Unexpected synthesis of a novel heterocyclic system – (7E,10aE)-2,7-Dimethylfuro[3′,4′:6,7]cycloocta[1,2,3-cd]indole-8,10(2H,6H)-dione

•Novel furocycloocta[c,d]indole heterocyclic system was synthesized.•The Stobbe condensation was used on the first two stages.•The structure was confirmed by 1H, 13C NMR and single crystal X-ray diffraction.