Reaction of 1,1 '-Divinyl Ferrocene with One-Electron Oxidants: Entry into Functionalised [4]Ferrocenophanes and Observation of an Isotope-Dependent Chemoselectivity Effect

1,1'-Divinyl ferrocene (2) reacts with K-3[Fe(CN)(6)] under basic biphasic conditions to give a [4] ferrocenophane (4) in good yield. Incorporating deuterium labels into the internal positions of the vinyl groups of 2 affects the chemoselectivity of the reaction; thus under identical reaction conditions, [D-2]-2 reacts to provide a diol-functionalised [4]ferrocenophane, [D-2]-D/L-6 in addition to the expected keto-alcohol, [D-1]-4. Variants on this oneelectron oxidative cyclisation methodology can be used to give other [4]ferrocenophanes: thus, the reaction of 2 with CuCl2 in MeOH or iPrOH leads to dialkoxy [4]ferrocenophanes 19 and 20, respectively, whereas the reaction of 2 with benzyl carbamate in the presence of tBuOCI gives a bis(carbamate)[4]ferrocenophane, 21. Mechanisms to account for the formation of the products, the stereoselectivity. and the unusual isotope-dependent chemoselectivity in the reaction of 2 and [D-2]-2 with K-3[Fe(CN)(6)] are proposed.