[4+2]-cycloadditions of thiones with nitrosoalkenes: synthesis of derivatives of 4H-1,5,2-oxathiazine, a new heterocyclic system.

Conjugated nitrosoalkenes, generated in situ via dehydrobromination of α-bromoketoximes, undergo an easy [4+2]-cycloaddition with thiocarbonyl compounds to give very high yields of the new heterocycles 4H-1,5,2-oxathiazines. The thermolysis and the behaviour to oxidation of these adducts were tested.