Formation of [18]trannulenes derived via Bingel reactions between C60F18O isomers and CHBr(CO2Et)2 and between C60F18 and CHX(CO2R)2 (X = Br, Cl; R = Me, Et)

Abstract

Through extended S_N2′ nucleophilic substitution of three fluorine atoms in two isomers of C₆₀F₁₈O by alkyl halogenomalonate anions ⁻CBr(CO₂Et)₂, (obtained from diethyl bromomalonate in the presence of DBU) we have prepared and characterised the [18]trannulenes, C₆₀F₁₅O[CBr(CO₂Et)₂]₃. Likewise we have prepared [18]trannulenes by the reactions between C₆₀F₁₈ and either ⁻CBr(CO₂Me)₂ or ⁻CCl(CO₂Et)₂ (obtained from the corresponding esters 1, 2 and DBU). The formation of the trannulenes from either 1 or 2 shows that the CBr(CO₂Me)₂ and CCl(CO₂Et)₂ substituents, though smaller than CBr(CO₂Et)₂ are still large enough to bring about the extended S_N2′ substitution, rather than direct nucleophilic substitution. The products from the oxides show that oxygen does not inhibit trannulene formation either sterically or electronically. Each derivative has the brilliant emerald-green colour of the corresponding [18]trannulene prepared from C₆₀F₁₈ and diethyl bromomalonate, arising from the presence of bands at ca. 615 and 660 nm; minor variations in wavenumber and relative intensities occur according to the derivative. Under less forcing conditions, mono- and bis-substitution products were obtained from the more available symmetrical oxide and from the reaction of the chloro- and bromo-esters with C₆₀F₁₈.