Three-component coupling reaction of the C60 fullerene, indole and propargyl bromide: a theoretical study

In the current research, a three component reaction [reported experimentally by Li et al. (Org Lett 19:1192-1195, 2017)] between the C-60 fullerene, indole and propargyl bromide is studied theoretically. According to the proposed mechanism in the experimental work, nucleophilic attack of indole anion (Ind(-)) to C-60 affords fulleroindole monoanion (FI) as an intermediate, which experiences another nucleophilic attack on certain primary organohalides to generate the corresponding 1,4-(3-indole)(organo)[60]fullerenes. To investigate the reaction from the mechanistic point of view, certain competition paths were designed between the starting materials in each step and some theoretical quantities were obtained and elucidated. In consistence with the experimental findings, the local Fukui as well as Parr functions reactivity indices confirmed the observed regioselectivity in the first step of the reaction. These local reactivity indices implied also that in the nucleophilic attack of FI on the organohalides, one of the ortho positions is more nucleophilically activated than para position. A PES analysis on the proposed reaction paths revealed a good agreement with the experimental findings. The electron transfer studies and the computation of molecular electrostatic potential (MEP) map of the transition states suggested that in addition to the steric repulsions, the electronic repulsions in the ortho positions determines the para-selectivity preference over the ortho ones.