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)

Through extended S(N)2' 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(N)2' 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.