N-methylhydroxylamine hydrochloride in boiling ethanol-pyridine (1:1) solution results in elimination of the CH3NH2fragment, affording products of oxidative hydrolysis 4a, 4b, and 6b, while acid-catalyzed reaction of isoxazolidines 2a, 3a and 5b leads to rearrangement involving the N-CH3 group with formation of the perhydro-3,1-oxazine derivatives 8a, 9a and 10b.