FeCl3‐Catalyzed Formal [3+2] Cyclodimerization of 4‐Carbonyl‐1,2‐diaza‐1,3‐dienes.

Substituted 1‐aminopyrroles are easily accessible by iron‐catalyzed cascade reaction of 1,2‐diaza‐1,3‐dienes. Mechanistically, a formal [3+2] cyclodimerization is hypothesized to proceed through a [4+2] cyclodimerization of 4‐substitued 1,2‐diaza‐1,3‐dienes followed by intramolecular ring closure to fused diaziridin‐pyrrolines which is successively opened to undergo a ring contraction process and consequently generate the desired pyrrole moiety. The presence of activated hydrogen in the terminal position of the azo‐enic moiety is crucial for the synthesis of pyrroles. [ABSTRACT FROM AUTHOR]