Alkenyl nitrones cyclizations induced by phenylselenenyl bromide. A convenient synthetic route to 1,2-oxazines

Abstract

Alkenyl nitrones reacted with phenyselenenyl bromide to afford ring closure reaction products deriving by the intramolecular capture of the seleniranium intermediates by the oxygen atom. Owing to the relative positions of the oxygen atom and of the carbon-carbon double bond in the nitrones employed, six-membered cyclic iminium salts were thus formed. These have ben directly treated with nucleophilic reagents and afforded 1,2-oxazine derivatives in good yield. It has been observed that, under the experimental conditions employed, the iminium salts in which the carbon-nitrogen double bond is exocyclic, depending on the nucleophile employed, gave the N-alkyl 1,2-oxazines and/or the N-unsubstituted 1,2-oxazines. On the contrary, with iminium salts in which the carbon-nitrogen double bond is endocyclic only N-alkyl 1,2-oxazines were obtained.