AB initio calculations of Diels–Alder transition structures for hetero‐dienophile additions to cyclopentadiene

Abstract

AbstractTransition states for the hetero‐Diels–Alder addition of formaldehyde, formaldimine, diazene and nitrosyl hydride to cyclopentadiene were located with ab initio molecular orbital calculations. Asynchronous transition structures were located for the asymmetric hetero‐dienophiles, whereas the symmetrical hetero‐dienophile, cis‐diazene, produced a synchronous transition structure. The relative reactivities are in good agreement with the LUMO energies of the hetero‐dienophiles, and the transition states with the exo oxygen or nitrogen lone pairs have lower energies than the corresponding endo lone electron pair transition states. Endo/exo energy differences are much higher than in the addition of ethylene derivatives to cyclopentadiene.