Diastereoselective synthesis of cis-2,5-disubstituted pyrrolidine N-oxides by the retro-Cope elimination

Nitrones were reacted with 3-butenylmagnesium bromide to give alkenylhydroxylamines that were cyclised by retro-Cope elimination. Heating the diastereomeric mixtures of pyrrolidine N-oxides in the absence of solvent affected a highly diastereoselective isomerisation to provide the cis-2,5-disubstituted products in excellent yield.