Towards Oxidative Ammonium Hypoiodite Catalyzed Benzylic Functionalization of p-Cresols: Oxidative Ammoniumhypoiodit-katalysierte benzylische Funktionalisierungen von p-Kresolen

The transformation of p-cresols has been extensively investigated due to their diverse applications as starting materials in product syntheses, ranging from antioxidants and dyes to pharmaceuticals. Recent advancements in this field by a member of the research group include the ammonium salt catalyzed dearomatizative [1,5]- and benzylic [1,6]-oxidative azidation, which employs dibenzoyl peroxide as an oxidant. The site of azidation can be controlled by selecting either bromide or iodide as the counter ion of the phase transfer catalyst. This work focused at first on asymmetric azidation reactions which utilizing cinchona alkaloid derivatives as catalysts. However, by variation of the reactants, catalysts and reaction parameters, no significant improvements for both, azidation methods were achieved. Simultaneously, an electrochemical method using HFIP and H2O2 draw the attention and served as an inspiration for a second variant of phase-transfer catalyzed azidation, but its practical application in this context was not successful. However, it achieved high yields for arylation using electron-rich aromatic nucleophiles by means of Friedel-Crafts alkylation. This novel strategy was applied across a broad spectrum of p-cresols and aromatic nucleophiles and compared with an adopted method of DBPO-mediated azidation. Both strategies demonstrated high yields. The former method proved more effective in the application of less electron-rich aromatic nucleophiles, while the latter was more suitable for variously ortho-substituted p-cresols. Additionally, successful oxidative transformations to benzophenone derivatives and quinone methides were observed.