Over the past decade, the development of photocatalysis in organic synthesis has enabled the invention of new activation modes for organic substrates and delivered a wide variety of nontraditional bond-forming protocols and synthetic methodologies. However, the achievement of alkyne single-electron oxidation and its application in synthetically meaningful organic transformations has yet to be accomplished in a catalytic manner. In this regard, we recently developed a novel and facile access to the cationic enol radical through photocatalyzed alkyne activation by pyridine N-oxide. Accordingly, a photocatalyzed ortho-alkylation of pyridine N-oxide with ynamides and arylacetylenes has been developed, yielding a series of α-(2-pyridinyl) benzyl amides/ketones. As our continuous effort to extend the synthetic applications of this strategy, we now report a series of photocatalytic intramolecular cycloaddition reactions of ynamides. This research provides a general and metal-free methodology for the efficient synthesis of densely functionalized and biologically relevant heterocyclic compounds, including aza-bicyclohexan-2-ones, pyrrolidin-2-ones, and 1,4-oxazepan-5-ones.

Photocatalytic synthesis of heterocyclic compounds through a cationic enol radical from ynamide and pyridine N-oxide

ACS Fall 2020 Virtual Meeting

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