Photochemistry of Imines: Photoinduced Radical Reactions of imines
Investigation of photochemcial reactions of imines (mechanistic investigations, stereochemistry, application to organic synthesis) <br /> <br />Design and the building of a new in-house microphotoreactor operating in this UV-B domain. Performing and optimization of photochemical reactions of imines in this reactor.
A large variety of cyclic imines possessing an oxazolone moiety is synthesized. In almost all cases, the desired photochemical reaction can be successfully carried out.
The design and the building of a microphotoreactor operating in this UV-B domain is carried out and photochemical reactions are carried out and optimized in the microphotoreactor.
Suitable substrate families have been identified to induce a one-step or two-step mechanism of the hydrogen atom transfer (HAT). The influence of theses mechanisms on the regio and stereoselectivity of the reaction can thus be studied.
Concerning the second part of the PhD thesis, test studies on different reactions, such as cycloadditions or radical addition of our oxazolons have been carried out. First preliminary results on both reactions are encouraging.
The design and the building of a new in-house microphotoreactor operating in this UV-B domain is almost finished, which constitutes a technological novelty. Indeed, up to now, no works have been published in the literature using such LED-driven microreactor.
A systematic structural analysis of the various synthesized compounds was carried out (ICMR). Preliminary tests (pH sensitivity, solubility approach, chelating behavior), supplemented by the development of a new chromatographic method (HPLC-UV) were carried out (LGC).
The scope the photochemical reaction of the described oxazolones is large which opens additional perspectives for studies of the reaction mechanism and for application to organic synthesis.
1. Lecture at the Academia Sinica, Institute of Chemistry, Taipei, Taiwan (27/8/2019): N. Hoffmann, «Electron and Hydrogen Atom Transfer in Organic Photochemical Reactions«
2. Lecture at the National Taiwan Universtiy, Department of Chemistry, Taipei, (29/8/2019): N. Hoffmann, «Electron and Hydrogen Atom Transfer in Organic Photochemical Reactions«
3. Invited lecture at the «12th Taiwan-Japan Bilateral Symposium on Architecture on Functional Organic Molecules«, Kyoto, Japan (30/8 – 3/9/2019): N. Hoffmann, «Regio- and Stereoselectivity in Photochemical Induced Radical Reactions«
4. Oral communication at the «27th International Society of Heterocyclic Chemistry Congress«, Kyoto, Japan (1 – 6/9/2019) : N. Hoffmann, «Photochemical induced electron and hydrogen transfer in heterocyclic chemistry«
M. Latarche, N. Hoffmann, Photochemical radical cyclization reactions and cycloadditions with imine derivatives, (submitted, invited review)
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.
Monsieur Norbert Hoffmann (Institut de Chimie Moléculaire de Reims)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
ICMR Institut de Chimie Moléculaire de Reims
Hiroshima University / Department of Chemistry
LGC LABORATOIRE DE GENIE CHIMIQUE
Help of the ANR 302,770 euros
Beginning and duration of the scientific project: February 2019 - 36 Months