Density functional study on the tautomerism of pyrano[2,3-d]pyrimidine derivative: intramolecular and intermolecular proton transfer

Abstract

The proton transfer reaction mechanisms in the anhydrous and monohydrated forms of 7-amino-6-cyano-5-benzene-5H-pyrano[2,3-d]pyrimidine-2,4(1H,3H)-diones on the transition state structures have been carried out in the gas phase using the B3LYP density functional method. For the reaction, three possible mechanisms are considered and three pathways are subsequently discussed. Meanwhile, the assistant effects of water molecules in the 1st path, which is considered as the best way of proton transfer, have been discussed in detail with the number of water molecules increasing. Results reveal that water molecules hold a strong catalysis effect on the proton transfer, and the polar solvent is favorable to the stability of complexes.