Construction of Rings via Metal-Catalyzed C-H Annulation with Unsymmetrical Internal Alkynes: Selectivity and Applications

Selective and concise construction of ring systems that are ubiquitous skeletons across chemistry, drugs and materials, is indispensable for human life. Of note, directed C-H annulation with alkynes for the expedient delivery of ring systems holds great importance, featuring step- and atom-economy, mild conditions, and broad substrate scope. However, regioselectivity issues remained when using unsymmetrical alkynes for the directed C-H annulation. Herein, we summarized recent achievements towards solving this problem by developing directing groups, metal catalysts, and alkynes with versatile and traceless functionality that ensure the overall regioselectivity, enantioselectivity, efficiency, and synthetic application. We hope this concept will promote the further development of the precise construction of functional molecules using C-H annulation with unsymmetrical alkynes. C-H annulation with alkynes has been demonstrated to be one powerful strategy for the expedient construction of ring systems, while the use of unsymmetrical alkynes often led to elusive regioselectivity. Herein, we summarized recent exploration of this field, including the development of directing groups, catalytic systems, and versatile alkynes, which has led to prosperous achievements toward the application in drugs, natural products, and materials.+image