Computational insight into the thermal reactivity of N-methyl-3-cyanomethyl-2-vinylindole. Competition between two pericyclic reactions

The direct cycloaddition of a N-methyl-3-cyanomethyl-2-vinylindole () with a N-methylmaleimide () is not observed. The in situ formation of an indolo-2,3-quinodimethane intermediate () leads instead of the normal cycloadduct to an 1,2,3,4-tetrahydrocarbazole (). To help our understanding of this reaction, we performed a DFT study. The formation of both, the direct cycloadduct () and the intermediate () are found to be not thermodynamically favorable. However, the small amount of formed in the medium reacts with the dienophile in this way explaining the regio-selectivity of the reaction. The diastereo-selectivity is finally explained by a Curtin–Hammett-type energy profile.