Abstract: The photochemically generated singlet nitrene insertion into a double bond of an ortho-substituent and C=C bond at a benzene ring was investigated. The insertion into the double bond has to give a condensed heterocycle, but the insertion into a benzolic cycle produces an enlarged cycle up to unstable 1,2-didehydroazepin (DDHA). An addition of a nucleophilic agent required to form stable 3H-azepin, and upon an equilibrium "singlet nitrene -- DDHA" establishment it is shifted to the DDHA formation. It results in decreasing of the condensed heterocycle compound yield and increase of the 3H-azepin yield. To test this assumption we have investigated an addition of water molecules to the reaction system effect upon yields of 3H-azepin-2-one-3-carbonic acid and of 2,1-benzisoxazol-3(1H)-one in the course of the 2-azidobenzoic acid decomposition in aprotic solvents. It was stated that an increase of water amount in the reaction system will produce simultaneous increase both of the heterocycle compound and 3H-azepin. We have proposed that in the absence or small amount of nucleophilic additives 2,1-benzisoxazol-3(1H)-one can react with DDHA to form a complicated mixture of photolysis products, and thus to decrease of the heterocycle compound yields.