Regioselective Oxazolination of C₇₀^2– and Formation of cis-1 C₇₀ Adduct with Respect to the Apical Pentagon

Oxazolination of C₇₀ has been achieved via the aerobic oxidation of C₇₀^2– in the presence of PhCN. Only one C₇₀ oxazoline regioisomer (1) is obtained, indicating that the oxazolination of C₇₀^2– occurs with an unusual regioselectivity. Further benzylation of 1^2– with benzyl bromide leads to the formation of the first cis-1 C₇₀ derivative with respect to the apical pentagon (2), as shown by the X-ray single-crystal structure and various spectral characterizations. The structure of the obtained C₇₀ oxazoline (1) is resolved with H/D labeling benzylation and HMBC (heteronuclear multiple bond coherence) NMR on the basis of the structure of 2. The result shows that for compound 1, the O atom is selectively bonded to the C1, while the N atom is bonded to the C2 of C₇₀. The exhibited regioselectivity for the orientation of oxazolino group on C₇₀ is further rationalized with computational calculations, and a reaction mechanism for the oxazolination of C₇₀^2– is proposed.