Photophysical Properties and DFT Study of Substituted Benzo[b][1,4]Oxazepine Derivatives by the Reaction of 2‐Aminophenols With Ethyl‐2‐Cyano‐3,3‐ bis Methylthio Acrylate

We have synthesized 4‐(methylthio)‐2‐oxo‐2,5‐dihydrobenzo[b]oxazepine‐3‐carbonitrile and its derivatives, which represent a rare class of benzoxazepine derivatives. These derivatives were synthesized by reacting 2‐aminophenols with ethyl‐2‐cyano‐3,3‐bis(methylthio)acrylate at 120 °C in the presence of potassium carbonate (K 2 CO 3 ) as a weak base and dimethylformamide (DMF) as a solvent. A number of benzo[b]oxazepine derivatives can be obtained using the synthetic method presented here. Based on mechanistic studies, we observed that the hydroxy proton of the aminophenol may be essential for the formation of an intermediate methylthio amide that undergoes 7‐endo‐dig cyclisation, to understand the quantum efficiencies of the new benzo[b]oxazepine derivatives, their photophysical properties were examined using absorption and emission spectroscopy. The mechanistic explanation is further supported by DFT analysis of the HOMO and LUMO energy levels.