Synthesis of Pyrrolidines and Pyrrolizidines with α‐Pseudoquaternary Centers by Copper‐Catalyzed Condensation of α‐Diazodicarbonyl Compounds and Aryl γ‐Lactams

N‐aryl γ‐lactams react intermolecularly with acceptor–acceptor diazo reagents, usually dicarbonyl compounds, in a copper‐catalyzed process to yield functionalized pyrrolidines with α‐pseudoquaternary centers. As 1,2‐acyl or ‐phosphoryl migration is preferred, single regioisomers are obtained. Furthermore, in the presence of a Lewis acid, subsequent Friedel–Crafts reactions yield tricyclic pyrrolizidines in excellent yields (90–96 %) and diastereoselectivities (up to >20:1).