Abstract
The flash photolysis of N-chloroacetyl-m-tyramine (V) in non-degassed aqueous solution afforded a transient absorption spectrum which consists of two groups with different intensities and life-times. The weak bands at 380, 386, and 412nm (τ=200-400μsec), which were also observed in the photolysis of N-acetyl-m-tyramine (VIII), correspond with the spectrum of the phenoxy radical.
The strong bands at 322 and 330nm decay according to a first-order kinetics (τ=530μsec in neutral solution, τ=48μsec in alkaline solution) and are attributed to the cyclohexa-2, 4-dienone (1, 2, 4, 5, 9, 9a-hexahydro-3H-3-benzazepin-2, 9-dione (X)), which is an intermediate of the photocyclization of V to 9-hydroxy-1, 2, 4, 5-tetrahydro-3H-3-benzazepin-2-one (VI). In conclusion, the photocyclization of V may be initiated by an electron transfer from the aromatic system to the chlorinated amide group, followed by ortho-cyclization of X, which aromatizes to yield VI.
