The electron ionization (EI) and collision-induced dissociation (CID) spectra of substituted N-(ortho-cyclopropylphenyl)benzamides 1-7 and N-[ortho-(1-methylcyclopropyl)phenyl]benzamides 8-12 were recorded. In addition to routine bond cleavages, the molecular ions (M+) of 1-12 undergo cyclization into the corresponding 3-aryl-1-alkyl-1-ethyl-1H-benzoxazines and isomeric 5-ethyl-2-oxodibenzoazepines. The presence of a methyl group in the cyclopropyl ring (compounds 8-12) makes the formation of 5-ethyl-2-oxodibenzoazepine less favorable. In accord with mass spectrometric predictions, compound 13 (3-p-tolyl-1-ethyl-1H-benzoxazine) was obtained as a major product of the reaction of N-(ortho-cyclopropylphenyl)-4-methylbenzamide 1 with sulfuric acid. Traces of 5-ethyl-2-oxodibenzoazepine were also detected in gas chromatography-mass spectrometry (GC-MS) analysis of the reaction mixture although the yield was too low to allow its isolation.