Synthesis and crystallographic evaluation of diazenyl- and hydrazothiazoles. [5.5] sigmatropic rearrangement and formation of thiazolium bromide dihydrate derivatives

Abstract

In this investigation the synthesis of diazenylthiazoles (3a-e) by the reaction of arylthiosemicarbazides with ω-bromoacetophenones via Eschenmoser-coupling reaction in acetonitrile and equimolar amounts of triethylamine and triphenylphosphine. Upon heating 1,4-disubstituted thiosemicarbazides with ω-bromoacetophenones in absolute ethanol, hydrazothiazoles (16a-i) were precipitated. On the other hand, the reaction of arylthiosemicarbazides with ω-bromoacetophenones in refluxing ethanol yielded 2-amino-5-[4-aminophenyl]-4-phenylthiazolium bromide dihydrate derivatives (19a-g) via [5.5] sigmatropic shift. The studied products were further characterized by IR, 1H NMR, 13C NMR and mass spectrometry. X-ray single crystal of 3a and 16h showed that, the molecules crystallized in the triclinic crystal system, space group P21/c. Whereas the X-ray single crystal of 19b showed the molecule crystalized in orthorhombic, space group P212121. In the crystal of 19b, the lattice water and bromide ion associated through hydrogen bonded with thiazole-NH2.