The photochemical isomerization of 2-picoline N-oxide, 4,6-dimethylpyrimidine N-oxide and 2-methoxypyrimidine N-oxide. A DFT study

The photochemical isomerization of 2-picoline N-oxide showed the formation of the corresponding oxaziridine derivatives that can be converted into oxazepines. Both the oxazepines can be converted into the corresponding pyrrole derivatives. The preferential formation of 5-methyl-2-formylpyrrole can be explained by using CASSCF calculations. In this case, only one conical intersection can be determined, favoring the formation of 2-methyl-7-oxa-1-azabicyclo[4.1.0]hepta-2,4-diene. DFT calculations on the photochemical isomerization of 4,6-dimethylpyrimidine N-oxide showed that both the corresponding oxaziridine and oxadiazepine derivatives can be formed. However, the most stable oxaziridine was that allowing the formation of the minor product obtained in the reaction. This behavior can be explained considering the possible conical intersections from the excited singlet state and the oxazidines. DFT calculations on 2-methoxypyrimidine N-oxide are in agreement with the formation of the corresponding oxaziridine and oxadiazepine derivatives.