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

Abstract

The mechanism for the photochemical cyclization reaction is studied theoretically using a model system of α-N-methylamidoacetophenone with the M06-L/6-311G(d,p) method. These model studies indicate that the preferred reaction pathway for α-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 α-N-alkylamino ketone systems. These computational observations are in agreement with the available experimental results.