A computational study of the mechanism of the photocyclization reaction of alpha-methylamino ketone

摘要

The mechanism for the photochemical cyclization reaction is studied theoretically using a model system of alpha-N-methylamidoacetophenone with the M06-L/6-311G(d,p) method. These model studies indicate that the preferred reaction pathway for alpha-N-methylamino ketone, which leads to the photocyclization product, is as follows: reactant (singlet) -> Franck-Condon region (triplet) -> local minimum (triplet) -> transition state (triplet) -> intersystem crossing -> intermediate (singlet) -> transition state (singlet) -> photoproduct (singlet). In other words, the intersystem crossing mechanism plays a decisive role in these photo-rearrangement reactions for alpha-N-alkylamino ketone systems. These computational observations are in agreement with the available experimental results.