Heterocyclic synthesis with nitriles: new routes for synthesis of pyridazines, pyridines and their fused derivatives.

Phenylazocyanothioacetamide 1 reacts with malononitrile to afford the pyridinethione 4 which reacts with phenacylbromide to yield the pyridine-S-phenacyl derivative 6. 1 reacts with ethyl cyanoacetate to yield the pyridazine derivative, 8, and with phenacyl bromide to afford the N-phenacyl derivative 11, instead of the thiazole 10. Compound 11 afforded the pyrazolopyridine 13 on reaction with malononitrile while 10 was obtained on coupling of the thiazole 14 with diazotised aniline. Compound 10 reacts with malononitrile to afford the thiazolyl pyridazine 15. Compound 1 reacts with malononitrile dimer to afford the pyridopyridazine derivative 17a. 1 reacts also with active methylene heterocycles to afford the pyrazolo and thiazolo-fused pyridazines 20 and 23 respectively.