| Abstract
| - The site of nucleophilic addition to five-membered heterocyclic 2,3-diones (4-iminomethylfuran-2,3-dione A1 and 4-formyl-pyrrole-2,3-dione B1) is studied by density functional theory calculations(B3LYP/6-31G*) with water as the nucleophile. Both uncatalyzed and water-assisted 1,2-additionto the lactone (lactam) and the keto carbonyl group, and conjugate addition to C5 of the heterocycleand the heteroatom of the 4-iminomethyl (formyl) moiety are considered. In addition, concertedand stepwise ring fission of the lactone (lactam) ring is also treated. The effect of solvation (aqueoussolution) is taken into account by the polarizable continuum model (PCM) and the Poisson−Boltzmann SCRF method (PB-SCRF), as well as explicit water molecules. Only this latter approachyields meaningful activation free energies. Barriers for addition of H2O increase in the order 1,4-addition to C5< addition to the lactone (lactam) carbonyl < hydration of the 3-keto group. Noreaction path for concerted water-assisted ring opening could be found.
|
