70Fullerene (C70)-fused five-membered-ring lactones were synthesized via manganese(III) acetate (Mn(OAc)3)- or air-promoted protocols. Under Mn(OAc)3-promoted conditions, three isomers 2a-c were obtained. In contrast, the single isomer 2a was regioselectively generated under aerobic conditions, representing a distinctive phenomenon in the exohedral functionalization of C70. The electrochemically generated dianion from lactone 2a was further reacted with different electrophiles to regioselectively produce either monoalkylated 1,2-adducts (4a-c) or bisalkylated 2,5-adducts (5a-c). Notably, the unprecedented C70-fused cyclobutanone 6a was readily obtained by treatment with an acyl chloride, and its application as a third component achieved an improved power conversion efficiency of 19.0% in organic photovoltaics.
Qiu et al. (Mon,) studied this question.