Synthese de 4,4'-biacridans chiraux et leur utilisation comme photocatalyseurs pour la reduction d'halogenures tertiaires (French text)

This thesis focuses on the synthesis of enantioenriched chiral photocatalysts, the 4,4′-biacridans, and their use for the photoreduction of tertiary halides. In the first part, a synthetic approach was developed to obtain the first photocatalyst, 3,3′,10,10 ′-tetramethyl-9,9′,10,10′ -tetrahydro-4,4′-biacridine. The key step of this synthesis was the preparation of a synthetic intermediate, 2,2 ′-diamino-6,6′dimethylbiphenyl and the resolution of its atropisomers by the formation of diastereomeric salts with enantiopure tartaric acid. Both enantiomers of the chiral photocatalyst were prepared from the corresponding enantiomers of this intermediate and obtained in 92 to 97% ee.; An improved version of the first photocatalyst was developed in the hope of obtaining a higher stereoselectivity in the hydrogen transfer step to the prochiral radical. The same synthetic approach was used to prepare the second photocatalyst, 1,1′,3,3′,10,10 ′-hexamethyl-9,9′,10,10′-tetrahydro-4,4 ′-biacridine in its racemic form. Once again, this practical synthesis involves, a chiral diamine, 2,2′-diamino-4,4 ′,6,6′-tetramethylbiphenyl. The resolution of this intermediate and other advanced intermediates by the formation of diastereomeric salts with different chiral acids was attempted, unfortunately without success.; Consequently, a novel synthetic approach was developed in order to isolate the enantioenriched 2,2′-diamino-4,4′,6,6 ′-tetramethylbiphenyl. This synthetic approach is based on the isolation of diastereoisomers obtained from an asymmetric Ullmann coupling using chiral oxazolines as chiral auxiliairies. The subsequent transformation of the separated diastereoisomers gave us access to the enantiomers of the second chiral photocatalyst with 80 to 92% ee.; The methodology for the photoreduction of tertiary halides using both versions of the chiral photocatalysts is also presented in this work. First, the undesirable non-catalysed reactions were minimised using α-bromo-α-methyl-γ-butyrolactone as substrate. The photocatalytic system in racemic form found to be efficient, as no undesired product was found in the reaction mixture. A better substrate, methyl 2-bromo-2-phenylpropanoate, was used in an attempt to carry out an asymmetric photocatalytic reduction. Unfortunately, no selectivity was observed. Finally, a third substrate, methyl 2-bromo-3,3-dimethyl-2-phenylbutanoate, was also reduced using the second version of the chiral photocatalyst. While efficient photoreduction was once again achieved, no selectivity was observed. In a discussion of our results, various hypotheses are put forward to explain the lack of selectivity of the hydrogen transfer step to a prochiral radical.