o-Aminonitrile in Heterocylic Chemistry: Synthesis of Thienopyridine, Pyridothienopyrimidine, Pyridothieno[1,2,4]triazolopyrimidine, Pyridothienopyridine Derivatives

Abstract: Reaction of thienopyridine derivatives 1a,b with triethyl orthoformate gave 3-(ethoxymethyleneamino)thienopyri-dine-2-carbonitrile derivatives 2a,b. Compounds 2a,b were reacted with hydrazine hydrate to give pyrido-theinopyrimidine derivatives 3a,b, which were reacted with triethyl orthoformate, acetyl chloride and diethyl oxalate to give pyridothi-eno[1,2,4]triazolopyrimidine derivatives (4-6). Pyridothieno-pyrimidine (7-12) and pyridothieno-pyridine (13, 14) were synthesized. Diazotization of 1a,b followed by coupling with ethyl cyanoacetate and malononitrile gave hydrazono derivatives (16, 17) which were cyclized with hydrazine hydrate and hydroxylamine hydrochloride to afford pyrazole derivatives (18, 19) and isoxazole derivatives 20a,b, respectively. All newly synthesized structures were established via elemental analysis and spectral data.