Nonclassical Abramov Products Formed on Orifices of Cage-Opened C₆₀ Derivatives

By nucleophilic addition of phosphite P(OMe)₃ to a cage-opened C₆₀ derivative, α-hydrophosphate and enol phosphate were obtained as kinetic and thermodynamic products, respectively. Different from classical Abramov products bearing a phosphorus-carbon bond, these products have a phosphorus-oxygen bond. The observed anomaly originates from the fully conjugated π system, which significantly stabilizes zwitterionic intermediates bearing a phosphorus-oxygen bond. The thus formed enol phosphate was found to exhibit an intense absorption band that extended to 730 nm, reflecting the intramolecular charge-transfer transitions. We also report domino phosphorylation reactions, which gave a cage-opened C₆₀ derivative bearing a direct P-C bond.