The conversion of a pyrrole trimer derivative into a 4,5,6,7-tetra­hydro-4-­(pyrrol-2-yl)indol-7-yl­tosyl­aminoindole

Vilsmeier formyl­ation of trans-1-(4-methyl­phenyl­sulfonyl)-2,5-bis(pyrrol-2-yl)­pyrrolidine leads to cleavage of the central ring then a reclosure resulting in the formation of trans-N-[2-formyl-4-(5-formyl­pyrrol-2-yl)-4,5,6,7-tetra­hydro­indol-7-yl]­toluene­sulfon­amide, C₂₁H₂₁N₃O₄S.