diazotized intermediates 2 and 3, the latter resulting from the acid ‐catalyzed hydrolysis of the lactonic ring of 2. The in situ formed diazonium salts react with aromatic amines (4) to afford a series of arylazothiophenes dyes in the form of their ammonium sulfate salts. With diazotized aniline, besides the normally expected phenylazothiophene 10 from the reaction with compound 1a, the corresponding product