Rh(III)-Catalyzed Cascade Annulation to Produce N-acetyl Chain of Spiropyrroloisoquinoline Derivatives

Rhodium(III)-Catalyzed Redox-Neutral [4 + 2] Annulation of 3,5-Diaryloxadiazoles with Alkynes: A Dual C-H Activation Strategy for Constructing C-N Atropisomers

A rhodium(III)-catalyzed dual-ring formation via cascade C-H activation/[4 + 2] annulation of 3,5-diaryoxadiazoles with alkynes was developed. This strategy has been demonstrated with a variety of 3,5-diaryloxadiazoles and alkynes, and it has been successfully scaled up to gram-scale synthesis, highlighting its potential significance in the direct construction of C-N atropisomers. Furthermore, the cleavage of the N-O bond is essential for the formation of the bicyclic structure in the absence of an external oxidant. Mechanistic studies revealed that cleavage of the C-H bond at the 3-phenyl group of oxadiazole was likely a rate-determining step in this reaction.

Rh(III)-Catalyzed Double Annulation of 3-Phenyl-1,2,4-oxadiazoles with 2-Diazo-1,3-diketones: Access to Pyran-Fused Isoquinolines

Efficient access to pyranoisoquinoline derivatives via rhodium-catalyzed double C-H functionalization of phenyl oxadiazoles and diazo compounds has been developed. Two C-C bonds and one C-O and C-N bond formation was realized by this tandem reaction, along with the formation of two heterocycles, affording diversified pyran-fused isoquinolines in moderate to good yields with broad functional group tolerance under mild reaction conditions.

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.