Abstract
Oxidation of fullerenes is an important reaction to prepare key intermediates for the regioselective reactions and open-caged fullerenes. Although oxidation with meta-chloroperbenzoic acid (mCPBA) is a safe and easy way to obtain fullerene oxides,[1] the control of oxidation degree and improvement of regioselectivity of the multiple adducts have been a challenging task. To obtain regioselectively oxidized fullerene derivatives, we have investigated mCPBA oxidation of fulleroids bearing highly-reactive anti-Bredt olefin at the bridgehead.[2] The rate constant of the unsubsituted 1a was considerably larger than those of C60 and the fulleroids bearing mono-/di-phenyl substituents, respectively. The high reactivity of 1a was ascribed to the regioselective addition at the bridgehead double bond. Based on the APCI-MS and NMR analyses, it was found 1a gave ester products 2a and 2a' (Major:Minor = 3:1) containing meta-chlorobenzoate (mCB), whereas C60 gave a mixture of mono/di/tri-epoxides. This unusual electrophilic addition could be ascribed to the asymmetrical transition state[4] and subsequent ionic intermediate based on DFT calculation.
