Synthesis and structural analysis of (e)-2-(2'-nitrovinyl)indoles from the corresponding 2-formylindole derivatives

Article abstract of DOI:10.1002/jhet.5570370543

Preparation of 2-formylindoles was carried out from the appropriate methylindole by oxidation with selenium dioxide and by Vilsmeier formylation. The 2-(2'-nitrovinyl)indoles have been obtained by condensation of 2-formylindoles with nitroalkanes in the presence of ammonium chloride in good yields. In this reaction, only the (E)-isomer of the 2-(2'-nitrovinyl)indoles was observed by ¹H nmr and NOE experiments. Evidence for an extended conjugation through the double bond and the nitro group can be evaluate by the deshielding effect on the olefinic protons. Moreover, the non-Beer's law behaviour in the uv-visible spectra suggest the existence of some sort of complex for these compounds.