A series of phenolic azo compounds 7a-e were prepared by coupling the thienyldiazonium sulfate 5 of the title 2-aminothiophene 4 with selected diversely substituted phenolic and naphtholic derivatives. The newly prepared azo dyes were characterized by their physical, elemental and spectroscopic data. In some cases, the two dimension nuclear magnetic resonance (2D-NMR) techniques such as correlation spectroscopy (COSY), heteronuclear single quantum coherence (HSQC) and heteronuclear multiple bond coherence (HMBC) were used to secure the structural assignments. It was found that the substitution pattern and the stoichiometry of each of the reactions were strongly dependent on the nature of the substituents initially present in the coupler’s ring. The regio-orientations of the electrophilic aromatic substitutions (SEAr) of the thienyldiazonium ion on the various aromatic rings of the couplers were clearly established by the 1H-NMR experiments and by the characteristic fragmentations’ patterns observed on the higher resolution electron impact mass spectroscopy (HREIMS) spectra. It was assumed that these reactions proceed via the highly unstable Wheland complexes which ultimately eliminate the protons under the catalytic action of a base.
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