2-Arylideneferroceno[e]cyclohexanones and related 3-aryl-3,3a,4,5-tetrahydroferroceno[g]indazoles: Synthesis, NMR-, DFT- and X-ray analysis

A series of 2-arylmethylideneferroceno[e]cyclohexanone was prepared by base-catalysed condensation of ferroceno[b]cyclohexanone with a variety of aryl aldehydes including formylferrocene. The decreased reactivity of these novel chalcones towards nucleophic reagents was interpreted by the comparison of DFT reactivity indices calculated for a selection of appropriate models. The conversion of five representative chalcones into ferroceno[g]indazoles of potential biological interest could be achieved by thiosemicarbazide-mediated cyclisation catalysed by hydrochloric acid in ethanol at reflux. The relative configurations of the novel chalcones and ferrocenoindazoles with the elements of planar-, helical- and central chirality were established by NMR methods and single-crystal X-ray diffraction.

Graphical abstractA series of ferroceno-fused chalcones and a selection of related indazoles were prepared. The reactivity of the novel chalcones was interpreted by DFT analysis. The relative configurations of the novel chalcones and ferrocenoindazoles with the elements of planar-, helical- and central chirality were established by NMR methods and single-crystal X-ray diffraction.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Preparation of ferroceno-fused chalcones from ferrocenocyclohexenone. ► Synthesis of ferroceno[g]indazoles with planar-, helical- and central chirality. ► Relative configuration of ferroceno[g]indazoles by NMR and XRD. ► Interpretation of different chalcone-reactivities by DFT analysis of LUMO and LUMO+1.