The Photoreaction of Pyrylium Cation with Water: A DFT Study

Abstract: The photochemical reaction of pyrylium cation with water to give a cyclopentene derivative has been studied at the DFT/B3LYP/6-31G+(d,p) level of theory. The calculation is in agreement with an electrocyclic disrotatory reaction from the S1 singlet excited state, giving a cyclopentene epoxide cation that can react with very low activation energy (2 kJ mol-1) with water to give the corresponding adduct. CASSCF calculations allowed to identify a conical intersection in the S1 state, giving the cyclopentene epoxide cation.