Pyridine N-Oxide derivatives have been well documented as electro-pair donors, mild oxidants, and ligands in metal complexes in two-electron chemistry as well as their abilities as electron donors or acceptors in single-electron chemistry. What hasn’t been studied as in-depth is the utilization of a pyridine N-Oxide’s single electron chemistry to develop an N-oxide cation radical in radical chemistry and synthesis.
In this research, a photocatalytic strategy was developed to develop vinyl radicals through photoinduced single-electron oxidation of pyridine N-oxides/alkyne systems. Additionally, ortho-alkylation of pyridine N-oxide and photocatalyzed cyclopropanation were also observed. In a possible mechanistic pathway, pyridine N-oxide cation radicals are generated from single-electron oxidation of pyridine N-oxides by acridinium photoredox catalyze and react with alkynes to generate a β-oxypyridinium vinyl radical intermediate. From these results, it’s proposed a highly electrophilic pyridine N-oxide could act as a HAT mediator to remove a hydrogen atom from a carbon-hydrogen bond to develop a carbon radical, subsequently leading to its functionalization.
To test this proposed method, a series of commercial pyridine N-oxides derivatives were used as HAT catalyst in the photoinduced catalyzed carbon-hydrogen alkylation of cyclooctane with benzalmalononitrile. A 9-mesityl acridinium photocatalyst could promote a single-electron oxidation of pyridine N-oxides.
It was found that the presence of the photocatalyst under blue LEDs with 2,6-dichloropyridine N-oxide showed to be the most effective HAT catalyst.

Jujhar Singh

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