Synthesis of Methylene Bridged Bis-pyrrolo[3,2-c]carbazoles via an Unusual Vilsmeier–Haack Product of N-Ethylcarbazole

The unexpected result for the formylation of N-ethylcarbazole under the Vilsmeier–Haack conditions (POCl₃/DMF) led to the synthesis of novel methylene bridged bis-pyrrolo[3,2-c]carbazoles via Hemetsberger indole synthesis was reported. A plausible mechanism for the formation of unexpectedly synthesized 7,7′-methylene bis(9-ethyl-9H-carbazole-3-carbaldehyde) 4 was postulated. The full characterization data of dicarbazolylmethane 4 and the bis-pyrrolo carbazoles 10a-b were obtained by utilizing ¹H NMR, ¹³C NMR, FT-IR, mass spectrometry and single crystal X-ray diffraction techniques.