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Photochemical oxidation of helical amines

Helically chiral aromates called helicenes are at the centre of attention of the scientists from our institute.  Research is primarily focused on applications of these molecules in material science. The team lead by dr. Storch and dr. Sýkora have recently disclosed an effective method of functionalization of the helicene structure by visible light, which was published in prestigious scientific journal focusing on organic chemistry, Organic Letters. The published method uses easily available aminohelicenes for their oxidation by aerial oxygen into valuable ortho-diketones. These compounds can be used as a versatile intermediate for introduction of a plethora of functional features and a modification of the physical properties of the helicene moiety according to requirements of a given application. The charm of the chemical transformation consist of high reaction yields of both steps without any side products. Beside other things, the article describes the influence of both the structure of the starting aminohelicenes and wavelengths of the visible light used for the transformation. Very unusual selectivity of this transformation for non-planar aromates was discovered. Furthermore, the mechanism of the reaction was described in detail. Firstly, aminohelicene photosensitizes the formation of singlet oxygen, which then undergoes [2+2]-photocycloaddition with the enamine double bond of the aminohelicene. The formed 1,2-dioxetane is then decomposed to the product, water and ammonia. The aminohelicene has three different functions in the reaction mechanism – aside from being the reactant, it also functions as a photosensitizer and a base, which are both crucial for the reaction. This method can greatly facilitate the development of specialized materials for optoelectronics.

Jakubec, M., Hansen-Troøyen, S., Císařová, I., Sýkora, J., Storch, J. Photochemical Oxidation Specific to Distorted Aromatic Amines Providing ortho-Diketones. Organic Letters. 2020, 22, 10, 3905–3910, . ISSN 1523-7060. 
DOI: 10.1021/acs.orglett.0c01190


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