N-Nitrosodehydromorpholine, a potential metabolic intermediate in the
carcinogenic activation of N-nitrosodiethanolamine, and N-nitrosomorph
oline, was prepared from the hemiacetal N-nitroso-2-hydroxymorpholine
(2) by tosylation and in situ base-catalyzed elimination. The attempte
d acid-catalyzed hydration of 3 gives neither 2 nor the unstable alpha
-hydroxynitrosamine, N-nitroso-3-hydroxymorpholine (4). The product of
this transformation is N-(2-hydroxyethyl)-2-oximinoethanamide (5) as
confirmed by an X-ray crystallographic determination. Treatment of 3 w
ith gaseous HCl in CH2Cl2 gives 1-aza-4-oxa-3-oximinocyclohexene (6),
which rearranges to 5 upon treatment with aqueous acid. The initial re
arrangement was proven to be intermolecular by means of a crossover ex
periment employing (NO)-N-15 and C-5-D-2 isotopomers of 3.