Generation and characterization of alkyl-substituted m-xylylenes in fluid solution at room temperature

Fluoride ion induced generation of isobutylidene from isopropyl trimethylsilyl ketone enol triflate in the presence of 6,6-dimethylfulvene gives the [2.2]-m-cyclophane dimer of [alpha],[alpha],[alpha][prime],[alpha][prime]-tetramethyl-m-xylylene. When isobutylidene is added to 6,6-bis(trideuteriomethyl)fulvene, the [sup 13]C NMR spectrum of the dimer reveals three quaternary carbons in a 1:1:1 ratio, progressively shifted upfield to suggest that two dimers are formed. Saturation of the reactant solutions with dioxygen resulted in no dimer formation despite undimished loss of reactants. A control experiment indicated that dioxygen does not affect the formation of the methylenecyclopropane from cyclohexene and isobutylidene. Reaction of 6-cyclopropyl-6-methylfulvene with isobutylidene gave dimers with intact cyclopropane rings. Addition of isbutylidene 6-tert-butyl-6-methylfulvene resulted in a non-cyclophane dimer. 26 refs.