Synthesis, IR spectral studies and quantum-chemical calculations on 1,2-dihydronaphto[1,2-e]oxazine-3-thiones and 3,4-dihydrobenzo[e][1,3]oxazine-2-thione

2-Hydroxy-1-naphthaldehyde (1) was reacted with substituted anilines to afford 1-(substituted phenyliminomethyl)naphthalen)-2-ols (2). The reduction of these imines by NaBH4 gave 1-((substituted phenylaminomethyl)naphthalen)-2-ols (3) which were cyclized with thiophosgene to give corresponding 2-substituted phenyl-1,2-dihydronaphto[1,2-e]oxazine-3-thiones (4). 3-p-Tolyl-3,4-dihydrobenzo[e][1,3]oxazine-2-thione (8) was also obtained by the same way. The structures of these new compounds were determined by 1H NMR, IR spectroscopic data and elemental analyses. AM1, PM3 and ab initio (at Hartree–Fock level with 3-21G basis set) methods were used to study the molecular geometry of the compounds. A complete infrared spectral analysis of the oxazines has been performed in this paper. Observed frequencies of the molecules were compared with calculated normal mode analysis which was carried out on the basis of RHF/3-21G method. Assignments of vibrational bands (in the range of 1760–400 cm−1) have been performed by taking into account the results of the ab initio vibrational analysis. The mechanism of the cyclization reaction between (3a) and thiophosgene was studied by the semi-empirical AM1 and ab initio (RHF) calculations.