Is corannulene a better diene or dienophile? A DFT analysis

Abstract

Diels Alder reactivity of corannulene has been probed using density functional theory (DFT) at B3LYP/6-31G level by employing it both as a diene and a dienophile in cycloaddition with ethylene and 1,3-butadiene as typical partners. Computations reveal that corannulene acts better as a dienophile than as a diene and as a dienophile it undergoes normal electron demand type addition with 1,3-butadiene, and as a diene corannulene undergoes inverse electron demand type addition with ethylene. When employed as a dienophile the addition takes place preferentially in the rim position than in the spoke position due to strong steric and electronic reasons. Further in the rim addition rim exo approach is favored kinetically and thermodynamically. As a diene, corannulene shows regioselectivity for rim-spoke addition over spoke-spoke addition. Concerted type cycloadditions have been studied and the reactions are seen to take place preferentially on the convex face. The effect of substituents in butadiene on the reactivity and the reaction of butadiene-pentaindenocorannulene (an extended corannulene) system has been investigated for the most favorable rim exo positions.