AbstractThe hydrolytic decomposition of 2‐phenyl‐ and 2‐isopropyl‐3‐methyltetrahydro‐1,3‐oxazines to 3‐methylaminopropan‐1‐ol and appropriate aldehydes was studied by1H NMR and UV spectroscopy in acidic solutions. The time‐dependent spectra confirmed that the formation of the final products was preceded by an equilibration of three components, the two Schiff base intermediates and the starting material, of which the former produced a carbinolamine which in turn underwent heterolysis