IMPHOCHEM

The IMPHOCHEM project deals with photochemical transformations of cyclic imines, which is based on a multidisciplinary approach combining organic synthesis, theoretical chemistry and chemical engineering. In this reactions, after photochemical excitation, an intramolecular hydrogen transfer occurs from the hydrogen donor moiety to the electronically excited imine function, involving thus a C H activation without a chemical regent. In the context of the project, two principal mechanisms are discussed: the hydrogen atom is transferred in one-step process (the proton and the electron are simultaneously transferred) or a two-step process takes place (the electron is transferred first and the proton follows). Depending on the hydrogen donor and the substitution of the imine, one of these mechanisms is preferred. After radical combination, a C C or a C N bond is formed. Different stereoisomers are formed. Particular attention is paid to the influence of the mechanism and the temperature on the stereo and regioselectivity. Theoretical methods are used in order to determine the properties of the excited state (spin density, electron distribution) and to study conformational equilibria. In the case of a two-step mechanism of hydrogen transfer involving photochemical electron transfer, photoredox catalysis (with visible light) is possible. Corresponding reaction conditions will be tested. In order to determine scope and limitation of the reaction, the substitution of the imine and the nature of the hydrogen donor will be broadly varied. Natural product derived structures (for example: carbohydrates, alkaloids or steroids) will also be attached as hydrogen donor. These variations will lead to an original molecular complexity and a high molecular diversity. A certain number of particularly efficient and original reactions will be selected in order to prove their usefulness for application to organic synthesis, more precisely for the synthesis of biologically active compounds. The study of photochemical transformations under flux conditions is a further original point of the project. A LED-driven microreactor operating in the UV-B domain (below 300 nm) and under temperature-controlled condition will be used. The conception and construction of such a reactor is particularly challenging and will open numerous perspectives in the field of flow photochemistry. Using such a reactor in this project will also help to understand fundamental aspects on how the selectivity depends on the temperature and the irradiation. By combining specific experiments with the modeling tools of photochemical reactor engineering, it will be possible to define the optimal operating conditions and to evaluate the feasibility of a transposition to a larger scale.