C–H activation-initiated spiroannulation reactions and their applications in the synthesis of spirocyclic compounds

Spirocyclic skeletons are prevalent in natural products, pharmaceuticals and organic functional materials. Meanwhile, transition-metal-catalyzed C-H activation reactions have demonstrated unparalleled advantages such as high efficiency, excellent atom-economy, good chemoselectivity and regioselectivity for the formation of target organic molecules. In recent years, C-H activation reactions have been creatively utilized in the synthesis of spirocyclic compounds. This review summarizes the most recent progress made in C-H activation-initiated spiroannulation reactions and their applications in the construction of structurally diverse and biologically valuable spirocyclic scaffolds by using alkynes, diazo compounds, maleimides, alkenes, quinones and cyclopropenones as the coupling partners.