Diastereoselective Construction of Fused Carbocyclic Pyrrolidines via a Copper-Catalyzed [3 + 2] Cycloaddition: Total Syntheses of Pancratinines B–C

A Cu-catalyzed diastereoselective [3 + 2] cycloaddition of 2-arylaziridines and cyclic silyl dienol ethers was developed to efficiently construct fused-[5,n] carbocyclic pyrrolidines, which are widespread in bioactive natural products. Mechanistic studies revealed that the high diastereoselectivity of this transformation arose from a sequential retro aza-Michael/epimerization/aza-Michael process. Taking advantage of this newly developed method, the first total syntheses of pancratinines B and C were concisely realized.