General Asymmetric Synthesis of Densely Functionalized Pyrrolidines via Endo-Selective [3+2] Cycloaddition of β-Quaternary-Substituted Nitroalkenes and Azomethine Ylides.

A scalable endo-selective synthesis of 2,3,4,5-tetrasubstituted pyrrolidines via cycloaddition of nitroalkenes and azomethine ylides is reported using a P,N-type ferrocenyl ligand and [Cu(OTf)]2·C6H6. The robust method is tolerant of a wide range of functionalities, including rarely reported quaternary nitroalkene substitution and heteroaromatic and hindered ortho-substituted arenes on the azomethine ylide. Subsequent transformations highlight the utility of the method in the synthesis of densely functionalized small molecules suitable for fragment-based drug discovery and the cystic fibrosis C2-corrector clinical candidate ABBV-3221.