Ring-Opening/Ring-Closing Protocols from Nitrothiophenes: Easy Access toN-Fused Pyrroles through a Tandem 1,6-H Shift/6?-Electrocyclization

The unusual migration of a nitro group from the β- to the α-position of a β-aryl-α-nitroethenyl moiety, following a nitrocyclopropane to isoxazoline N-oxide isomerization, has been studied from a mechanistic and synthetic points of view. As a result, two series of isomeric isoxazoline N-oxides could be obtained under controlled conditions. When reacted with diazomethane, a model transposed isoxazoline cleanly furnished a new, interesting pyrazolylisoxazole.