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 a 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.