Diastereoselective [2,3]-sigmatropic rearrangements of lithium N-benzyl-O-allylhydroxylamides bearing a stereogenic centre adjacent to the migration terminus

The diastereoselective [2,3]-sigmatropic rearrangements of lithium N-benzyl-O-allylhydroxylamides bearing a stereogenic centre adjacent to the migration terminus are examined. (E)-N-Benzyl-O-(4-phenylpent-2-enyl)hydroxylamine rearranges in 30% de to afford syn-(3RS,4RS)-3-(N-benzyl-N-hydroxy)-4-phenylpent-1-ene as the major diastereoisomer, consistent with the rearrangement proceeding under moderate steric control. Rearrangements of both lithium (E)- and (Z)-N-benzyl-O-(4-methoxy-4-phenylbut-2-enyl)hydroxylamides furnish syn-(1RS,2RS)-1-phenyl-1-methoxy-3-(N-benzylamino)but-3-ene in ≥90% and 88% de respectively, consistent with these rearrangements proceeding under chelation control.