Nitrile ketenimine tautomerism in substituted alkylidene malononitriles and alkylidene cyanoacetates: a characteristic UV absorption band

Abstract

Several alkylidene malononitriles (1b,1d,1e,2b and 4b) and alkylidene cyanoacetates (1a,2a and 4a) studied exhibit a long wavelength UV absorption band around 355 nm which shows a hyperchromic effect in the presence of ethanolic alkali. This band has been assigned to the ketenimine tautomer (5). Addition of water to1b,1e and 2b gives the corresponding pyridine diols (7a,7b and 8a) respectively. Similarly, addition of ethanol to 1e and 2b gave the corresponding ethoxypyridine derivatives (7c and 8b). Mechanism of formation of these compounds is discussed. Structures, as well as mechanism of formation of 1c, 7c and 10 obtained from 1b,1e and 2b respectively on standing at room temperature are also discussed.