Synthesis and study of 3-allyl and 3-methallyl quinazolin-4(3H)-one by gas chromatography-mass spectrometry

3-Allylquinazolin-4( 3H )-one (2a) and 3-(2-methyl-2-propen-1-yl)quinazolin-4( 3H )-one (2b) were synthesized by the interaction between quinazolin-4( 3H )-one and allyl (methallyl) halide in the presence of potassium carbonate and dimethylformamide (DMF) or in the presence of potassium hydroxide and propan-2-ol. The 1H NMR spectra of the obtained compounds have signals of protons of the allyl (methallyl) group. The proton signals of the -NCH2 group for compounds 2a,b are located at 4.63 and 4.58 ppm. The IR spectra of the synthesized compounds have absorption bands of the carbonyl group in the range 1650-1660 cm-1. This proves that the reaction proceeds through the nitrogen atom. The main mass fragmentation paths for N-derivatives of quinazolin-4( 3H )-one have been revealed by gas chromatography-mass spectrometry analysis. The mass spectra of compounds 2a,b contain the molecular ion peak. For compound 2a it is 63 %, and for 2b it is 18 %. The maximum for both compounds is the [M-CH3]+peak. Probably the formation of this peak is due to the fact that the elimination of methyl radical produces aromatic oxazolo[ 3,2-c ]quinazoline systems. The formation of the [M-H]+peak is explained by the formation of aromatic cation of oxazolo[ 3,2-c ]quinazoline system. The peak intensity for 2a is 56 %, for 2b it is 41 %. The spectra of both compounds contain peaks of the [M-OH]+ fragment, whose intensity is 20-25 %. In our opinion, the isomerization proceeds with formation of the 4-hydroxy-3-(2-methylpropenyl)quinazoline cation radical, which forms the stable 1H-pyrrolo[ 3,2-c ]quinazoline cation after detachment of hydroxyl radical. In the mass spectra of compounds 2a,b there are [M-CO]+peaks, which are typical for hexatomic ketones. Nevertheless, they have a low intensity: for 2a the peak intensity is 3 %, and for 2b it equals 1 % only. The spectra of compounds 2a, b show the peak with m/z = 145, which corresponds to detachment of the allyl (methallyl) radical and formation of the quinazolone-4( 3H )-one cation. The presence of the peak with m/z 146 is due to formation of cation radical of the original quinazoline as a result of the allene detachment. In the mass spectra of both compounds there is the peak of allyl cation ( m/z = 41) and methallyl cation ( m/z = 55), respectively.