Nitrone cycloaddition: peracid oxidation of perhydro-1,2-oxazolo[3,2-c][1,4]oxazines

Regiochemistry of peracid induced ring opening of perhydro-1,2-oxazolo[3,2-c][1,4]oxazines (2) and (6) in aprotic solvent is dictated by orientation of lone pair of electrons on nitrogen. In contrast to the case with the corresponding hexahydro-2H-isoxazolo[2,3-a]pyridines (17), the oxidation of (2) gives mainly an equilibrium mixture of aldonitrone (3) and its hydroxylamine tautomer (4) which undergo stereoselective cycloaddition with styrene and methyl methacrylate. The X-ray diffraction study reveals the 6-5 ring system in (2) to be cis fused.