2,5-Diamide-substituted five-membered heterocycles: Challenging molecular synthons

We describe synthetic routes for preparing previously unknown 2,5-diamide-substituted five-membered heterocycles based on the thiophene, pyrrole, and furan ring systems by exploiting Curtius-like rearrangement reactions. Conformation analysis of the 2,5-diamidothiophene derivatives identified a "closed" conformation, in which the two carbonyl O atoms are in close contact with the thiophene S atom.