Cu(I)/Bis(azaferrocene)-Catalyzed Enantioselective Synthesis of β-Lactams via Couplings of Alkynes with Nitrones

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Abstract
As a consequence of the wide-ranging significance of β-lactams (e.g., use as drugs and as chiral building blocks), a great deal of effort has been dedicated to the development of methods for their stereoselective synthesis. Although considerable progress has been achieved, nearly all of the approaches that have been described are based on the use of chiral precursors; direct catalytic enantioselective routes to β-lactams are rare as well as limited in scope. In this communication, we establish that, using a new C2-symmetric planar-chiral bis(azaferrocene) ligand, we can generate β-lactams with very good enantiomeric excess and cis diastereoselection via catalytic enantioselective Kinugasa reactions (couplings of alkynes with nitrones). Appealing attributes of this process include the ready availability of the starting materials, the functional-group tolerance of the reaction, and the convergency of the approach.