Regioselective Oxazolination of C(70)(2-) and Formation of cis-1 C(70) Adduct with Respect to the Apical Pentagon

Oxazolination of C(70) has been achieved via the aerobic oxidation of C(70)(2-) in the presence of PhCN. Only one C(70) oxazoline regioisomer (1) is obtained, indicating that the oxazolination of C(70)(2-) occurs with an unusual regioselectivity. Further benzylation of 1(2-) with benzyl bromide leads to the formation of the first cis-1 C(70) 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 C(70) 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 C(70). The exhibited regioselectivity for the orientation of oxazolino group on C(70) is further rationalized with computational calculations, and a reaction mechanism for the oxazolination of C(70)(2-) is proposed.