Fullerene lipids: synthesis of novel nitrogen-bridged

Reactions of methyl 6-azido-hexanoate, 8-azidooctanoate, and 12-azido-dodecanoate with [60]fullerene (1) gave the corresponding aza-[60]fullerene ester derivatives (2a-2c, 22-35% based on the amount of [60]fullerene reacted). The nitrogen atom is bonded to the [60]fullerene cage to yield a "[5,6]-open" type aza substructure. This was confirmed by the appearance of 30-31 sp2 signals at deltac 133-147 in the carbon nuclear magnetic resonance spectra. Reaction of methyl 11-azido-7-undecynoate with [60]fullerene furnished a mixture of aza-[60]fullerene (2d, 53%) and aziridine-[60]fullerene (2e, 38%) ester derivatives. Compound 2e was identified as the "[6,6]-closed" type aziridine-[60]fullerene derivative, which displayed 10 sp2 signals in the region deltac 140-145 and one signal at deltac 85.05 for the sp3 carbons of the cage. Refluxing a solution of compound 2d in toluene for 50 h gave about 50% yield of compound 2e, but not vice versa.