The general procedure for the synthesis of 1,2-oxazinoline hydrochloride from the compound (CAS:664364-75-4) was as follows: 21a-2 (55 g, 0.29 mol) was dissolved in tert-butyl methyl ether (TBME, 80 mL) at room temperature. Subsequently, a TBME solution (600 mL) of 4N HCl was slowly added to this solution. The reaction mixture was stirred continuously for 3 hours at room temperature. Upon completion of the reaction, the precipitated solid was collected by filtration and washed with TBME (50 mL), resulting in 21a-3 (30 g) as a white solid.
