[70]Fullerene-fused lactones: synthesis, conversion and photovoltaic application.

Syntheses of [70]fullerene-fused lactones via palladium-catalysed annulation and 1,4-dipolar cycloaddition with complementary regioselectivities were achieved. Efficient retro Baeyer-Villiger reaction via electroreduction and trifluoromethanesulfonic anhydride treatment afforded [70]fullerene-fused ketones. Control experiments and theoretical calculations elucidated plausible reaction pathways. Representative products improved the organic photovoltaic efficiency to 18.27%.