Structure of the intermediate in the synthesis of 6-methyl-2-oxo-1,2- dihydropyridine-3-carbonitrile

Abstract

4-(Dimethylamino)but-3-en-2-one 1a reacted with malononitrile 2a affording (2E,4E)-2-cyano-5-dimethylamino)hexa-2,4-dienamide 6aa that was isolated as two isomers, 1-s-cis and 1-s-trans 6aa as confirmed by X-ray diffraction analysis. Acid-induced cyclization of 1-s-cis 6aa gave the known 1,2-dihydro-6-methyl-2- oxopyridine-3-carbonitrile 3aa, but not 1,2-dihydro-4-methyl-2-oxopyridine-3- carbonitrile 9aa as reported previously. The mechanistic pathway of the 2-pyridone ring formation is discussed.