α-Halonitriles are common intermediates in organic synthesis due to their utilization as masked ketones. Typical procedures for revealing ketones from α-chloronitriles require harsh conditions such as concentrated base or Na2S at elevated temperatures, which lack functional group compatibility, especially in complex settings. During the course of our studies on the reactivity of bis(1-halomucononitriles), we found that the aforementioned strategies are ineffective for the conversion of α-bromonitriles to ketones and thus the development of an alternative hydration approach is necessary. We report a two-step procedure to convert α-bromonitriles to ketones employing radical trapping by (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) followed by zinc mediated N—O bond cleavage. The trapping reaction proceeds smoothly in the presence of the photoredox catalyst fac-Ir(ppy)3 under 427 nm or 390 nm irradiation with α-TEMPO nitrile adducts isolated in 61-98% yield. With 427 nm light, excitation of the catalyst followed by single electron reduction of the substrate predominates, while 390 nm light promotes a considerable background C—Br bond homolysis leading to TEMPO trapping. The α-TEMPO nitrile adducts were also manipulated to afford TEMPO-containing compounds with carbonyl and amine functionality. The development of this method has enabled the synthesis of a variety of ketones previously inaccessible using traditional strategies.

Photooxygenation of α-bromonitriles using TEMPO as an O-atom transfer reagent

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