Steroid–Fullerene Hybrids from Epiandrosterone: Synthesis, Characterization and Theoretical Study

Abstract

New hybrid fullerene–steroid derivatives were prepared by using the Bingel–Hirsch protocol, by treatment of [60]fullerene with malonates bearing the appropriate steroid moieties obtained, in turn, from the functionalization of epiandrosterone, an important naturally occurring steroid hormone. Monocycloadduct C 60 ‐steroid conjugates were obtained by functionalization of ring A or ring D of the steroid moiety. We have also described the multistep preparation of a [60]fullerene hybrid dumbbell endowed with two fullerene units connected through an epiandrosterone molecule by a cyclopropanation reaction. The new compounds have been spectroscopically characterized and their redox potentials, determined by cyclic voltammetry, reveal three reversible reduction waves for monocycloadducts ( 8 , 9 and 11 , 12 ), whereas dumbbell‐type derivative 10 exhibits the best electron‐accepting abilities of the Bingel‐type fullerene–steroid series. Theoretical calculations at semiempirical (AM1) and single point B3LYP‐D3/6‐31G+(d,p) levels have predicted the most stable conformations for the hybrid compounds and allow explaining the observed regioselectivity in the cyclopropanation reaction with dimalonate 7 during the synthesis of the dumbbell derivative.