The oxidative cleavage of alkenes is an important transformation in organic synthesis which converts alkenes into aldehydes, ketones or carboxylic acids. The two most common methods for this transformation are ozonolysis and the Lemieux-Johnson reaction. However, despite their usefulness, both of them have major issues associated with them. A new photochemical method which uses bench-stable and economical nitroarenes as oxygen transfer reagents was introduced independently by Ruffoni et al. [Nature 2022, 610 (7930), 81-86] and Wise et al. [J. Am. Chem. Soc. 2022, 144 (34), 15437-15442] in 2022. Their method exhibits good chemical yields, a large scope and high selectivity, while avoiding the use of precious metals and the formation of explosive intermediates. Despite the great relevance of this reaction heretofore no investigation of the mechanism of the initial photoaddition has been undertaken.
To fill this gap, researchers at HHU Düsseldorf (Gilch group) have teamed up with the Bredenbeck (Frankfurt University) and Dreuw (Heidelberg University) groups. Employing steady state and femtosecond UV/Vis and IR spectroscopy as well as quantum chemistry, kinetics and mechanism for a representative nitroarene / alkene pair were elucidated. Their results show that, for typical alkene concentrations, reaction quantum yields amount to only a few percent. Time resolved spectroscopy attributes this low efficiency to the short triplet lifetime of the nitrobenzene derivative and the unreactive decay of an intermediate on the path to the dioxazolidine adduct. Clear-cut evidence for the triplet biradical nature of this intermediate is given. Thus, a full picture of the reaction mechanism is established. With this comprehensive knowledge a targeted improvement of the efficiency should be possible
Original publication
Klaverkamp, D.; Schneider, F.; Denninger, L.; Rach, L.; Bredenbeck, J.; Dreuw, A.; Gilch, P. Molecular Mechanism of the Oxidative Cleavage of Alkenes by Photoexcited Nitroarenes. J. Am. Chem. Soc. 2026, 148, (22), 22488–22503