Pyrrolo pyridazinones

Pyrrolo[3,4-d]pyridazinium salts, 2,3-dimethyl-synthesis, 4, 291 Pyrrolo[ 1,2-6]pyridazinones oxidation, 4, 298 Pyrrolo[2,3-6]pyridine, 1-acetyl-cycloaddition reactions, 4, 509 Pyrrolo[2,3-6]pyridine, 3-bromo-nitration, 4, 505... 

The synthesis of pyrrolo[2,3- 7 pyridazines can be achieved by starting either with pyridazine, a tetrazine, or a pyrrole. Pyridazinone 80 reacts with bromomethyl derivatives to give poor yields of 81 <1996H(43)1863> (Equation 34), while 5-acetyl-2-methyl-4-nitro-6-phenyl-3(2//)-pyridazinone, after treatment with sarcosine ethyl ester for a brief time at room temperature, followed by acid hydrolysis afforded a good yield of 82 (70%) <1994S669>. 

A series of 3-chloro-4-arylacetylenic pyridazines have been cyclized to the corresponding 5-aryl-furo(or pyrrolo or thia)[2,3-( ]pyridazinones <2006TL6125, 2006JMC3753>. 

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>. 

Many new pyridazine, cinnoline, and phthalazine syntheses relied on the use of hydrazine-based precursors. 4,5-Dihydro-3(2//)-pyridazinones were obtained by cyclization of hydrazine with Meldrum s acids <97SC3513>, and six-membered cyclic hydrazides 3 were obtained in very high diastereoselectivities by the coupling of azide-substituted bisfenol silanes) <97JOC5680>. PhSeBr-promoted cyclization of alkenyl phenylhydrazones led to tetrahydro-pyridazines <97T7311>, condensation of furofuranones and hydrazines led to pyrrolo[2,3-... 

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

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