Preparation of highly substituted 7-oxa-1-azabicyclo[2.2.1]heptanes from 4-nitro-1-butene derivatives. Route to polysubstituted piperidines

4-Nitro-1-butene derivatives 2 readily available from the palladium(0)-catalyzed C-allylation of nitroalkanes were converted into highly substituted 7-oxa-1-azabicyclo[2.2.1]heptane derivatives 6 in three steps including an intramolecular 1,3-dipolar cycloaddition reaction. Catalytic hydrogenolysis of the N–O bond in 6 afforded polysubstituted 4-hydroxypiperidines.