Qualitative Analysis of the Stability of the Oxazine Ring of Various Benzoxazine and Pyridooxazine Derivatives with Proton Nuclear Magnetic Resonance Spectroscopy

A series of 3,4‐dihydro‐1,3‐benzoxazine and 3,4‐dihydro‐1,3‐pyridooxazine derivatives was synthesized, and the hydrolysis of the derivatives was studied with proton nuclear magnetic resonance spectroscopy. The oxazine derivatives underwent various degrees of hydrolysis when H2O was added to dimethyl sulfoxide solutions of the compounds. The rates and extents of decomposition of the oxazine ring systems depended on the electronic effects of substituents within the molecules. Examination of the proton nuclear magnetic resonance spectra that were generated during decomposition of the oxazines and trends in stability of the oxazine derivatives suggest the formation of an intermediate in the hydrolysis mechanism.