Cascade reactions of diazocarbonyl compounds with pyridinium aroylmethylides accompanied by water or benzoic acid elimination in the cyclocondensation step

The reaction of pyridinium aroylmethylides with diazocarbonyl compounds proceeds as a multistep process involving three ylide molecules and one diazo compound molecule. As a result, intermediate functionally substituted azines, if they contain carbonyl groups and reactive methylene fragment, undergo intramolecular cyclocondensation to form tri- and tetrasubstituted pyridazines. Depending on stereochemistry of cyclic ketols formed, water or benzoic acid is eliminated to form tetra- or trisubstituted pyridazines, respectively. The regularities of reactions of pyridinium ylides with diazo compounds are discussed depending on the nature of substituents in the both substrates and reaction conditions.