Broadening the Synthetic Scope of the Iron(III)‐Catalyzed Aza‐Prins Cyclization

The nature and influence of the N ‐sulfonyl group in aza‐Prins cyclization and the reactivity of the six‐membered aza‐cycle generated has been studied. The aza‐Prins cyclization of γ,δ‐unsaturated amines with a tosyl group at the nitrogen atom produces 2‐alkyl‐4‐halo‐1‐tosyl‐1,2,5,6‐tetrahydropyridines with a halovinyl function, extraordinarily stable to further derivatization and detosylation conditions. To modulate the reactivity of such aza‐cycles, a general study of the aza‐Prins cyclization reaction was performed with several sulfonamides. Ring formation occurs satisfactorily with both N ‐nosyl and N ‐mesylamines providing optimal conditions for further synthetic transformations. To exemplify the scope of this methodology, a short synthesis of the alkaloid coniine was successfully carried out.