Synthesis, X-ray and Fluorescence Characteristics of Pyrimido[5,4-e]thiazolo[3,2-a]pyrimidine as a Novel Heterocyclic System.

Derivatives of a new heterocyclic system, pyrimido[5,4-e]thiazolo[3,2-a]pyrimidine 3, were prepared by sequential treatment of ethyl 4-chloro-2-(methylthio)pyrimidine-5-carboxylate 1 with 4,5-dihydrothiazol-2-amine 2 and various secondary amines. Single crystal X-ray analysis confirmed the structure of the regioisomer 3. The photophysical characterization of these new compounds was performed by UV/VIS absorption and fluorescence emission spectroscopy. Out of six derivatives studied, only four products 4a-d showed relatively strong fluorescence intensity. The relevant photophysical parameters for all derivatives in this series, including quantum yields and Stokes shifts for the best fluorophores are given.