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

Abstract

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 H-1 NMR, C-13 NMR, FT-IR, mass spectrometry and single crystal X-ray diffraction techniques.