Synthesis via 2 atom combination

This is the most generally used approach for the synthesis of pyridazines, and has been adopted for the synthesis of phthalazines and cinnolines. In addition, several other condensed pju idazines were synthesized in this way. 

Classically, hydrazines cyclocondense with 1,4-difunctional reagents 28 to yield pyridazines 29 (2006TL149). 

Condensed pyridazines can be produced if R3 and R4 are parts of a ring system. 1,4-Diketones afford pyridazines, whereas 1,4-oxoenoic acid derivatives afford pyridazinones. 4-Oxo acid derivatives afford hexahy-dropyridazediones. 

The methylester of 2-oxo-3-pentenoic acid 43 with hydrazine derivatives was used to synthesize new pyridazinone derivatives through intermediate hydrazides 44 or 47 with subsequent cyclization. 

Almost all azolo[x,y-d]pyridazines have been prepared from the corresponding azole with two adjacent acyl, aroyl or carboxy derivatives. Thus, pyrrolo[3,4-d]pyridazines 50 are produced from hydrazine hydrate with 49 in ethanol at room temperature (2004BML203ll 

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