A novel copper-catalyzed tandem cyclization/direct C-(sp 2 )−H annulation of phenyl azide−ynamides via α-imino copper carbenes has been developed, which provides a concise and flexible approach for the construction of a range of valuable azepino[2,3-b:4,5-b′]diindoles in mostly good to excellent yields with high chemoselectivities. This tandem reaction also exhibits a broad substrate scope, excellent functional group tolerance, simple operation, and mild reaction conditions.

Over the past two decades, catalytic alkyne alkoxylation-initiated Claisen rearrangement has proven to be a practical and powerful strategy for the rapid assembly of a diverse range of structurally complex molecules. The rapid development of Claisen rearrangements triggered by transition-metal-catalyzed alkyne alkoxylation has shown great potential in the formation of carbon–carbon bonds in an atom-economic and mild way. However, metal-free alkyne alkoxylation-triggered Claisen rearrangement has seldom been exploited. Recently, Brønsted acids such as HNTf2 and HOTf have been shown to be powerful activators that promote catalytic alkyne alkoxylation/Claisen rearrangement, leading to the concise and flexible synthesis of valuable compounds with high efficiency and atom economy. Recent advances on the Brønsted acid catalyzed alkyne alkoxylation/Claisen rearrangement are introduced in this Account, in which both intramolecular and intermolecular tandem reactions are discussed.