromen-3-yl)-6//,8//-pyrimido[4,5-c]pyridazine-5,7-diones <05JHC1223>. Furano- and pyrano[2,3-c]pyridazines 17 and 18a,b as well as substituted quinolines were conveniently prepared from pyridazinone 16 and vinyl- and allyltriphenyl-phosphonium salts <05HAC56>. 

A synthetic approach designed to produce pyridazino[4,5-c]pyridazinones unexpectedly yields pyrrolopyridazines, although in poor yields. The acid-catalyzed reaction between the hydrazine (101) and ketodiesters (102) results in formation of the pyrrolo[2,3-d]pyridazine (103) (Equation (31)) <92JHC1313>. 

Heating of 1-methyl-l-(3-pyridazinyl)hydrazines (15) or their hydrazones at 240-250°C gives exclusively a pyridazino[3,4-t]pyridazine derivative (16). This reaction probably proceeds via a pyridazinone intermediate (17) which undergoes an intramolecular Michael addition leading to the pyridazino[3,4-c]pyridazine (16) (Scheme 3) <89T1793>. 

Similar products (220) and (221) were obtained by the intramolecular cyclization of 4-chloro-5-(2-chloroethylamino)-2-methyl-3(2//)-pyridazinone with sodium sulfide. The isomeric pyridazino[4,5- ][l,4]thiazinone has been prepared by cyclocondensation of 4,5-dichloro-2-methyl-3(2//)-pyr-idazinone with sodium 2-aminothioethylate <82CPB1030>. Although the reaction is similar to the one mentioned above, in this case the protecting groups could not be cleaved in the way reported by Zara-Kaczian and Matyus <93H(36)519>. 

The reactivity of pyridazines in Pd-catalyzed reactions was of interest. For example, the Heck alkenylation at C5 of 6-phenyl-3(2//)-pyridazinones was investigated, with the aim of suppressing production of 4-phenyl-6-substituted-2-phthalazinone byproducts <04TL3459>. In another study, the reactivity of 5-iodopyridazin-3(2f/)-ones in Pd-catalyzed reactions was investigated to develop an efficient route to 2,5-disubstituted pyridazin-3(2/f)-ones <04T12177>. Other pyridazine syntheses relied on condensation approaches. Benzo[g]pyridazino[l,2-i>]-phthalazine-6,13-diones 16 and 17 related to certain anthracyclinones were obtained by cycloaddition of 1,3-dienes to benzo[g]phthalazine-l,4-dione <04H(63)1299>, and pyridazine C-nucleosides synthesized by 14-i-2 cyclocondensation of alkynyl C-nucleosides with substituted tetrazines afforded, upon extrusion of a nitrogen atom, pyrrole C-nucleosides in good yields... 

Other 1,2-diazines synthesized included 4-amino-3-cinnolinecarboxylic acids <97PHA91 >, I -aryl-6-chloro-l,4-dihydro-4-oxothieno[2,3-c]pyridazine-3-carboxylic acids <97JPR284>, 2H-benzo[2,3-g]pyridazino[4,5-<7,e]quinolin-3-ones <97M681>, 3-chloro-4-carbamoyl-5-aryl-6-methylpyridazine N-oxides <97F67>, 2-aroyl-6-(hetero substituted)-3(2//)-pyridazinones <97HCM267>, and 5-(4-hydroxycinnolin-3-yl)tetrazoles 2-methyl-5-(4-acetoxycinnolin-3-yl)-... 

Cyclization of the halohydrazones 14 affords the pyrrolo[2,3-. 

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