Highly <i>trans-</i>Stereoselective Synthesis of Bicyclic Isoxazolidines via Copper-Catalyzed Triple Cascade Catalysis

A triple cascade was developed using a simple copper catalyst to trans-selectively access bicyclic isoxazolidines in a one-pot synthesis. This strategy features the in situ generation of nitrones and subsequent trapping by [3 + 2] cycloaddition. In this method, copper serves three catalytic functions: as a Lewis acid for the ene reaction, as an organometallic for aerobic oxidation, and as a Lewis acid for an endo-selective [3 + 2] cycloaddition. The successful merging of aerobic oxidation and Lewis acid catalysis demonstrated efficient cascade synergy.