Divergent CH Insertion–Cyclization Cascades of N ‐Allyl Ynamides

Gold carbene reactivity patterns were accessed by ynamide insertion into a C(sp 3 )H bond. A substantial increase in molecular complexity occurred through the cascade polycyclization of N ‐allyl ynamides to form fused nitrogen‐heterocycle scaffolds. Exquisite selectivity was observed despite several competing pathways in an efficient gold‐catalyzed synthesis of densely functionalized C(sp 3 )‐rich polycycles and a copper‐catalyzed synthesis of fused pyridine derivatives. The respective gold–keteniminium and ketenimine activation pathways have been explored through a structure–reactivity study, and isotopic labeling identified turnover‐limiting CH bond‐cleavage in both processes.