Cyclic nitronic esters from highly diastereoselective cycloaddition of 2-(4-morpholinyl)norbornene to conjugated nitroolefins

Abstract

The reactions of the morpholino enamine of 2-norbornanone towards a series of cyclic and acyclic conjugated nitroolefins resulted in the formation of the corresponding 1,2-oxazine N-oxides through an exo approach of the electrophiles. The stability of the heterocycles was strongly influenced by the nature of the substituents and in some cases it has been found to be unexpectedly high. Differently from analogous systems, opening of the heterocyclic ring to the corresponding enamine systems was not observed.