Highly Diastereoselective Allylic Azide Formation and Isomerization. Synthesis of 3(2'-Amino)-beta-lactams

The stereoselective anti SN2’ attack of NaN3 to 3-alkenyl-3-bromo-azetidin-2-ones gave a mixture of diastereomeric azides in fast equilibrium. The [3,3]-sigmatropic rearrangement of allylic azides occurred with complete stereocontrol allowing the equilibrium to be directed preferentially towards the (E) or (Z) isomer, useful precursors of 3(2’-amino)-beta-lactams