Titanium(IV) isopropoxide-mediated dimerization of 2-(ferrocenylmethylidene)-1,3-dicarbonyl compounds

Diethyl 2-(ferrocenylmethylidene)malonate undergoes linear dimerization with formation of tetraethyl 2,3-diferrocenylbutane-1,1,4,4-tetracarboxylate when treated with EtMgBr in the presence of Ti(OiPr)4. Under similar conditions, ethyl (E)-2-(ferrocenylmethylidene)benzoylacetate and ethyl (E,Z)-2-(ferrocenylmethylidene)acetoacetate afford linear dimerization products (3,4-diferrocenyladipic acid derivatives) and intramolecular cyclization products of the latter (3,4-diferrocenylcyclopentanol derivatives). No products of the Kulinkovich reaction (hydroxycyclopropanation of the ester groups) were observed. The structures of the compounds obtained were established based on data from IR, 1H and 13C NMR spectroscopy, mass spectrometry and X-ray diffraction analysis. The mechanistic aspects of these reactions are discussed. Electrochemical properties of the compounds 7a, 10 and 12 were investigated using cyclic voltammetry, one step potential chronoamperometry and square wave voltammetry. Two electrochemical processes (I–II), attributed to the oxidations of the ferrocenes moieties, E0′(I), E0′(II), ΔE0′(II–I) and comproportionation constant Kcom are reported.