Development of efficient and selective methods for carbon-carbon and carbon-heteroatom bond formation has been a standing goal of organic synthesis. 1,3-Dipolar cycloaddition reactions are powerful tools to synthesize 5-membered heterocycles with a broad range of carbon-heteroatom bonds from structurally diverse dipoles and dipolarophiles. Here, we present a novel reaction between lithium acetylides and N-sulfonyl azides that proceeds via a cascade of transformations. In this process, a diazoalkene species is generated in situ that undergoes an intramolecular 1,3-dipolar cycloaddition with an aromatic group, a ubiquitous moiety yet an unexplored dipolarophile. The reaction generates densely functionalized annulated sultam-indazole intermediates which can be further converted to stable organic scaffolds. The involvement of aromatic groups in the 1,3-dipolar cycloadditions broadens the utility of the diazoalkenes, a family of dipoles that are barely studied and difficult to access.

Overcoming the constraints of aromaticity: Unexpected reactivity of alkynes and N-sulfonyl azides in 1,3-dipolar cycloaddition

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