Studies on cyanine dyes. IV. Synthesis of new styryl oxa-cyanine dyes

The condensation reaction of benzoxazole-2-carboxaldehyde (I) with quaternary salts of heterocyclic compounds, in the presence of piperidine as a catalyst, afforded styryl cyanines (II). Interaction of (I) with the non-quaternised heterocyclic compounds at a longer time gave the corresponding dimethine bases (III). On the other hand, benzoxazole-2-carboxaldehyde-3-ethiodide (IV) interacted with quaternised and non-quaternised heterocyclic compounds achieved styryl cyanines of the type (V) and (VI), respectively. Absorption spectra for these compounds in EtOH are discussed.