High-Yielding Thermal [2+2] Addition to Fullerene

Significance

In most cases, fullerene functionalization reactions aiming at monofunctionalization yield a mixture of unfunctionalized C₆₀ and mono­adducts as well as higher adducts. This is a result of insufficient deactivation of the remaining [6,6] double bonds after the first addition and ultimately limits the yield of the reactions to ca. 40%. The authors present a thermal [2+2] cycloaddition that proceeds via a single-electron transfer step. The LUMO level of the products (2a-c) is raised compared to C₆₀, preventing further additions and leading to very high yield of the monoadduct (up to 97%).