The formation of radicals and radical cations result from oxidative processes. When oxidation of oximes and oxime ethers occur, iminoxyl radicals and oxime radicals are produced. The reactivity of these intermediates is largely unexplored and to learn about the fundamental reactivity of iminoxyl radicals and oxime ether radical cations, we have begun an investigation on intramolecular reactions of oximes and oxime ethers using built-in alkenes as a potential nucleophile or radical trap. Previously, built-in alkynes were found to act as radical traps whereas aromatic rings were found to act as nucleophiles. This project explores the reactivity of alkene functional groups under similar oxidative conditions. We hypothesize that the alkene functional group may act as a nucleophile and as a radical trap to form the cyclized product. Photolysis of the substrate at 420 nm with 9,10-dicyanoanthracene (DCA) as the photosensitizer leads to the formation of the iminoxyl radical (oxime) or radical cation (oxime ether) intermediate that can then cyclize. Studies on the PET reactions of the vinyl oxime (1a) and oxime ether (1b) did not show any evidence of cyclization. Preliminary results suggest that cyclization occurs at the nitrogen for the 2-isopropenyl derivative for both the oxime (2a) and the oxime ether (2b). NMR analysis of both reactions upon irradiation at 420 nm in the presence of DCA for up to 4 hours shows the formation of new products over time; the product mixtures of the oxime and oxime ether show very distinct similarities suggesting that the products formed are very similar. The NMR results are consistent with structures formed using a cyclization pathway. The exact identity of the cyclic product formed in these reactions is unclear and further analysis of the reaction mixtures is being completed using NMR and GC/MS. Computational studies are being performed to obtain mechanistic insights into why the presence or absence of a methyl group on the alkene group has such a pronounced impact on the reaction. The results of these studies, as well as those of the E- and Z-propenyl derivatives (3a, 3b, 4a, and 4b) will be discussed.

Intramolecular oxidative cyclization reactions of oximes and oxime ethers using alkenes as a potential nucleophiles or radical traps

253rd National Meeting (2017)

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