Chiral self-recognition in a bispericyclic cyclodimerisation reaction of 1-azadienes†

Abstract

Hermaphroditism of molecules: as in nature some species behave as male or female depending on the environment, herein we report a bispericyclic dimerisation of cyclic 1-azadienes where a molecule can behave as either diene or dienophile, depending on its location at the transition state. In a symmetrical reactive complex, here represented by an arbitrary reference system, a molecule that is positioned on top acts as the diene unit, while the dienophile partner is the one situated at the bottom. In addition, a strong chiral self-recognition phenomenon is observed, where each enantiomer within a racemic mixture of chiral 1-azadienes exclusively recognises itself. In order to shed some light into the understanding of the chiral self-recognition effect, an extensive DFT study of the reaction pathway is provided, concluding that a combination of attractive π-stacking forces and repulsive steric interactions is at the origin of the high stereospecificity of the reaction.