Pyridazine is an aromatic, heterocyclic, organic compound with the molecular formula . It contains a six-membered ring with two adjacent nitrogen atoms.
Occurrence
Pyridazines are rare in nature, possibly reflecting the scarcity of naturally occurring
hydrazines, common building blocks for the synthesis of these heterocycles. The pyridazine structure is a popular
pharmacophore which is found within a number of herbicides such as
credazine,
pyridafol and
pyridate. It is also found within the structure of several drugs such as
cefozopran,
cadralazine,
minaprine,
pipofezine, and
hydralazine.
Synthesis
In the course of his classic investigation on the Fischer indole synthesis, Emil Fischer prepared the first pyridazine via the condensation of
phenylhydrazine and
levulinic acid.
The parent heterocycle was first prepared by oxidation of
benzocinnoline to the pyridazinetetracarboxylic acid followed by
decarboxylation. A better route to this otherwise esoteric compound starts with the
maleic hydrazide. These heterocycles are often prepared via condensation of 1,4-
or 4-ketoacids with
.
