Synthesis of novel 5‐chlorinated 2‐aminothiophenes using 2,5‐dimethylpyrrole as an amine protecting group

Abstract

Abstractmagnified imageA new synthetic methodology towards substituted 2‐amino‐5‐chlorothiophenes is described. Compounds of this type are important as building blocks for oligomers used in polymer research. Easily available 2‐aminothiophenes underwent Paal‐Knorr reaction to protect the free amino group before electrophilic substitution. Although the chlorination was predicted to proceed at the thiophene ring, only free positions of 2,5‐dimethylpyrrole were substituted. To direct chlorination to the thiophene ring acetamido derivative was prepared first and then chlorinated. Transamination with hexane‐2,5‐dione created a 2,5‐dimethyl pyrrole ring from the acetamido group. In the final step, after treatment with hydroxylamine dihydrochloride, the pyrrole ring is removed and a free amino group is regenerated.