Enantioselective Staudinger Synthesis of β-Lactams Catalyzed by a Planar-Chiral Nucleophile

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Abstract
The development of efficient methods for the stereoselective generation of β-lactams is an important goal, due to their biological activity and their utility as synthetic intermediates. The Staudinger reaction, an overall [2 + 2] cycloaddition of a ketene with an imine, provides a nicely convergent route to this family of compounds. Nearly all studies to date of asymmetric variants of the Staudinger reaction have focused on the use of chiral auxiliaries to control the stereochemistry of the β-lactam. In this report, we establish that a planar-chiral derivative of 4-(pyrrolidino)pyridine serves as a very effective enantioselective catalyst for the Staudinger β-lactam synthesis, coupling a range of symmetrical and unsymmetrical ketenes with an array of imines with very good stereoselection and yield.