Mannich Reaction Involving 6-Amino-4-methyl-2-(thio)oxo-1,2-dihydropyridine-3,5-dicarbonitriles

The reaction of (1-ethoxyethylidene)malononitrile with cyanoacetamide or cyanothioacetamide has yielded 6-amino-4-methyl-2-(thio)oxo-1,2-dihydropyridine-3,5-dicarbonitriles. The resulting pyridine derivatives enter into the aminomethylation reaction with an excess of formaldehyde and primary amines with the formation of previously unknown 8-methyl-6-oxo-3-R-1,3,4,6-tetrahydro-2H-pyrido[1,2-a][1,3,5]triazine-7,9-dicarbonitriles. Further treatment of 6-amino-4-methyl-2-thioxo-1,2-dihydropyridine-3,5-dicarbonitrile and its oxygen analog with excess of formaldehyde has led to the formation of 3,10-dimethyl-1,8-dithioxo-5,6,12,13-tetrahydro-1H,8H-dipyrido[1,2-a:1′,2′-e][1,3,5,7]tetrazocin-2,4,9,11-tetracarbonitrile and 6,6′-[methylenedi(imino)]bis(4-methyl-2-oxo-1,2-dihydropyridine-3,5-dicarbonitrile), respectively. These compounds have shown a pronounced antidote effect against the herbicide 2,4-D (2,4-dichlorophenoxyacetic acid) in laboratory and field experiments on sunflower seedlings. Furthermore, 6-amino-4-methyl-2-oxo-1,2-dihydropyridine-3,5-dicarbonitrile has exhibited pronounced anticorrosion properties, acting as an adsorption-type corrosion inhibitor. The mechanism of the anticorrosion action has been investigated in detail using X-ray photoelectron spectroscopy.