Basicity of Secondary Penta-2,4-diynylamines and Their Reactions with Phenyl Isothiocyanate

Secondary penta-2,4-diynylamines were synthesized, and their pK_a(MeOH) values were obtained by means of nonaqueous potentiometric titration. The reactions of the amines with phenyl isothiocyanate, leading to 2-(phenylimino)-5-(prop-2-ynilidene)thiazolidines, were studied. The N-butyl- and N-benzylthiazolidines with alkyl substituents at the triple bond, formed by the reactions, undergo autooxidation into thiazolidin-4-ones.