Understanding the Intramolecular Diels‐Alder Reactions of N‐Substituted N‐Allyl‐Furfurylamines: An MEDT Study

Abstract

AbstractThe intramolecular Diels‐Alder (IMDA) reactions of N‐allyl‐furfurylamine (1a) and N‐trityl‐allyl‐furfurylamine (1b), were studied within the molecular electron density theory (MEDT) using density functional theory method [B3LYP/6‐31G(d)]. In spite of the high activation enthalpies, the low unfavourable activation entropies associated to these intramolecular processes permit these IMDA reactions to take place. The IMDA reaction of 1a is thermodynamically unfavourable. The presence of the bulky −CPh3 group in the amine nitrogen atom that destabilises the extended conformation of 1b turns the process into an exergonic one. This behaviour does not only affect the thermochemistry of the reaction, but also the kinetic parameters, thus accelerating the reaction. Electron localisation function topological analysis of the C−C single bond formation along the IMDA reaction of 1a shows a bonding pattern similar to non‐polar intermolecular Diels‐Alder reactions. The present MEDT study explains the experimental results; although the steric buttress is able to change the direction of these reversible IMDA reactions, this change is only possible due to the aromatic nature of the furanyl diene system.