Synthesis of 1,2-oxazine N-oxides via noncatalyzed hetero-Diels–Alder reactions of nitroalkenes (microreview)

In this microreview, the application of noncatalyzed hetero-Diels–Alder reaction (formally [4+2] cycloaddition) with participation of conjugated nitroalkenes and their analogs for easy and selective preparation of 1,2-oxazine N-oxides was reviewed on the basis of recent publications. It was found that the best described processes are realized with full regioselectivity as well as at mild temperatures. It is interesting, that in some cases of the title reactions, the stepwise mechanism of the formation of the six-membered heterocyclic ring is more possible than classic one-step mechanism.