Alkyne is the most important precursor for vinyl radical generation, which is a versatile synthetic intermediate. The synthetic value of vinyl radical has been well revealed, especially in radical cascade and cyclization reactions. The vinyl radical chemistry has further blossomed recently by the development of photocatalysis in organic synthesis. Though significant development of beta-carbon, beta-sulfur, and beta-tin vinyl radicals mediated reactions have been achieved. Surprisingly, reactions and synthetic applications of beta-oxyvinyl radical, a synthetically highly attractive intermediate, are severely underdeveloped. Recently, our group first reported a novel photocatalytic strategy for the generation of reactive and controllable beta-oxypyridinium radical through mild visible-light photoredox catalyzed single-electron oxidation of an alkyne/pyridine N-oxide system. Accordingly, an acridinium photoredox catalyzed ortho-alkylation reaction of pyridine N-oxide with arylalkynes or ynamides was developed. Furthermore, by applying this strategy, we have developed the first photoinduced oxidative cyclopropanation of ene-ynamides, via beta-oxypyridinium vinyl radical cascades. The synthetic applications of this innovative strategy for b-oxypyridinium radical generation have been just initiated. Ongoing studies in our group include the photoredox catalyzed oxidative cyclization of general 1,n-enynes, homolytic aromatic substitution, and C(sp3)–H functionalization reactions. Our exploration of this strategy provides new access to the development of beta-oxyvinyl radical cascades for the synthesis of structurally sophisticated substrates under mild conditions. In addition to the “classical” vinyl radical cascade, new reactive models, such as enolate umpolung reactivity, are envisioned and could provide new opportunities for the discovery of attractive divergent synthetic methods.

Photoredox catalyzed beta-oxyvinyl radical generation from alkynes for organic synthesis

ACS Spring 2022

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