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.