Divergent Synthesis of Polycyclic N‑Heterocycles via Controllable Cyclization of Divinylallenes Catalyzed by Copper and Gold.

The generation of metal carbenes from readily available allenes represents a remarkable advance in metal carbene chemistry. However, most of these transformations are mainly restricted to the noble-metal catalysts (Au and Pt). Here, a copper-catalyzed desymmetric cyclization reaction of divinylallenes is described, enabling the practical and atom-economical synthesis of a diverse array of valuable triazolo-fused pyridazines and tetracyclic N-heterocycles by a presumable copper carbene intermediate and a highly selective 1,2-N shift process. In contrast to copper catalysis, tricyclic N-heterocycles are formed exclusively under gold catalysis via a presumable 1,2-H-migration. Catalyst-controlled migration is achieved by effective catalyst-controlled site selectivity. In addition, in the presence of oxidant, the copper-catalyzed desymmetric oxidation reaction affords the divergent formation of cyclopentanone-fused tricyclic heterocycles in a one-pot process, where no 1,2-migration into the copper carbenes is observed. Importantly, the mechanistic rationale for this allene cyclization, in particular, accounting for the distinct migration into metal carbenes, is also strongly supported by theoretical calculations.