3-alkyl-substituted 1,2-oxazine N-oxides 2 can be selectively transformed into 2-silyloxy-1,2-oxazines 1 upon treatment with silylating reagents. In the solid state derivatives 1 adopt a chair conformation with the pyramidal nitrogen atom, whereas in solution they exist as an equilibrating mixture of two conformers (DeltaG++ 55-60 kJ/mol). A preliminary study of the reactivity of nitrosals 1 has shown that they react with O- and N-stabilized carbocations to yield 1,2-oxazine N-oxides with a functionalized alkyl substituent at the 3-position. Moreover, compounds 1 can rearrange into silyloxy-1,2-oxazines 5 and react with morpholine to produce 3-morpholinoalkyl-1,2-oxazines 7 existing in a tautameric equilibrium with open-chain oximes 6.
A number of 3-bromo-5,6-dihydro-4H-1,2-oxazine Noxides have been synthesized and subjected to [3+2] cycloaddition with alkenes affording various types of products: 3-vinyloxazolines, isoxazoline N-oxides, and 3-functionalized 1,2-oxazine N-oxides.
A Convenient Procedure for the Synthesis of Substituted 3-α-Haloalkyl-5,6-dihydro-4H-1,2-oxazines. -The title compounds are directly obtained from cyclic nitronates and trimethylsilyl halides. The latter [cf. (VI)] can be readily subjected to nucleophilic substitution reactions with cyanide or malonate. Interestingly, under milder reaction conditions the intermediate enamines (IV) and (VII) can be isolated in excellent yields. -(KLENOV, M. S.; LESIV*, A. V.; KHOMUTOVA, Y. A.; NESTEROV,
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