Photocyclyzation of 2-Azidobenzophenone

Thermolysis of 2-azidobenzophenone includes interaction between azido and carbonyl group resulting in 1,3-dipolar cyclization without nitrene intermediate formation. The reaction gives high yields of of 3-phenylanthranil. Photolysis of 2-azidobenzophenone as well as other aromatic azides gives singlet nitrenes as decomposition products. Small singlet-triplet gap reduces partly triplet forbiddance, and transition from the singlet into triplet state becames possible by means of intersystem crossing. Thus, two highly reactivie intermediates are formed under photolysis of the azide. They determine the subsequent reactions. The singlet nitrene can insert into carbonyl group giving 3-phenylanthranil, and the triplet nitrene can dimerize to form azocompound or abstract an hydrogen atom from solvent to turn into amines. In the 2-azidobenzophenone photolysis in acetonitrile we have found high yields of 3-phenylanthranil. The scheme becomes complicated by the 3-phenylanthranil secondary decomposition. No azocompound was found. We have proposed that there has place a transition of nitrene into low reactive conjugated biradical having electron density localized on nitrogen atom of nitrene and oxygen atom of carbonyl group. The biradical gives 3-phenylanthranil after of introsystem crossing into the singlet state.