As exemplified with the morpholino derivatives 7, N, N-disubstituted 2-aminothiophenes couple, depending on the substitution pattern at C (5), with aryldiazonium salts 1 either at their C (3) or C (5) position yielding the corresponding 3-arylazo-2-morpholinothiophenes 9 or, under elimination of the substituent at C (5), 5-arylazo-2-morpholinothiophenes 10. This reaction contrasts to the behaviour of 5-morpholinothiazoles 8 and dimethylaniline 13 ...