Vicinal multifunctional compounds. Tautomerism and isomerism in the condensation products of 2-hydroxyimino-3-oxobutanal or 3-hydroxyiminopentane-2,4-dione with benzylamines

The blue products from the condensation of 2-hydroxyimino-3-oxobutanal (1a) with benzylamine and a series of its substituted derivatives have been isolated and identified as (Z)-α-nitroso-β-enaminones (3a). In contrast, condensation of 3-hydroxyiminopentane-2,4-dione (1b) with benzylamines gave colourless α-hydroxyimino-β-imino-ketones (2b). In both series there exist in solution equilibria between the nitroso-enaminones (3) and hydroxyimino-ketones (2). The configurational problems and the influence of steric and solvent effects on the distribution of tautomers and isomers at equilibrium are discussed.