Datensatz

Zusammenfassung

In this thesis, a 4-step synthesis of 3,7-bis(trifluoromethyl)-10H-phenothiazine from
commercially available phenothiazine was described. The desired product was obtained in an overall yield of 67 % over 4 steps. The Buchwald Hartwig cross-coupling of 13 with iodobenzene showed that novel N-arylphenothiazines can be accessed from
this precursor. That allows to quickly gain access to different electron-poor phenothiazines whose electrochemical and photochemical properties in the C–H functionalization of arenes can be investigated. Furthermore, the formation of PTZ salts corroborated the hypothesis of their higher absorption in the visible-light region and allowed the borylation of the anisole–PTZ salt 7. Hence, the PTZ moiety can initiate the desired C–S bond cleavage with a subsequent functionalization under visible light irradiation.
In addition, it could be proved that PTZ radical cations of 9 – which were generated by anodic oxidation – can add to anisole to form the para-functionalized PTZ salt 7 in
NMR yields up to 83 %. In contrast, the usage of the chemical oxidants copper(II) triflate and ammonium persulfate only accomplish yields of 18 % for CuOTf₂/ 0 % for NH₄S₂O₈. Hence, electrochemistry is a more efficient method to achieve the desired
PTZ salt formation. The developed electrochemical conditions for the synthesis of the PTZ salt 7 also provide an alternative for the preparation of related TT salts. For example, the anisole–TT salt 25 could be obtained in quantitative yields within 20 min.
With these results, the foundations for the usage of phenothiazines in the catalytic C–
H functionalization of arenes are set. Based on the presented data, the implementation
of the electrochemical synthesis of PTZ salts and their subsequent photochemical
functionalization together could lead to a catalytic LSF of aromatic C–H bonds in the
future. Therefore, a photo-induced functionalization reaction of PTZ salts is required that can be executed under oxidative, acidic electrochemical conditions. One option are Minisci-type reactions in which the aryl radical gets functionalized by the addition to another (hetero)arene. Since Minisci reactions have already been used for the functionalization of aryl-TFT salts and are typically robust to acids and oxidants.