Synthesis and applications of planar chiral photoredox catalysts based on a [2.2]paracyclophane scaffold – PhotoChiraPhane

As a consequence of their rigid three-dimensional structure, deck-substituted [2.2]paracyclophanes (pCps) can exhibit planar chirality and are nowadays considered as promising building blocks in organic synthesis. Nevertheless, the preparation of enantiopure poly-substituted paracyclophanes is often a difficult task. The development of new processes widening the chemical space and range of applications of these chiral objects can therefore be considered as the major challenge of modern cyclophane chemistry.
The PhotoChiraPhane project will address the following objectives:
(i) Set up flexible strategies based on symmetry breaking to prepare toolbox of enantiopure compounds. Kinetic resolutions and desymmetrizations of racemic/meso derivatives will be employed to obtain poly-substituted paracyclophanes bearing on each aromatic ring of the pCp core several reactive groups suitable for regioselective orthogonal post-functionalization.
(ii) Use the enantiopure paracyclophanes as intermediates to access innovative asymmetric photoredox catalytic systems based on the paracyclophane scaffold. We will synthesize planar chiral photoactive molecules capable of enhancing the conversion of visible light into redox energy and promoting asymmetric transformations. The rigid [2.2]paracyclophane unit will serve two key functions: a) ensure close proximity of the sensitizer to the reacting partners, and b) enable the discrimination between the prochiral sites of the reaction substrate. In order to prepare the desired asymmetric catalysts, the enantiopure pCp key intermediates will therefore be decorated with different photoactive motifs and binding functional groups capable of interacting with various substrates through hydrogen bonds.
(iii) Employ the planar-chiral photoredox pCps-based catalysts to promote both known reactions and novel photoredox processes capable of generating chiral products in a stereocontrolled manner. We will focus our attention on intramolecular radical cyclizations as well as on the kinetic resolutions of racemic compound via an asymmetric cleavage of photoremovable protecting groups.
Based on the described objectives, PhotoChiraPhane is supposed to produce several interesting results, including (i) a toolbox of enantiopure pCps useful as synthetic intermediates; (ii) unprecedented photoredox catalytic systems based on planar chirality; and (iii) new asymmetric transformations activated by light. This challenging proposal is therefore expected to bring significant innovation in different areas of cyclophane chemistry (synthesis, functionalization, and modulation of the electronic properties), but also in the challenging domain of asymmetric photoredox catalysis.
PhotoChiraPhane will be conducted by two permanent researchers (the scientific coordinator, and a member of her team), together with a PhD student, who will be hired with the requested ANR grant. Three master students working for short-term training periods will also participate to the project.